This Article Abstract Figures Only Free Full Text (Free PDF) Free Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Saved Citations Download to citation manager Request Permissions Request Reprints Add to My Marked Citations Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Citing Articles via Scopus Google Scholar Articles by Stephanopoulos, G. Articles by Lyroudia, K. Search for Related Content PubMed PubMed Citation Articles by Stephanopoulos, G. Articles by Lyroudia, K. Pubmed/NCBI databases Substance via MeSH Genetics Home Reference Genetics Home Reference - amelogenesis imperfecta Genetics Home Reference - AMELX Gene Genetics Home Reference - ENAM Gene Genetics Home Reference - MMP20 Gene Social Bookmarking                         What's this?

Genes and Related Proteins Involved in Amelogenesis Imperfecta

¹ Diploma in Dental Science, Aristotle University of Thessaloniki, Greece;
² Diploma in Biology, Aristotle University of Thessaloniki, Greece; and
³ Department of Endodontology, Dental School, Aristotle University of Thessaloniki, 23, Papafi Str., 54638 Thessaloniki, Greece

Correspondence: ^* corresponding author, lyroudia{at}zeus.csd.auth.gr

	ABSTRACT

TOP ABSTRACT INTRODUCTION AMELOGENESIS IMPERFECTA FROM GENES TO PROTEINS... CONCLUSIONS REFERENCES

 
Dental enamel formation is a remarkable example of a biomineralization process. The exact mechanisms involved in this process remain partly obscure. Some of the genes encoding specific enamel proteins have been indicated as candidate genes for amelogenesis imperfecta. Mutational analyses within studied families have supported this hypothesis. Mutations in the amelogenin gene (AMELX) cause X-linked amelogenesis imperfecta, while mutations in the enamelin gene (ENAM) cause autosomal-inherited forms of amelogenesis imperfecta. Recent reports involve kallikrein-4 (KLK4), MMP-20, and DLX3 genes in the etiologies of some cases. This paper focuses mainly on the candidate genes involved in amelogenesis imperfecta and the proteins derived from them, and reviews current knowledge on their structure, localization within the tissue, and correlation with the various types of this disorder.

Key Words: amelogenesis imperfecta • kallikrein-4 • enamelin • amelogenin • DLX3

	INTRODUCTION

TOP ABSTRACT INTRODUCTION AMELOGENESIS IMPERFECTA FROM GENES TO PROTEINS... CONCLUSIONS REFERENCES

 
Enamel, dentin, and cementum are the three major constructive components of human teeth (Schroeder, 1992). Tooth enamel is the most highly mineralized structure in the human body, with 85% of its volume occupied by unusually large, highly organized hydroxyapatite crystals (Robinson et al., 1979; Simmer and Fincham, 1995). In spite of repeated frictional forces during mastication, enamel is able to resist catastrophic wear. The physical properties and physiological function of enamel are directly related to the composition, orientation, disposition, and morphology of the mineral components within the tissue (Mahoney et al., 2003). During organogenesis, the enamel transitions from a soft and pliable tissue to its final form, almost entirely devoid of protein (Paine et al., 2001). Enamel’s final composition is a reflection of the unique molecular and cellular activities that take place. These activities are controlled by a regulated expression of multiple genes (Paine et al., 2001). Deviation from this pattern leads to amelogenesis imperfecta.

	AMELOGENESIS IMPERFECTA

TOP ABSTRACT INTRODUCTION AMELOGENESIS IMPERFECTA FROM GENES TO PROTEINS... CONCLUSIONS REFERENCES

 
The term ‘amelogenesis imperfecta’ (AI) represents a group of inherited disorders which are clinically heterogeneous and exhibit tooth enamel defects in the absence of systemic manifestations (Witkop, 1988). Both primary and permanent dentitions are affected (Aldred and Crawford, 1995). The predominant clinical manifestations of affected individuals are enamel hypoplasia (enamel is seemingly correctly mineralized but thin), hypomineralization (subdivided into hypomaturation and hypocalcification), or a combined phenotype, which is seen in most cases (Backman and Holmgren, 1988; Witkop, 1988; Aldred and Crawford, 1995). The trait of AI can be transmitted by either an autosomal-dominant, autosomal-recessive, or X-linked mode of inheritance (Backman, 1997; Aldred et al., 2003). The distribution of AI types is known to vary among different populations. In a study in Sweden, 63% of the cases were inherited as autosomal-dominant (Backman and Holmgren, 1988). In contrast, in a study in the Middle East, the most common prevalent type of AI was found to be autosomal-recessive (Chosack et al., 1979; Nusier et al., 2004).

	FROM GENES TO PROTEINS AND AMELOGENESIS IMPERFECTA

TOP ABSTRACT INTRODUCTION AMELOGENESIS IMPERFECTA FROM GENES TO PROTEINS... CONCLUSIONS REFERENCES

 
Amelogenin Gene and Protein
The amelogenin gene is a tooth-specific gene expressed in pre-ameloblasts, ameloblasts, and in the epithelial root sheath remnants (Hu et al., 2001b; Fong and Hammarström, 2000), while a low expression of amelogenin mRNAs has been recently shown in odontoblasts (Nagano et al., 2003; Papagerakis et al., 2003). Human and bovine amelogenin is expressed by genes located in the X and Y chromosomes (Nakahori et al., 1991; Gibson et al., 1992; Salido et al., 1992), while, in the mouse and rat, by a gene located only in the X chromosome (Chapman, 1991). In human males, 90% of the amelogenin transcripts are expressed from the X chromosomal copy of the gene (AMELX) (Xq22), while only 10% is expressed from the gene (AMELY) located at the Y chromosome (Yp11). Moreover, the X and Y copies are processed differently, despite being expressed in the same cells (Salido et al., 1992). The amelogenin gene is composed of 7 exons and 6 introns (Brookes et al., 1995) (Fig. 1). Exon 1 contains the 5' untranslated region of the mature mRNA. The remaining part of the 5' untranslated region is included in exon 2, where translation initiation and the signal peptide sequences are also encoded. A unique exon 4, not homologous to or evolved from the exon 4 segment expressed in humans and rodents, has been recently identified in the pig amelogenin gene (Hu CC et al., 2002). It is noteworthy that exon 6 shows considerable variation among species, due to additional internal sequence lengths (Brookes et al., 1995). Exon 7 codes for the final amino acid, Asp. It also contains the stop codon and, in humans, has been shown to contain a putative polyadenylation site (Salido et al., 1992). In addition to these known exons, Li et al.(1998) identified 2 additional exons at the 3' end of the amelogenin gene in genomic DNA of the rat. Exons 8 and 9 are 45 and 110 bp long, respectively, followed by a stop codon and a polyadenylation site. It has been confirmed that these two exons code for proteins present in the matrix of developing enamel in the rat (Baba et al., 2002). The presence of these exons in the mouse and the human genome was indicated by Southern blot analysis (Li et al., 1998). Another interesting feature is that of alternative splicing of the pre-mRNAs, resulting in multiple transcript variants that encode different isoforms (Simmer, 1995).

View larger version (49K): [in this window] [in a new window]   Figure 1. Human amelogenin gene. Mutations in amelogenesis imperfecta and phenotypic effect on enamel. The intron-exon structure of the human amelogenin gene based on the data of Salido et al.(1992). The numbered cylinders represent the exons, the line the introns. Translation of the signal sequence initiates in exon 2 (view shape in diagram), and the translation stop codon is at the beginning of exon 7 (view shape in diagram). Vertical arrows show the location of the mutations, while the branched boxes include the genomic DNA (upper row) and the mutated protein (lower row). The phenotypic effects of these proteins, as well as the references where each mutation is described, are depicted below the gene representation.

Amelogenin and X-linked Amelogenesis Imperfecta
Molecular studies and mutational analyses in patients with X-linked AI have established its correlation with the amelogenin gene. To date, the studies have identified two gene loci that are correlated with this disorder (Xp22.1-Xp22.3 and Xq24-Xq27.1) (Lau et al., 1989; Lagerström et al., 1990; Aldred et al., 1992a). Thus, genetic heterogeneity in X-linked AI may exist. To date, there are 14 AMELX-associated AI mutations (Lagerström et al., 1991; Aldred et al., 1992b; Lench et al., 1994; Lagerström-Fermer et al., 1995; Lench and Winter, 1995; Collier et al., 1997; Kindelan et al., 2000; Sekigushi et al., 2001a,b; Hart et al., 2002b; Greene et al., 2002; Kim et al., 2004). With respect to the nomenclature system devised for AMELX-associated AI mutations, exon 4 is included in the numbering scheme, although exon 4 is present in less than 1% of all transcripts (Hart et al., 2002a). The above studies showed that mutations that cause changes in domains of the protein with different functions result in diverse and distinct clinical manifestations (Wright et al., 2003). The observed phenotypes in X-linked AI vary considerably in severity, as well as in their primary features. Great variation also exists between male and female patients, because males express only one mutant allele, whereas females show a mosaic pattern of expression, due to X-chromosome inactivation (Lyonization) (Crawford and Aldred, 1992; Collier et al., 1997). With respect to the reported mutations, four are considered to include the signal peptide (Lagerström-Fermer et al., 1995; Sekigushi et al., 2001a; Kim et al., 2004) (Fig. 1). A single base substitution (g.11G>A) that resulted in a premature stop codon, two missense mutations in exon 2 that affected the translation initiation codon and/or the secretion of amelogenin (P.W4S and P.M1T), and a deletion of 9 nucleotides that replaced amino acids 5 through 8 with threonine (p.I5_A8delinsT) resulted in a clinical manifestation of hypoplasia. A combined phenotype of hypomineralization with hypomaturation, as a result of a 5-Kb deletion (g.1148_54del), including all genomic DNA from exon 3 through part of exon 7, was reported in two Swedish families (Lagerström et al., 1991). There are five described mutations concerning the C-terminal region of amelogenin (Fig. 1). All these mutations introduce a premature stop codon (Lench and Winter, 1995; Kindelan et al., 2000; Greene et al., 2002; Hart et al., 2002b). Four of these are single deletions in exon 6. The difference lies in the changes between the point of deletion and the stop codon. The loss of the C-terminal region results in a hypoplastic type of AI. The fifth mutation introduces a premature stop codon late in exon 6 (p.E191X) and a single nucleotide change (c.571G>T). There are four mutations that involve the amino-terminal region of amelogenin (Fig. 1). Three of them are single-nucleotide substitutions causing single amino-acid changes. The one that occurred in exon 5 (g.3455C>T) resulted in a phenotype described as hypomineralization/hypomaturation, while the other two, involving exon 6, resulted in a phenotype of hypomaturation with discolored enamel (Lench and Winter, 1995; Ravassipour et al., 2000; Hart et al., 2002b). The fourth was a single-nucleotide substitution that introduced a premature stop codon in exon 5 (Lench et al., 1994). Individuals appeared with a predominant combined phenotype of hypomineralization with hypomaturation, accompanied by various degrees of hypoplasia.

Enamelin Gene and Protein
The enamelin (ENAM) gene is a tooth-specific gene expressed predominantly by the enamel organ and, at a low level, in odontoblasts (Hu et al., 1998; Hu et al., 2001a; Nagano et al., 2003). ENAM cDNAs have been isolated and characterized from the mouse, the pig, and, more recently, from humans (Hu et al., 1997c, 1998; Hu CC et al., 2000). The human ENAM gene is localized on chromosome 4 (4q13.3) (Hu CC et al., 2000) and consists of only 9 exons and 8 introns (Fig. 2A) (the mouse and pig enamelin genes consist of 10 exons). Intron and exon sizes vary from 61 to 4171 bp and from 42 to 4805 bp, respectively. In humans, the sequence corresponding to mouse exon 2 is absent (Hu CC et al., 2000; Hu et al., 2001a). However, the search for the intron separating the first and second exons in the human gene showed a sequence homologous to mouse exon 2, flanked by appropriate splice junctions, raising the possibility that alternative splicing may occur (Hu et al., 2001a; Hart et al., 2003a). The translation initiation codon is assigned at the third ATG from the 5' end of the cDNA (exon 3). The first ATG is in the appropriate position for translation, but is followed in 4 codons by a stop signal (TGA). The second is not appropriate, since it contains a pyrimidine in the –3 position. The 3' untranslated region for humans is particularly long and contains 4 putative polyadenylation signals (Hu CC et al., 2000). The cDNA differs from the human gene at two positions that affect the deduced amino acid of the protein. These differences appeared to be polymorphisms. In contrast to what is observed in ameloblastin and amelogenin, no alternatively spliced enamelin mRNAs have been reported (Hu et al., 1997c; Simmer and Hu, 2002; Hart et al., 2003a).

View larger version (39K): [in this window] [in a new window]   Figure 2. Human enamelin, enamelysin, kallikrein-4, and DLX3 genes in amelogenesis imperfecta. Mutations and phenotypic effects. The exons are represented by cylinders, and introns are represented by bars. The translation initiation codon is depicted in the diagram as and the stop codon is depicted as ;. Vertical arrows show the location of the mutations, while the branched boxes include the genomic DNA (upper row) and the mutated protein (lower row). The phenotypic effects of these proteins, as well as the references where each mutation is described, are depicted below the gene representation. (A) The genomic organization of the enamelin gene is based on data from Hu CC et al.(2000) and Hu et al. (2001a). The translation start codon is in exon 3, and the translation stop codon is in exon 10. Exon 2 is shaded more darkly, as a reminder that this exon is skipped in human cDNA. (B) The genomic organization of the human enamelysin gene, based on data from Llano et al.(1997), Simmer et al.(2000), and Caterina et al.(2000). The translation start codon is in exon 1, and the translation stop codon is in exon 10. (C) The genomic organization of the human KLK4 gene, based on data by Hu JC et al.(2000). The translation start codon is in exon 2, and the translation stop codon is in exon 6. (D) DLX3 genomic organization, based on data from Price et al.(1998a).

Enamelin and Autosomal-inherited Amelogenesis Imperfecta
One autosomal-inherited form of AI, namely, autosomal-dominant amelogenesis imperfecta (ADAI), was linked to a 4Mb region on 4q21 (Kärrman et al., 1997). The ENAM gene has been mapped within this locus by radiation hybrid analysis (RHA) and fluorescent in situ hybridization (FISH), and was therefore considered a candidate gene for this type of AI (Dong et al., 2000; Hu CC et al., 2000). The reported mutational analyses of families with AI support the linkage between the ENAM gene and autosomal amelogenesis imperfecta (AAI) (Hart et al., 2003). With respect to the nomenclature system, the ENAM exhibited 10 exons and 9 introns (Hart et al., 2003a). Kida et al.(2002) first reported an autosomal-dominant hypoplastic form of AI caused by a single G-deletion within a series of 7 G residues at the exon 9-intron 9 boundary of the ENAM gene (g.8344delG). The affected individuals were heterozygous for the mutation. It was suggested that this mutation resulted in an alteration of the reading frame from exon 9 and the introduction of a premature stop codon in the 5' region of exon 10. Hart et al.(2003a) reported a G-deletion in intron 9, suggesting a potential shortening of exon 9 and the introduction of a premature stop codon. Mårdh et al.(2002) described a nonsense mutation in exon 5 (g.2382A>T). It was a single-base substitution in position 438 that resulted in a change of lysine to a stop codon, and subsequently to a truncated protein comprised only of 52 aa, compared with the wild type. The affected individuals exhibited local hypoplastic ADAI. Rajpar et al.(2001) reported a heterozygous mutation in the splice donor site of intron 8 (g.6395G>A). The most possible scenario was that the mutation caused the skipping of exon 8, resulting in an in-frame deletion of the amino acid sequence encoded by this exon. The phenotype of the affected individuals was described as thin and smooth hypoplastic ADAI. This type has been shown to map to the critical region of the ADAI local hypoplastic form, and therefore these two AI subtypes were considered allelic. Recently, Hart et al.(2003) described a 2-bp insertion mutation that resulted in a premature stop codon in exon 10 (g.13185_131186insAG). All affected individuals were homozygous for the mutation and presented with open bite and generalized hypoplastic AI. The heterozygous carriers had localized enamel-pitting defects, and none had AI or open bite. The importance of this report is that it is the first to describe the correlation between ENAM and autosomal-recessive AI (ARAI). In the same report, genetic linkage studies were consistent for localization of an ARAI locus to the AI candidate region of chromosome 4q13.3. Kim et al.(2005a) identified two ENAM mutations in kindreds with hypoplastic ADAI, one novel (g.4806A>C) and one previously identified (g.8344delG). The novel mutation alters the intron 6 splice acceptor site. Two defective splicing outcomes are probable for this mutation. The first is the inclusion of intron 6 (1615bp). This would insert multiple, in-frame stop codons preceding the most 3' exon. Translation of this transcript would add 8 novel aa to 70 aa of the wild-type protein, with the first 39 aa constituting the signal peptide. A second possible scenario would be the skipping of exon 7. This would maintain the reading frame, but would delete 87 aa (71–157) from the N-terminal side of the enamelin protein.

Ameloblastin Gene and Protein
The ameloblastin (AMBN) gene is expressed at high levels by ameloblasts (Cerny et al., 1996; Fong et al., 1996a; Lee et al., 1996) and at low levels by odontoblasts and pre-odontoblasts (Fong et al., 1998; Nagano et al., 2003), while moderate expression is also observed in Hertwig’s epithelial root sheath (Fong et al., 1996b, 1998), and in odontogenic tumors, such as in ameloblastomas (Toyosawa et al., 2000). The first reports of cloning and characterization of cDNAs encoding ameloblastin rat homologues appeared in 1996 (Krebsbach et al., 1996). Later, cDNAs from other species, such as the pig and the mouse, were also published (Hu et al., 1997b; Simmons et al., 1998). The human AMBN is localized on chromosome 4 at locus 4q21 (MacDougall et al., 1997), near other genes associated with mineralized tissues: osteopontin, bone sialoprotein, and bone morphogenetic protein 3. It consists of 13 exons and 12 introns varying in size from 39 to 1101 bp, and from 105 bp to approximately 2300 bp, respectively (Mårdh et al., 2001). The translation initiation codon is located at the 3' end of exon 1 (putative start site at 84 bp), and the translation stop codon is located in the middle of exon 13. Splice site sequences for each intron follow the 5'-gt...ag-3' rule. The human AMBN transcript is alternatively spliced, since cDNA clones of different sizes have been identified (MacDougall et al., 2000). The clones differ in a 45-bp fragment that is included or excluded. This stretch of amino acids is also alternatively spliced in the rat, mouse, and pig (Cerny et al., 1996; Hu et al., 1997b; Simmons et al., 1998). According to the human data, this fragment does not correspond to an independent exon. The 5' end of the 45-bp sequence is adjacent to intron 5, while the 3' end is within exon 6. This suggests that part of exon 6 can be excluded by the use of an alternative splice site in exon 6. The above observations differ from those of Toyosawa et al.(2000) with regard to: (a) the location of the start site, suggesting that the putative start codon is at 66 bp (exon 1); (b) the exon-intron sizes; and (c) the number of putative polyadenylation signals.

Ameloblastin, or amelin (Cerny et al., 1996), or sheathlin (Hu et al., 1997a) is present in the organic matrix and accounts for about 5% of the total protein. During investigations of pig enamel proteins, the N-terminal (Fukae and Tanabe, 1987b) and C-terminal ends (Fukae and Tanabe, 1987a; Yamakoshi et al., 2001) of ameloblastin were separately discovered due to their different biochemical properties. A comparison of the existing protein sequences for the human, pig, cattle, rat, and mouse showed high similarity (MacDougall et al., 2000), and the sequences share several features, such as the presence of potential phosphorylation sites, similar patterns of hydrophilicity, and a high proportion of Pro (15.2%), Leu (10.2%), and Gly (9%) residues. The human precursor protein is composed of 447 aa, the signal peptide is composed of 26 aa, and the mature protein of 421 aa. The fate of ameloblastin in the matrix shares similarities with that of the other proteins. Soon after secretion, the initial cleavages of the nascent ameloblastin (65 kDa) generate relatively small polypeptides containing the N-terminal and relatively large polypeptides containing the C-terminal. The N-terminal polypeptides appear to be rather stable and are gradually degraded, but not lost, during the matrix formation stage, while the C-terminal large polypeptides appear to be degraded rapidly and are soon lost from the matrix (Uchida et al., 1997; Brookes et al., 2001). Intact ameloblastin and its cleavage products containing the C-terminal are found only in the outer enamel, concentrated among the crystallites in the rod and interrod enamel (Murakami et al., 1997). Ameloblastin cleavage products containing the N-terminal side are found at all depths within the enamel layer, but they do not present a random distribution within the tissue; they concentrate in the sheath space (Uchida et al., 1995). The functional significance of this spatial distribution is not yet understood.

Enamelysin and Kallikrein-4 Genes and Proteins
The human enamelysin (MMP-20) gene, located in chromosome 11 (11q22.3-q23) (Llano et al., 1997), is comprised of 10 exons and 9 introns (Caterina et al., 2000), with sizes varying from 104 to 310 bp and 806 to 14,296 bp, respectively. The start codon (ATG) is located in exon 1, while the stop codon is located in exon 10 (Fig. 2B). To date, MMP-20 is considered a tooth-specific gene, since Northern blot analysis of RNAs that were obtained from multiple human tissues failed to show any positive hybridization signal with human enamelysin probes (Llano et al., 1997). Additionally, no other intact, physiologically normal, tissue has been demonstrated to express MMP-20, apart from ameloblasts, pre-ameloblasts, and odontoblasts (Bartlett, 2004), whereas the expression of MMP-20 in human odontogenic tumors and carcinoma cell lines originating from the tongue has recently been described (Bègue-Kirn et al., 1998; Caterina et al., 2000; Takata et al., 2000; Väänänen et al., 2001). The cloning and characterization of cDNAs from different species, including humans, pigs, mice, and cattle, has been reported (Llano et al., 1997; Bartlett et al., 1998; Den Besten et al., 1998; Caterina et al., 2000).

MMP-20 gene codes for a calcium-dependent (Bartlett et al., 1998) proteinase that is a member of the matrix metallopeptidases family (MMPs) (Rawlings et al., 2004). This protein family is characterized by a common domain structure, which also applies in the case of MMP-20. MMP-20 is divided into the following domains: signal peptide (1–22), propeptide (23–107), catalytic domain (108–271), linker (272–295), and hemopexin (296–483). The pre-proprotein has 483 aa, the proprotein has 461 aa, while the active protein has 376 aa (Simmer and Hu, 2002). However, MMP-20 possesses several unique structural features that define it as a novel MMP. First, the MMP-20 amino acid sequence contains no N-linked glycosylation sites (Bartlett et al., 1996). Second, it lacks two of the three residues important in defining the active site of a collagenase, and lacks all three of the residues important in defining the active site of a stromelysin (Bartlett et al., 1996; Llano et al., 1997). Third, MMP-20, in contrast to stromelysins and collagenases, has a unique hinge region of 24 residues that connects the catalytic domain to the hemopexin-like domain (Bartlett et al., 1996; Llano et al., 1997; Caterina et al., 2000). An amino acid sequence comparison between human MMP-20 (Llano et al., 1997) and that reported for porcine MMP-20 revealed a high percentage of identity (89%). The active protease migrates as a doublet at 46 kDa and 41 kDa on zymograms (Yamada et al., 2003). MMP-20 is the early protease, and it is expressed throughout the secretory stage and part of the maturation stage (Bartlett et al., 1996; Bègue-Kirn et al., 1998; Bartlett and Simmer, 1999). Immunohistochemical studies have showed the presence of enamelysin within the secretory enamel, with the greatest staining occurring adjacent to the secretory face of Tomes’ process (Fukae et al., 1998).

Kallikrein-4 (KLK4), or prostase, or EMPS1, or KLK-L1, or PRSS17 (serine proteinase 17) was first extracted in 1977 from developing porcine enamel (Fukae et al., 1977), and the first cDNA and protein sequence was deduced from a cDNA library (Simmer et al., 1998). Different groups have isolated the human cDNA from a variety of tissues, such as the central nervous system and the prostate (Nelson et al., 1999; Stephenson et al., 1999), and, more recently, from developing human tooth tissues (Simmer et al., 2000). The KLK4 gene is located near the telomere of chromosome 19 (19q13.3–19q13.4) downstream of the KLK2 gene, and is considered a member of the human tissue kallikrein gene family (Du Pont et al., 1999; Diamantis et al., 2000; Hu JC et al., 2000). A further characterization of the KLK4 gene, extending its 3' downstream sequence and identifying potentially important polymorphisms, has been reported (Hu JC et al., 2000). These investigators also identified an additional exon. The human DNA sequence is of 7115 bp and consists of 6 exons (5 of which are coding) and 5 introns. The exons vary in sizes from 72 to 251 bp, and intron sizes vary from 83 to 1357 bp. The translation initiation codon (ATG) is located in exon 2 (first coding exon) (660–662 bp), and the termination codon (TGA) is located in exon 6 (fifth coding exon) (5108–5110) (Fig. 2C). The sequences encoding the amino acids of the catalytic triad presented in the enzyme are located at coding exons 2, 3, and 5, respectively. KLK4 is expressed by both ameloblasts and odontoblasts (Hu JC et al., 2000; Nagano et al., 2003). A splice variant lacking exon 6 has been described in skin and endometrial tumor cultures (Myers and Clements, 2001; Komatsu et al., 2003), but its role has not yet been defined.

KLK4 protein is a calcium-independent serine protease. KLK4 is secreted as an inactive zymogen of 230 aa that becomes the active protein (224 aa) with the removal of a 6 aa propeptide by MMP-20 (Ryu et al., 2002). Human KLK4 has six disulfide bridges and one potential N-linked glycosylation site away from the active site of the enzyme. Of great importance for KLK4’s function is a triad of catalytic amino acids (H71, S207, and D116) (Komatsu et al., 2003). Despite its most recent official designation, KLK4 is no more closely related to the original kallikreins than it is to the trypsins. The kallikrein loop, a structural feature common to the kallikrein proteases, is absent in KLK4. A single amino acid insertion that is common to the pig, mouse, and human gene is absent from the kallikreins (Hu JC et al., 2000; Ryu et al., 2002). KLK4 is the late protease; its expression by ameloblasts begins in the transition stage and continues throughout enamel maturation (Hu JC et al., 2000, 2002). The KLK4 activity observed in the highly mineralized enamel at the dentino-enamel junction during the secretory stage is due to the gene’s expression from the odontoblasts (Fukae et al., 2002). KLK4 is responsible for the degradation of the TRAP amelogenin cleavage product to smaller fragments.

DLX3 Gene and Protein
The DLX3 gene is a member of the family of homeobox genes that are homologous to the distalless (Dll) gene of Drosophila, known to be expressed during development of the chondrocranium, dermatocranium, sensory organs, brain, limbs, and appendages, and in the processes of osteogenesis and hematopoiesis (Robinson and Mahon, 1994; Weiss et al., 1998). The mammalian genes take the form of bigene clusters, namely, Dlx2-1, Dlx5-6, and Dlx3-7. Scherer et al.(1995) mapped the human homologue of the mouse Dlx3 gene to 17q21.3-q22, which consists of 3 exons, with the homeodomain contained in exons 2 and 3. Exons 1 and 2 are separated by a 1.1-kb intron; exons 2 and 3 are separated by a 1.6-kb intron (Fig. 2D). The start codon is located in exon 1, while the stop codon is in exon 3 (Price et al., 1998a). The encoded DLX3 human protein (GenBank accession number NP_005211) is a 31738-Da protein composed of 287 aa with a 60 aa homeodomain (129–188 aa). As with all DLX proteins, it shares similar DNA-binding sites and is thought to act as a homeodomain transcription factor, having N-terminal and C-terminal regions that act as transcriptional activators (Bryan and Morasso, 2000). Therefore, the presence of these proteins is considered critical for craniofacial, tooth, brain, hair, and neural development.

Ameloblastin, Enamelysin, Kallikrein-4, and DLX3 in Amelogenesis Imperfecta
AMBN gene loci are on chromosome 5 in the mouse (Krebsbach et al., 1996) and chromosome 4q21 in humans (MacDougall et al., 1997). AMBN maps within the critical region for autosomal-dominant AI, and therefore is considered as a candidate gene. However, it was excluded from a causative role by mutational analyses within the families studied by Mårdh et al.(2001). As far as KLK4 is concerned, Hart et al.(2004) identified the mutation (g.2142G>A) (Fig. 2C) that resulted in a truncated protein containing 152 aa and lacking the S207 site, which, as we previously mentioned, is essential for the function of the enzyme. Due to the abnormal enzymic activity, the crystallites of the enamel grew to the normal length but incompletely in thickness (Hart et al., 2004). This is the first report of mutation in this gene found to cause ADAI. Kim et al.(2005b) identified a homozygous mutation in the MMP-20 gene in two affected members of a family with autosomal-recessive pigmented hypomaturation AI. The mutation destroyed the splice acceptor at the 3' end of intron 6 (AGTG) and resulted in a hypomatured enamel product. Two defective splicing outcomes seem to be most probable, both of which would introduce an upstream translation termination codon in the mRNA transcript. In the first scenario, the retention of intron 6 in the mRNA would generate a large mRNA with translation terminating in the first complete codon of the retained intron (p.I1319X). In the second splicing scenario, exon 7 would not be recognized as an exon and would be skipped. Skipping exon 7 would shift the reading frame after R318 and would introduce 19 extraneous aa before terminating translation (p.I1319fs338X) (Kim et al., 2005b) (Fig. 2B). A comparison of the dental phenotypes of the KLK4 and MMP-20 probands shows that they share many similar features (Kim et al., 2005b).

Dong et al.(2005) demonstrated that a mutation within the human DLX3 gene homeodomain is associated with amelogenesis imperfecta (hypoplastic-hypomaturation type), with taurodontism (AIHHT). This 2-bp deletion (CT) in exon 3 (Fig. 2D) causes a frameshift within the last two amino acids of the homeodomain, with a premature stop codon truncating the protein by 88 aa. This is the first report of a mutation within the homeodomain of DLX3. Previous studies have shown a DLX3 mutation, outside the homeodomain, associated with trichodento-osseous syndrome (TDO) (Price et al., 1998a,b). Dong et al.(2005) suggested that TDO and some forms of AIHHT are allelic. However, this requires further investigation.

However, AMELX, AMBN, ENAM, KLK4, and MMP-20 were excluded from a causative role in two families with autosomal-dominant hypocalcified AI, suggesting that this type of AI is caused by mutation of a gene that is either not known or not considered to be a major contributor to enamel formation (Hart et al., 2003b).

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION AMELOGENESIS IMPERFECTA FROM GENES TO PROTEINS... CONCLUSIONS REFERENCES

 
Amelogenesis imperfecta (AI) is a group of inherited defects of dental enamel formation that shows both clinical and genetic heterogeneity. Great progress has been made regarding the definition of the genetic background in AI. To date, mutations in 5 genes (AMELX, ENAM, KLK4, MMP-20, and DLX3) have been found to cause AI. Alterations in the AMELX gene are responsible for X-linked AI. The various enamel phenotypes observed in families with X-linked AI correlate with the sites of mutation within the coding region of the amelogenin gene. Mutations in the ENAM, KLK4, and MMP-20 genes cause AI with the autosomal pattern of inheritance. Recently, a mutation within the DLX3 gene has been described and associated with AIHHT. AMBN is another candidate gene for autosomal-dominant amelogenesis imperfecta, but the involvement of this gene in the disease has not yet been established. However, genes that have so far been proposed as candidates for AI do not cause some forms of autosomal-dominant hypocalcified AI. It is expected that future research will help establish genotype-phenotype correlations for all autosomal forms of AI. As the knowledge regarding genetic mutations associated with the various types of AI increases, our ability to make an accurate diagnosis of AI will be remarkably improved. The similarity in the clinical features of the different AI types makes the differentiation among them difficult at the clinical level. Correlation of the genetic mutations with the clinical phenotypes will be extremely valuable for managing patients with AI. Moreover, this knowledge allows us to make better predictions of the AI types that are associated with problems such as calculus formation and skeletal open bites, and to select the most optimal treatment approaches for each case.

Received for publication January 25, 2005. Accepted for publication May 19, 2005.

	REFERENCES

TOP ABSTRACT INTRODUCTION AMELOGENESIS IMPERFECTA FROM GENES TO PROTEINS... CONCLUSIONS REFERENCES

 

• Aldred MJ, Crawford PJ (1995). Amelogenesis imperfecta—towards a new classification. Oral Dis 1:2–5.[Medline] [Order article via Infotrieve]
• Aldred MJ, Crawford PJ, Roberts E, Gillespie CM, Thomas NS, Fenton I, et al. (1992a). Genetic heterogeneity in X-linked amelogenesis imperfecta. Genomics 14:567–573.[CrossRef][Medline] [Order article via Infotrieve]
• Aldred MJ, Crawford PJ, Roberts E, Thomas NS (1992b). Identification of a nonsense mutation in the amelogenin (AMELX) gene in a family with X-linked amelogenesis imperfecta (AIH1). Hum Genet 90:413–416.[Medline] [Order article via Infotrieve]
• Aldred MJ, Savarirayan R, Crawford PJ (2003). Amelogenesis imperfecta: a classification and catalogue for the 21st century (review). Oral Dis 9:19–23.[CrossRef][Medline] [Order article via Infotrieve]
• Baba O, Takahashi N, Terashima T, Li W, DenBesten PK, Takano Y (2002). Expression of alternatively spliced RNA transcripts of amelogenin gene exons 8 and 9 and its end products in the rat incisor. J Histochem Cytochem 50:1229–1236.[Abstract/Free Full Text]
• Backman B (1997). Inherited enamel defects (review). Ciba Found Symp 205:175–182; discussion 183–186.[Medline] [Order article via Infotrieve]
• Backman B, Holmgren G (1988). Amelogenesis imperfecta: a genetic study. Hum Hered 38:189–206.[Medline] [Order article via Infotrieve]
• Bartlett JD (2004). Enamelysin. In: Handbook of proteolytic enzymes. Barrett A, Rawlings N, Woessner J, editors. San Diego, CA: Academic Press, pp. 561–564.
• Bartlett JD, Simmer JP (1999). Proteinases in developing dental enamel. Crit Rev Oral Biol Med 10:425–441.[Abstract/Free Full Text]
• Bartlett JD, Simmer JP, Margolis HC, Moreno EC (1996). Molecular cloning and mRNA tissue distribution of a novel matrix metallo-proteinase isolated from porcine enamel organ. Gene 183:123–128.[CrossRef][Medline] [Order article via Infotrieve]
• Bartlett JD, Ryu OH, Xue J, Simmer JP, Margolis, HC (1998). Enamelysin mRNA displays a developmentally defined pattern of expression and encodes a protein which degrades amelogenin. Connect Tissue Res 39:101–109; discussion 141–149.[Medline] [Order article via Infotrieve]
• Bègue-Kirn C, Krebsbach PH, Bartlett JD, Butler WT (1998). Dentin sialoprotein, dentin phosphoprotein, enamelysin and ameloblastin: tooth-specific molecules that are distinctively expressed during murine dental differentiations. Eur J Oral Sci 106:963–970.[CrossRef][Medline] [Order article via Infotrieve]
• Brookes SJ, Robinson C, Kirkham J, Bonass WA (1995). Biochemistry and molecular biology of amelogenin proteins of developing dental enamel (review). Arch Oral Biol 40:1–14.[CrossRef][Medline] [Order article via Infotrieve]
• Brookes SJ, Kirkham J, Shore RC, Wood SR, Slaby I, Robinson C (2001). Amelin extracellular processing and aggregation during rat incisor amelogenesis. Arch Oral Biol 46:201–208.[CrossRef][Medline] [Order article via Infotrieve]
• Bryan J, Morasso M (2000). The Dlx3 protein harbors basic residues required for nuclear localization, transcriptional activity and binding to Msx1. J Cell Sci 113:4013–4023.[Abstract]
• Catalano-Sherman J, Palmon A, Burstein Y, Deutsch D (1993). Amino acid sequence of a major human amelogenin protein employing Edman degradation and cDNA sequencing. J Dent Res 72:1566–1572.
• Caterina J, Shi J, Sun X, Qian Q, Yamada S, Liu Y, et al. (2000). Cloning, characterization, and expression analysis of mouse enamelysin. J Dent Res 79:1697–1703.
• Cerny R, Hammarström L (1998). Cloning cDNA sequence and alternative splicing of guinea-pig amelogenin mRNAs (abstract). In: Proceedings, Sixth International Conference on the Chemistry and Biology of Mineralized Tissues. Robinson C, Goldberg M, editors. Vittel, France: Abstract No. 38.
• Cerny R, Hammarström L (1999). NCBI protein database. Accession No. AJ012200.
• Cerny R, Hammarström L, Wurtz T (1996). A novel gene expressed in rat codes for proteins with cell-binding domains. J Bone Miner Res 11:883–891.[Medline] [Order article via Infotrieve]
• Chapman VM (1991). Linkage of amelogenin (Amel) to the distal portion of the mouse X chromosome. Genomics 10:23–28.[CrossRef][Medline] [Order article via Infotrieve]
• Chosack A, Eindelman E, Wisotski I, Cohen T (1979). Amelogenesis imperfecta among Israeli Jews and the description of a new type of local hypoplastic autosomal recessive amelogenesis imperfecta. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 47:148–156.
• Collier PM, Sauk JJ, Rosenbloom J, Yuan ZA, Gibson CW (1997). An amelogenin gene defect associated with human X-linked amelogenesis imperfecta. Arch Oral Biol 42:235–242.[CrossRef][Medline] [Order article via Infotrieve]
• Crawford PJ, Aldred MJ (1992). X-linked amelogenesis imperfecta. Presentation of two kindreds and a review of the literature. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 73:449–455.
• Delgado S, Girondot M, Sire JY (2005). Molecular evolution of amelogenin in mammals. J Mol Evol 60:12–30.[CrossRef][Medline] [Order article via Infotrieve]
• Den Besten PK, Punzi J, Li W (1998). Purification and sequencing of a 21-kDa and 25-kDa bovine enamel metalloproteinase. Eur J Oral Sci 106(Suppl 1):345–349.
• Diamantis EP, Yousef OM, Clements J, Ashworth LK, Lilja H, Stenman UH, et al. (2000). New nomenclature for the human tissue kallikrein gene family. Clin Chem 46:1855–1858.[Free Full Text]
• Dong J, Gu TT, Simmons D, MacDougall M (2000). Enamelin maps to human chromosome 4q21 within the autosomal dominant amelogenesis imperfecta locus. Eur J Oral Sci 108:353–358.[CrossRef][Medline] [Order article via Infotrieve]
• Dong J, Amor D, Aldred MJ, Gu TT, Escamilla M, MacDougall M (2005). DLX3 mutation associated with autosomal dominant amelogenesis imperfecta with taurodontism. Am J Med Genet A 133:138–141.
• Du Pont BR, Hu CC, Reveles X, Simmer JP (1999). Assignment of serine protease 17 (PRSS17) to human chromosome band(s) 19q13.3–q13.4 by in situ hybridization. Cytogenet Cell Genet 86:212–213.[Medline] [Order article via Infotrieve]
• Fincham AG, Moradian-Oldak J (1993). Amelogenin post-translational modifications: carboxy-terminal processing and the phosphorylation of bovine and porcine "TRAP" and "LRAP" amelogenins. Biochem Biophys Res Commun 197:248–255.[CrossRef][Medline] [Order article via Infotrieve]
• Fincham AG, Belcourt AB, Termine JD, Butler WT, Cothran WC (1981). Dental enamel matrix: sequences of two amelogenin polypeptides. Biosci Rep 1:771–778.[CrossRef][Medline] [Order article via Infotrieve]
• Fincham AG, Moradian-Oldak J, Sarte PE (1994). Mass-spectrographic analysis of porcine amelogenin identifies a single phosphorylated locus. Calcif Tissue Int 55:398–400.[CrossRef][Medline] [Order article via Infotrieve]
• Fong CD, Hammarström L (2000). Expression of amelin and amelogenin in epithelial root sheath remnants of fully formed rat molars. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 90:218–223.[CrossRef][Medline] [Order article via Infotrieve]
• Fong CD, Hammarström L, Lundmark C, Wurtz T, Slaby I (1996a). Expression patterns of RNAs from amelin and amelogenin in developing rat molars and incisors. Adv Dent Res 10:195–200.[Abstract/Free Full Text]
• Fong CD, Slaby I, Hammarström C (1996b). Amelin: an enamel-related protein, transcribed in the cells of epithelial root sheath. J Bone Miner Res 11:883–891.[Medline] [Order article via Infotrieve]
• Fong CD, Cerny R, Hammarström L, Slaby I (1998). Sequential expression of an amelin gene in mesenchymal and epithelial cells during odontogenesis in rats. Eur J Oral Sci 106(Suppl 1):324–330.
• Fukae M, Tanabe T (1987a). ⁴⁵Ca-labeled proteins found in porcine developing dental enamel at an early stage of develompment. Adv Dent Res 1:261–266.[Abstract/Free Full Text]
• Fukae M, Tanabe T (1987b). Nonamelogenin components of porcine enamel in the protein fraction free from the enamel crystals. Calcif Tissue Int 40:286–293.[Medline] [Order article via Infotrieve]
• Fukae M, Tanabe T, Shimizu M (1977). Proteolytic enzyme activity in porcine immature enamel. Tsurumi U Dent J 3:15–17.
• Fukae M, Tanabe T, Uchida T, Yamakoshi Y, Shimizu M (1993). Enamelins in the newly formed bovine enamel. Calcif Tissue Int 53:257–261.[CrossRef][Medline] [Order article via Infotrieve]
• Fukae M, Tanabe T, Murakami C, Dohi N, Uchida T, Shimizu M (1996). Primary structure of porcine 89-kDa enamelin. Adv Dent Res 10:111–118.[Abstract/Free Full Text]
• Fukae M, Tanabe T, Uchida T, Lee SK, Ryu OH, Murakami C, et al. (1998). Enamelysin (matrix metalloproteinase-20): localization in the developing tooth and effects of pH and calcium on amelogenin hydrolysis. J Dent Res 77:1580–1588.
• Fukae M, Tanabe T, Nagano T, Ando H, Yamakoshi Y, Yamada M, et al. (2002). Odontoblasts enhance the maturation of enamel crystals by secreting EMPS1 at the enamel-dentin junction. J Dent Res 81:668–672.
• Gibson CW, Golub EE, Abrams WR, Shen G, Ding W, Rosenbloom J (1992). Bovine amelogenin message heterogeneity: alternative splicing and Y-chromosomal gene transcription. Biochemistry 31:8384–8388.
• Greene SR, Yuan ZA, Wright JT, Amjad AH, Abrams WR, Buchanan JA, et al. (2002). A new frameshift mutation encoding a truncated amelogenin leads to X-linked amelogenesis imperfecta. Arch Oral Biol 47:211–217.[CrossRef][Medline] [Order article via Infotrieve]
• Hart PS, Hart TC, Simmer JP, Wright JT (2002a). A nomenclature for X-linked amelogenesis imperfecta (review). Arch Oral Biol 47:225–260.
• Hart PS, Aldred MJ, Crawford PJM, Wright NJ, Hart TC, Wright JT (2002b). Amelogenesis imperfecta phenotype-genotype correlations with two amelogenin gene mutations. Arch Oral Biol 47:261–265.[CrossRef][Medline] [Order article via Infotrieve]
• Hart PS, Michalec MD, Seow WK, Hart TC, Wright JT (2003a). Identification of the enamelin (g.8344delG) mutation in a new kindred and presentation of a standardized ENAM nomenclature. Arch Oral Biol 48:589–596.[CrossRef][Medline] [Order article via Infotrieve]
• Hart PS, Wright JT, Savage M, Kang G, Bensen JT, Gorry MC, et al. (2003b). Exclusion of candidate genes in two families with autosomal dominant hypocalcified amelogenesis imperfecta. Eur J Oral Sci 111:326–331.[CrossRef][Medline] [Order article via Infotrieve]
• Hart PS, Hart TC, Michalec MD, Ryu OH, Simmons D, Hong S, et al. (2004). Mutation in kallikrein 4 causes autosomal recessive hypomaturation amelogenesis imperfecta. J Med Genet 41:545–549.[Free Full Text]
• Hart TC, Hart PC, Gorry MC, Michalec MD, Ryu OH, Uygur C, et al. (2003). Novel ENAM mutation responsible for autosomal recessive amelogenesis imperfecta and localised enamel defects. J Med Genet 40:900–906.[Abstract/Free Full Text]
• Hu CC, Ryu OH, Qian Q, Zhang CH, Simmer JP (1997a). Cloning characterization and heterologous expression of exon-4-containing amelogenin mRNAs. J Dent Res 76:641–647.
• Hu CC, Fukae M, Uchida T, Qian Q, Zhang CH, Ryu OH, et al. (1997b). Sheathlin: cloning cDNA/polypeptide sequences and immunolocalization of porcine enamel sheath proteins. J Dent Res 76:648–657.
• Hu CC, Ryu OH, Qiang Q, Zhang CH, Simmer JP (1997c). Cloning and characterization of porcine enamelin mRNAs. J Dent Res 76:1720–1729.
• Hu CC, Simmer JP, Bartlett JD, Qian Q, Ryu OH, Xue J, et al. (1998). Murine enamelin: cDNA and derived protein sequences. Connect Tissue Res 39:47–61; discussion 63–67.[Medline] [Order article via Infotrieve]
• Hu CC, Hart TC, Dupont BR, Chen JJ, Sun X, Qian Q, et al. (2000). Cloning human enamelin cDNA chromosomal localization and analysis of expression during tooth formation. J Dent Res 79:912–919.
• Hu CC, Ryu OH, Yamakoshi Y, Zhang CH, Cao X, Qiang Q, et al. (2002). Pig amelogenin expresses a unique exon 4. Connect Tissue Res 43:435–440.[CrossRef][Medline] [Order article via Infotrieve]
• Hu JC, Zhang C, Sun X, Yang Y, Cao X, Ryu OH, et al. (2000). Characterization of the mouse and human PRSS17 genes, their relationship to other serine proteases and the expression of PRSS17 in developing mouse incisors. Gene 251:1–8.[CrossRef][Medline] [Order article via Infotrieve]
• Hu JC, Zhang C, Yang Y, Mårdh KC, Forsman-Semb K, Simmer JP (2001a). Cloning and characterization of the mouse and human enamelin genes. J Dent Res 80:898–902.
• Hu JC, Sun X, Zhang C, Simmer JP (2001b). A comparison of enamelin and amelogenin expression in developing mouse molars. Eur J Oral Sci 109:125–132.[CrossRef][Medline] [Order article via Infotrieve]
• Hu JC, Sun X, Zhang CH, Liu S, Bartlett JD, Simmer JP (2002). Enamelysin and kallikrein-4 expression in developing mouse molars. Eur J Oral Sci 110:307–315.[CrossRef][Medline] [Order article via Infotrieve]
• Kärrman C, Backman B, Dixon M, Holmgren G, Forsman K (1997). Mapping of the locus for autosomal dominant amelogenesis imperfecta (AIH2) to a 4Mb Yac Contig on chromosome 4q11–q21. Genomics 39:164–170.[CrossRef][Medline] [Order article via Infotrieve]
• Kida M, Ariga T, Shirakawa T, Oguchi H, Sakiyama Y (2002). Autosomal-dominant hypoplastic form of amelogenesis imperfecta caused by an enamelin gene mutation at the exon-intron boundary. J Dent Res 81:738–742.
• Kim J-W, Simmer JP, Hu YY, Lin BP-L, Boyd C, Wright JT, et al. (2004). Amelogenin p.M1T and p.W4S mutations underlying hypoplastic X-linked amelogenesis imperfecta. J Dent Res 83:378–383.
• Kim J-W, Seymen F, Lin BP, Kiziltan B, Gencay K, Simmer JP, et al. (2005a). ENAM mutations in autosomal-dominant amelogenesis imperfecta. J Dent Res 84:278–282.
• Kim J-W, Simmer JP, Hart TC, Hart PS, Ramaswami MD, Bartlett JD, et al. (2005b). MMP-20 mutation in autosomal recessive pigmented hypomaturation amelogenesis imperfecta. J Med Genet 42:271–275.[Free Full Text]
• Kindelan S, Brook A, Gangemi L, Lench N, Wong F, Fearne J, et al. (2000). Detection of a novel mutation in X-linked amelogenesis imperfecta. J Dent Res 79:1978–1982.
• Komatsu N, Takata M, Otsuki N, Toyama T, Ohka R, Takehara K, et al. (2003). Expression and localization of tissue kallikrein mRNAs in human epidermis and appendages. J Invest Dermatol 121:542–549.[CrossRef][Medline] [Order article via Infotrieve]
• Krebsbach PH, Lee SK, Matsuki Y, Kozak CA, Yamada KM, Yamada Y (1996). Full-length sequence, localization and chromosomal mapping of ameloblastin: a novel tooth specific gene. J Biol Chem 271:4431–4435.[Abstract/Free Full Text]
• Lagerström M, Dahl N, Iselius L, Backman B, Pettersson U (1990). Mapping of the gene for X-linked amelogenesis imperfecta by linkage analysis. Am J Hum Genet 46:120–125.[Medline] [Order article via Infotrieve]
• Lagerström M, Dahl N, Nakahori Y, Nakagome Y, Backman B, Landegren U, et al. (1991). A deletion in the amelogenin gene (AMG) causes X-linked amelogenesis imperfecta (AIH1). Genomics 10:971–975.[CrossRef][Medline] [Order article via Infotrieve]
• Lagerström-Fermer M, Nilsson M, Backman B, Salido EC, Shapiro C, Pettersson U, et al. (1995). Amelogenin signal peptide mutation: correlation between mutations in the amelogenin gene (AMGX) and manifestations of X-linked amelogenesis imperfecta. Genomics 26:159–162.[CrossRef][Medline] [Order article via Infotrieve]
• Lau EC, Mohandas T, Shapiro LJ, Slavkin HC, Snead ML (1989). Human and mouse amelogenin gene loci are on the sex chromosomes. Genomics 4:162–168.[CrossRef][Medline] [Order article via Infotrieve]
• Lee SK, Krebsbach PH, Matsuki Y, Nansi A, Yamada KM, Yamada Y (1996). Ameloblastin expression in rat incisors and human tooth germs. Int J Dev Biol 40:1141–1150.[Medline] [Order article via Infotrieve]
• Lench NJ, Winter GB (1995). Characterization of molecular defects in X-linked amelogenesis imperfecta (AIH1). Hum Mutat 5:251–259.[CrossRef][Medline] [Order article via Infotrieve]
• Lench NJ, Brook AH, Winter GB (1994). SSCP detection of a nonsense mutation in exon 5 of the amelogenin gene (AMGX) causing X-linked amelogenesis imperfecta. Hum Mol Genet 3:827–828.[Free Full Text]
• Li W, Mathews C, Gao C, Den Besten PK (1998). Identification of two additional exons at the 3' end of the amelogenin gene. Arch Oral Biol 43:497–504.[CrossRef][Medline] [Order article via Infotrieve]
• Llano E, Pendás AM, Knäuper V, Sorsa T, Salo T, Salido EC, et al. (1997). Identification and structural and functional characterization of human enamelysin gene (MMP-20). Biochemistry 36:15101–15108.[Medline] [Order article via Infotrieve]
• Lyaruu DM, Hu CC, Zhang C, Qian Q, Ryu OH, Moradian-Oldak J, et al. (1998). Derived protein and cDNA sequences of hamster amelogenin. Eur J Oral Sci 106(Suppl 1):299–307.
• MacDougall M, Dupont BR, Simmons D, Reus B, Krebsbach PH, Kärrman C, et al. (1997). Ameloblastin gene (AMBN) maps within the critical region for autosomal dominant amelogenesis imperfecta at chromosome 4q21. Genomics 41:115–118.[CrossRef][Medline] [Order article via Infotrieve]
• MacDougall M, Simmons D, Gu TT, Forsman-Semb K, Kärrman C, Mesbah M, et al. (2000). Cloning characterization and immunolocalization of human ameloblastin. Eur J Oral Sci 108:303–310.[Medline] [Order article via Infotrieve]
• Mahoney EK, Rohanizadeh R, Smail FSM, Kilpatrick NM, Swain MV (2003). Mechanical properties and microstructure of hypomineralized enamel of permanent teeth. Biomaterials 25:5091–5100.
• Mårdh-Kärrman C, Backman B, Simmons D, Golovleva I, Gu TT, Holmgren G, et al. (2001). Human ameloblastin gene: genomic organization and mutation analysis in amelogenesis imperfecta patients. Eur J Oral Sci 109:8–13.[CrossRef][Medline] [Order article via Infotrieve]
• Mårdh KC, Backman B, Holmgren G, Hu J-CC, Simmer JP, Forsman-Semb K (2002). A nonsense mutation in the enamelin gene causes local hypoplastic autosomal dominant amelogenesis imperfecta (AIH2). Hum Mol Genet 11:1069–1074.[Abstract/Free Full Text]
• Murakami C, Dohi N, Fukae M, Tanabe T, Yamakoshi Y, Wakida K, et al. (1997). Immunochemical and immunohistochemical study of the 27-and 29-kDa calcium binding proteins and related proteins in the porcine tooth germ. Histochem Cell Biol 107:485–494.
• Myers SA, Clements JA (2001). Kallikrein-4, a new member of the human kallikrein gene family is up regulated by estrogen and progesterone in the human endometrial cancer cell line, KLE. J Clin Endocrinol Metab 86:2323–2326.[Abstract]
• Nagano T, Oida S, Ando H, Gomi K, Arai T, Fukae M (2003). Relative levels of mRNA encoding enamel proteins in enamel organ epithelia and odontoblasts. J Dent Res 82:982–986.
• Nakahori Y, Takenaka O, Nakagome Y (1991). A human X-Y homologous region encodes "amelogenin". Genomics 9:264–269.[CrossRef][Medline] [Order article via Infotrieve]
• Nelson PS, Gan L, Ferguson C, Moss P, Gelinas R, Hood L, Wang K (1999). Molecular cloning and characterization of prostase, an androgen-regulated serine protease with prostate-restricted expression. Proc Natl Acad Sci USA 96:3114–3119.[Abstract/Free Full Text]
• Nusier M, Yassin O, Hart TC, Samini A, Wright JT (2004). Phenotypic diversity and revision of the nomenclature for autosomal recessive amelogenesis imperfecta. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 97:220–230.[Medline] [Order article via Infotrieve]
• Paine ML, White SN, Luo W, Fong H, Sarikaya M, Snead ML (2001). Regulated expression dictates enamel structure and tooth function (review). Matrix Biol 20:273–292.[CrossRef][Medline] [Order article via Infotrieve]
• Papagerakis P, MacDougall M, Hotton D, Bailleu-Forestier I, Oboeuf M, Berdal A (2003). Expression of amelogenin in odontoblasts. Bone 32:228–240.
• Price JA, Bowden DW, Wright JT, Pettenati MJ, Hart TC (1998a). Identification of a mutation in DLX3 associated with tricho-dento-osseous (TDO) syndrome. Hum Mol Genet 7:563–569.[Abstract/Free Full Text]
• Price JA, Wright JT, Kula K, Bowden DW, Hart TC (1998b). A common DLX3 gene mutation is responsible for tricho-dento-osseous syndrome in Virginia and North Carolina families. J Med Genet 35:825–828.[Abstract/Free Full Text]
• Rajpar MH, Harley K, Laing C, Davies DM, Dixon MJ (2001). Mutation of the gene encoding the enamel-specific protein, enamelin, causes autosomal-dominant amelogenesis imperfecta. Hum Mol Genet 10:1673–1677.[Abstract/Free Full Text]
• Ravassipour DB, Hart S, Hart TC, Ritter AV, Yamauchi RM, Gibson CW, et al. (2000). Unique enamel phenotype associated with amelogenin gene (AMELX) codon 41 point mutation. J Dent Res 79:1476–1481.
• Rawlings ND, Tolle DP, Barrett AJ (2004). MEROPS: the peptidase database. Nucleic Acids Res 32(Database issue):D160–D164.[Abstract/Free Full Text]
• Robinson C, Briggs HD, Atkinson PJ, Weatherell JA (1979). Matrix and mineral changes in developing enamel. J Dent Res 58(Spec Iss B):871–882.
• Robinson GW, Mahon KA (1994). Differential and overlapping expression domains of Dlx-2 and Dlx-3 suggest distinct roles for distal-less homeobox genes in craniofacial development. Mech Dev 48:199–215.[CrossRef][Medline] [Order article via Infotrieve]
• Ryu OH, Hu JC, Yamakoshi Y, Villemain JL, Cao X, Zhang C, et al. (2002). Porcine kallikrein-4 activation, glycosylation, activity and expression in procaryotic and eukaryotic hosts. Eur J Oral Sci 110:358–365.[CrossRef][Medline] [Order article via Infotrieve]
• Salido EC, Yen P, Koprivnikar K, Yu L-C, Shapiro L (1992). The human enamel protein gene amelogenin is expressed from both the X and Y-chromosomes. Am J Hum Genet 50:303–316.[Medline] [Order article via Infotrieve]
• Scherer SW, Heng HHQ, Robinson GW, Mahon KA, Evans JP, Tsui L-C (1995). Assignment of the human homolog of mouse Dlx3 to chromosome 17q21.3-q22 by analysis of somatic cell hybrids and fluorescence in situ hybridization. Mamm Genome 6:310–311.[CrossRef][Medline] [Order article via Infotrieve]
• Schroeder HE (1992). Oral structure biology. New York: Thieme.
• Sekigushi H, Kiyoshi M, Yakushiji M (2001a). DNA diagnosis of X-linked amelogenesis imperfecta using PCR detection method of the human amelogenin gene. Dent Jpn 37:109–112.
• Sekigushi H, Alaluusua S, Minaguchi K, Yakushui M (2001b). A new mutation in the amelogenin gene causes X-linked amelogenesis imperfecta (abstract). J Dent Res 80:617.
• Seyer JM (1972). Bovine enamel proteins. In: The comparative molecular biology of extracellular matrices. Slavkin HC, editor. New York: Academic Press, pp. 273–295.
• Simmer JP (1995). Alternative splicing of amelogenins. Connect Tissue Res 32:131–136.[Medline] [Order article via Infotrieve]
• Simmer JP, Fincham AG (1995). Molecular mechanisms of dental enamel formation. Crit Rev Oral Biol Med 6:84–108.[Abstract/Free Full Text]
• Simmer JP, Hu JC (2002). Expression, structure, and function of enamel proteinases (review). Connect Tissue Res 43:441–449.[Medline] [Order article via Infotrieve]
• Simmer JP, Fukae M, Tanabe T, Yamakoshi Y, Uchida T, Xhu J (1998). Purification characterization and cloning of enamel matrix serine proteinase 1. J Dent Res 77:377–386.
• Simmer JP, Ryu OH, Qian Q, Zhang C, Cao X, Sun X, et al. (2000). Cloning and characterization of a cDNA encoding Human EMPS1. In: Chemistry and biology of mineralized tissues. Proceedings of the Sixth International Conference, 1998. Goldberg M, Robinson C, editors. Vittel, France: American Academy of Orthopedic Surgeons, pp. 205–208.
• Simmons D, Gu TT, Krebsbach PH, Yamada Y, MacDougall M (1998). Identification and characterization of a cDNA for mouse ameloblastin. Connect Tissue Res 39:3–12; discussion 63–67.[Medline] [Order article via Infotrieve]
• Snead ML, Lau EC, Zeichner-David M, Fincham AG, Woo SL, Slavkin HC (1985). DNA sequence for cloned cDNA for murine amelogenin reveals the amino acid sequence for enamel specific protein. Biochem Biophys Res Commun 129:812–818.[CrossRef][Medline] [Order article via Infotrieve]
• Stephenson SA, Veriky K, Ashworth LK, Clements JA (1999). Localization of a new prostate-specific antigen-related serine protease gene, KLK4, is evidence for an expanded human kallikrein gene family cluster on chromosome 19q13.3–13.4. J Biol Chem 274:23210–23214.[Abstract/Free Full Text]
• Takata T, Zhao M, Uchida T, Wang T, Aoki T, Bartlett JD, et al. (2000). Immunohistochemical detection and distribution of enamelysin (MMP-20) in human odontogenic tumors. J Dent Res 79:1608–1613.
• Tanabe T (1984). Purification and characterization of proteolytic enzymes in immature porcine enamel. Tsurumi Shigaku 10:443–452.[Medline] [Order article via Infotrieve]
• Tanabe T, Aoba T, Moreno EC, Fukae M, Shimizu M (1990). Properties of phosphorylated 32-kDa non-amelogenin proteins isolated from porcine secretory enamel. Calcif Tissue Int 46:205–215.[Medline] [Order article via Infotrieve]
• Toyosawa S, Fujiwara T, Shintani S, Sato A, Ogawa Y, Sobue S, et al. (2000). Cloning and characterization of the human ameloblastin gene. Gene 256:1–11.[CrossRef][Medline] [Order article via Infotrieve]
• Uchida T, Tanabe T, Fukae M, Shimizu M (1991a). Immunocytochemical, immunochemical detection of a 32-kDa non-amelogenin and related proteins in porcine tooth germ. Arch Histol Cytol 54:527–538.[Medline] [Order article via Infotrieve]
• Uchida T, Tanabe T, Fukae M, Shimizu M, Yamada M, Miake K, et al. (1991b). Immunochemical and immunohistochemical studies, using antisera against porcine 25-kDa amelogenin, 89-kDa enamelin and the 13-17 kDa non-amelogenins, on immature enamel of the pig and rat. Histochemistry 96:129–138.[CrossRef][Medline] [Order article via Infotrieve]
• Uchida T, Fukae M, Tanabe T, Yamakoshi Y, Satoda T, Murakami C, et al. (1995). Immunochemical and immunocytochemical study of a 15-kDa non-amelogenin and related proteins in the porcine immature enamel proposal of a new group of enamel proteins ‘sheath proteins’. Biomed Res 16:131–140.
• Uchida T, Murakami C, Dohi N, Wakida K, Satoda T, Takahashi O (1997). Synthesis, secretion, degradation, and fate of ameloblastin during the matrix formation stage of the rat incisor as shown by immunocytochemistry and immunochemistry using region-specific antibodies. J Histochem Cytochem 45:1329–1340.[Abstract/Free Full Text]
• Väänänen A, Srinivas R, Parikka M, Palosaari H, Bartlett JD, Iwata K, et al. (2001). Expression and regulation of MMP-20 in human tongue carcinoma cells. J Dent Res 80:1884–1889.
• von Heijne G (1990). The signal peptide (review). J Membr Biol 115:195–201.[CrossRef][Medline] [Order article via Infotrieve]
• Weiss K, Stock DW, Shao Z (1998). Dynamic interactions and the evolutionary genetics of dental patterning. Crit Rev Oral Biol Med 9:369–398.[Abstract/Free Full Text]
• Witkop CJJ (1988). Amelogenesis imperfecta, dentinogenesis imperfecta and dentin dysplasia revisited problems in classification (review). J Oral Pathol 17:547–553.[CrossRef][Medline] [Order article via Infotrieve]
• Wright JT, Hart PS, Aldred MJ, Seow K, Crawford PJM, Hong SP, et al. (2003). Relationship of phenotype and genotype in X-linked amelogenesis imperfecta (review). Connect Tissue Res 44(Suppl 1):72–78.[CrossRef][Medline] [Order article via Infotrieve]
• Yamada Y, Yamakoshi Y, Gerlach RF, Hu JC-C, Liu S, Bartlett JD, et al. (2003). Purification and characterization of enamelysin from secretory stage pig enamel. Arch Comp Histol Tooth Form 8:21–27.
• Yamakoshi Y, Tanabe T, Fukae M, Shimizu M (1994). Porcine amelogenins. Calcif Tissue Int 54:69–75.[CrossRef][Medline] [Order article via Infotrieve]
• Yamakoshi Y, Pinheiro FH, Tanabe T, Fukae M, Shimizu M (1998). Sites of asparagine-linked oligosaccharides in porcine 32-kDa enamelin. Connect Tissue Res 39:39–46; discussion 63–67.[Medline] [Order article via Infotrieve]
• Yamakoshi Y, Tanabe T, Oida S, Hu CC, Simmer JP, Fukae M (2001). Calcium binding of enamel proteins and their derivatives with emphasis on the calcium-binding domain of porcine sheathlin. Arch Oral Biol 46:1005–1014.[CrossRef][Medline] [Order article via Infotrieve]
• Zeichner-David M, Vides J, MacDougall M, Fincham AG, Snead ML, Bessem C, et al. (1988). Biosynthesis and characterization of rabbit tooth enamel extracellular matrix proteins. Biochem J 251:631–641.[Medline] [Order article via Infotrieve]

Journal of Dental Research, Vol. 84, No. 12, 1117-1126 (2005)
DOI: 10.1177/154405910508401206


CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    Twitter    What's this?

This article has been cited by other articles:

				M. J. Barron, S. J. Brookes, J. Kirkham, R. C. Shore, C. Hunt, A. Mironov, N. J. Kingswell, J. Maycock, C. A. Shuttleworth, and M. J. Dixon A mutation in the mouse Amelx tri-tyrosyl domain results in impaired secretion of amelogenin and phenocopies human X-linked amelogenesis imperfecta Hum. Mol. Genet., January 27, 2010; (2010): ddq001v2 - ddq001. [Abstract] [Full Text] [PDF]

				O. Golonzhka, D. Metzger, J.-M. Bornert, B. K. Bay, M. K. Gross, C. Kioussi, and M. Leid Ctip2/Bcl11b controls ameloblast formation during mammalian odontogenesis PNAS, March 17, 2009; 106(11): 4278 - 4283. [Abstract] [Full Text] [PDF]

				B. Ruhin-Poncet, S. Ghoul-Mazgar, D. Hotton, F. Capron, M. H. Jaafoura, G. Goubin, and A. Berdal Msx and Dlx Homeogene Expression in Epithelial Odontogenic Tumors J. Histochem. Cytochem., January 1, 2009; 57(1): 69 - 78. [Abstract] [Full Text] [PDF]

				K. Kawasaki and K.M. Weiss SCPP Gene Evolution and the Dental Mineralization Continuum Journal of Dental Research, June 1, 2008; 87(6): 520 - 531. [Abstract] [Full Text] [PDF]

				X. J. Fu, K. Nozu, K. Goji, K. Ikeda, I. Kamioka, T. Fujita, H. Kaito, H. Nishio, K. Iijima, and M. Matsuo Enamel-renal syndrome associated with hypokalaemic metabolic alkalosis and impaired renal concentration: a novel syndrome? Nephrol. Dial. Transplant., October 1, 2006; 21(10): 2959 - 2962. [Full Text] [PDF]

This Article Abstract Figures Only Free Full Text (Free PDF) Free Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Saved Citations Download to citation manager Request Permissions Request Reprints Add to My Marked Citations Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Citing Articles via Scopus Google Scholar Articles by Stephanopoulos, G. Articles by Lyroudia, K. Search for Related Content PubMed PubMed Citation Articles by Stephanopoulos, G. Articles by Lyroudia, K. Pubmed/NCBI databases Substance via MeSH Genetics Home Reference Genetics Home Reference - amelogenesis imperfecta Genetics Home Reference - AMELX Gene Genetics Home Reference - ENAM Gene Genetics Home Reference - MMP20 Gene Social Bookmarking                         What's this?