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Epithelial-Mesenchymal Transformation during Craniofacial Development

¹ Graduate Endodontics Department and
² Biomedical Sciences Department, Texas A&M University System, Baylor College of Dentistry, 3302 Gaston Ave., Dallas, TX 75266, USA;

View larger version (51K): [in this window] [in a new window]   Figure 1. Comparison of cranial neural crest and palate EMT. Cranial neural crest (CNC) is derived from a single layer of epithelial cells located at the transition zone between neuroepithelium and surface ectoderm (Weston et al., 2004). The cells have increased Slug, and decreased Sox2 expression. The cells lose cell-cell adhesion molecules [(N-cam or E-Cadherin (E-Cad)] and increase actin (RhoB) and extracellular matrix remodeling (Mmp2) proteins and growth factor receptors (PdgfR). After the crest cells have moved away from the neuroepithelium, they increase expression of the HNK-1 epitope (Del Barrio and Nieto, 2004). Palate EMT requires several more steps than CNC, since the periderm cells are sloughed through apoptosis, two epithelial sheets fuse at the apical membranes, and some cells may move to the oral or nasal epithelium. The cells increase Snail, Tgfβ3 signal transduction through Smad2, PI-3 kinase, and MMP, while decreasing E-cadherin. In both tissues, cell adhesion proteins are repressed, and matrix degradation and mesenchymal or tissue-specific proteins are increased. A confocal image of a single optical plane through palatal MEE cells that were labeled with CCFSE and then cultured for 72 hrs demonstrates the extensive remodeling at the seam as cells undergo EMT.

View larger version (37K): [in this window] [in a new window]   Figure 2. Experimental models for the study of EMT. (A) Embryonic mouse palatal shelves were dissected from the 12.5-gestational-day mouse embryos. (B) The palatal shelves are in the horizontal position, but are not touching or fused at this stage. (C) The dissected palatal shelves were placed in organ culture on a filter at the air-media interface for 20 to 72 hrs in the static organ culture model (Kang and Svoboda, 2002). (D) The palatal region can also be cultured in suspension cultures. The palatal region was dissected by a horizontal incision made through the oral opening (A - solid line), and the upper part of the head was resected by a second incision made parallel to the first at the level of the eyes (dashed lines in A and dashed line in B). The tongue and brain tissue were removed from the explants. The palatal explants were placed in 50-mL penicillin bottles (n = 3 to 6 explants/bottle) on a roller bottle culture system (Shiota et al., 1990; Chou et al., 2004). In this system, the palatal shelves fuse in 24 hrs.

View larger version (69K): [in this window] [in a new window]   Figure 3. Five stages of palatal fusion in vitro as observed from confocal analysis of whole-mount palates stained with CCFSE (A–E), H&E staining (F-J), and laminin immunohistochemical studies (K-O) (Kang and Svoboda, 2002). Characteristics of each stage in the 3 morphological formats are explained in Table 1. Scale bars = 200 µM in A-E and 160 µM in F-O. (P) Mean fusion scores of palates after 72 hrs of culture in controls and LY294002 treatment groups. There was no significant difference between controls and 100 M LY294002-treated tissues. However, the 1- and 10-µM LY294002-treated palates were significantly different from controls (p 0.01).

Journal of Dental Research, Vol. 84, No. 8, 678-690 (2005)
DOI: 10.1177/154405910508400801


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