Figure 2. Oligonucleotide primers to prepare for RNA probes (upper). RNA polymerases and restriction enzymes used for RNA probes (middle). In situ hybridization for COL I (a-d) and COL III (e-h) during root formation and eruption of maxillary first molars (lower). (a,e) Week 2. (b,c,f,g) Week 4. (d,h) Week 6. Arrowheads in (c) and (g) indicate hybridization signals. B, alveolar bone; P, periodontal ligaments; C, cementum; D, dentin. Bars = 10 µm (a,e); 20 µm (b,d,f,h); 5 µm (c,g).