Figure 2. Buccal-lingual sections of the M1 in three-week-old rat stained with Azan (A-C) or treated for detecting GDF-5 (D,G), -6 (E,H), and -7 (F,I) transcripts. Small rectangles of B and C (A) indicate the areas enlarged in B and C, respectively. (B) Collagenous matrix fibers of acellular extrinsic fiber cementum are shown to be continuous with thick periodontal ligament fiber bundles extending obliquely from acellular cementum toward the alveolar bone (ab). (C) Cellular cementum is deposited on the root dentin surface near the apical end (arrows). Only scattered thin collagen fibers are seen in this region. (D-I) GDFs mRNA expression in regions B and C indicated in Fig. 2A. GDF-positive cells are widely distributed in the periodontal ligament, on the surfaces of the alveolar bone and the cementum (arrowheads). ab, alveolar bone; d, dentin; pdl, periodontal ligament; pul, pulp. Bar = 500 µm (A), 50 µm (B-I).