Figure 2: G_sα ablation does not affect chondrocyte proliferation but accelerates differentiation and apoptosis.

Tamoxifen was administrated at 3 days of age and growth plates were analysed 9 (a–d) and 13 (e–h) days later. Chondrocyte proliferation was not affected (a, pink cells, BrdU labelling for 2 hours), but post-mitotic flat cells were missed in G_sα cKO mice (depicted by yellow dotted line). Increase in the TUNEL-positive cells was observed at the chondro–osseous junction in G_sα cKO mice as compared with controls (b, green cells). At the same time, elevated numbers of cells expressing collagen type X mRNA (c) and Indian Hedgehog mRNA (d) were observed in G_sα cKO mice as compared with controls. (e) BrdU-positive chondrocytes (brown) were observed throughout the growth plate of G_sα cKO mice 13 days after gene ablation. Sections were counterstained with Eosin (pink) and Alcian Blue (blue). (f) TUNEL-positive cells (green) were detected mainly at the metaphyseal side of the growth plate but also at the epiphyseal side and in the middle of the growth plate 13 days after gene ablation. (g) Collagen type X mRNA (pink) was detected in the middle of the growth plate in G_sα cKO mice at this time point. (h) There was no increase in osteoclast activity in G_sα cKO mice as detected by TRAP staining. Dotted lines depict growth plates. f=flat cell layer; h=hypertrophic layer. Arrows show typical apoptotic chondrocytes. ep=epiphyseal bone. Scale bars, 100 μm.