Fig. 4. Col2a1-ICAT transgenic mice have delayed appearance of the secondary ossification center (SOC) and altered growth plate morphology. (A) Development of the growth plate in postnatal mice was analyzed by histology staining with Alcian Blue/Hemotoxylin and Orange G. In WT mice, the formation of epiphysal SOC was initiated at 1 week of age and was well developed at age 2 weeks. Col2a1-ICAT transgenic mice display an obvious delay in the formation of SOC at 1 and 2 weeks of age. (B) Tissue sections stained with Safranin O and Fast Green show that the length of both the proliferating and hypertrophic zones was reduced in 2-week-old Col2a1-ICAT transgenic mice. The hypertrophic chondrocyte columns were disorganized in Col2a1-ICAT transgenic mice. (C-F) Histomorphometric measurements show that the (C) distance from articular surface to hypertrophic zone, (D) growth plate length, and the (E,F) lengths of the proliferating (E) and hypertrophic (F) zones are significantly decreased in 2-week-old Col2a1-ICAT transgenic mice compared with their WT littermates. ^*P<0.05, unpaired t-test, n=6.