The removal of the exon 2 of Tgfbr2 in articular chondrocytes of mouse knee joints. A: Before the Cre-recombination, a size of 1-kb PCR product is generated by the primers Tgfbr2-F4 and Tgfbr2-R and after the Cre-recombination, a size of 608-bp PCR product is generated by the primers Tgfbr2-F and Tgfbr2-R. B: Cells with intense X-gal staining (blue color) appear above the tidemark (dashed line) of the articular cartilage of knee joints in AgcCreERT2+/−,Rosa26+/floxlacZ mice at 2 months of age. A counterstain was performed with Safranin O staining of proteoglycan. C: Every articular chondrocyte in AgcCreERT2+/−;Tgfbr2+/+ littermates contains the exon 2 of Tgfbr2. However, <14% of articular chondrocytes with the exon 2 of Tgfbr2 are observed in the conditionally Tgfbr2-knockout mice. Significant difference was found in the number of the exon 2 of the Tgfbr2 cells between the two groups, ∗∗P < 0.01 (t-test).