Expression patterns of Col2a1, Col10a1 and Ihh. In situ hybridizations were done on sections of heads from nontransgenic (NT) and FGF9 transgenic mice using [35S]-labeled riboprobes for Col2a (A-H'), Col10a1 (I-J') and Ihh (K-L'). Panels A-L are bright field images and panels A'-L' are the corresponding dark-field images. Expression of Col2a1 is enhanced in the cranial mesenchymal cells of the FGF9 transgenic mice by E15 (B') and is decreased in some cells by P7 (H'). Hybridizations performed on adjacent sections show expression of Col10a1 in these hypertropic (hyp) chondrocytes (J'). Ihh expression was detected in the differentiated chondrocytes by P7 (L'). Abbreviations: b, brain; ch, chondrocytes; hyp, hypertropic chondrocytes; os, osteoblasts; s, skin. Scale bar: 100 μm in A-L'.