Expression patterns of Sox9, CbfaI and Osteocalcin. In situ hybridizations were done on sections of heads from nontransgenic (NT) and FGF9 transgenic mice using [35S]-labeled riboprobes for Sox9 (A-F'), CbfaI (G-H') and osteocalcin (I-J'). Panels A-J are bright field images and panels A'-J' are the corresponding dark-field images. Expression of Sox9 is induced in the cranial mesenchymal cells of the FGF9 transgenic mice by E13 (D'). Sox9 expression is detected in the ventricular regions of the brain at E13 in both the transgenic and nontransgenic mice (C', D'). CbfaI and osteocalcin are expressed in the differentiating calvarial osteoblasts (os) of nontransgenic mice at E15 (G', I') but not in the skulls of the FGF9 transgenic mice (H', J'). Scale bar: 50 μm in G-J'; 100 μm in A-F'.