Fig. 4. Pax1 induces Bapx1 expression and chondrogenesis in explants of chick PSM. Explants of PSM isolated from stage HH10 chick embryos were infected with the control RCAS-A-AP retrovirus (AP; A, lanes 1,3; B, lane 1) or with the RCAS-A-Pax1 retrovirus overexpressing mouse Pax1 (A, lanes 2,4; B, lane 2), and cultured in the absence (A, lanes 1,2; B) or the presence (A, lanes 3,4) of 500 ng/ml Shh. After 5 days of culture, explants were harvested and analyzed by RT-PCR. The PCR products for chick Bapx1, aggrecan, Gapdh and mouse Pax1 are shown.