Fig. 1. Expression of chick Nkx3.2 is restricted to immature proliferative chondrocytes during endochondral bone development. Chick embryos, stages as indicated, were pulse labeled with BrdU before harvesting and processing for section in situ hybridization (ISH; A-J) or stained with an anti-BrdU antibody (K,L). Arrowheads indicate approximate boundary of BrdU-positive zone in parallel sections. Arrows (A-F) indicate distal-most boundary of cartilage, marked by col IX and Sox9 expression.