Meeting Abstract
P1.63 Monday, Jan. 4 Development of the chick costal joint WINSLOW, B. B.*; BURKE, A. C.; Wesleyan University; Wesleyan University bwinslow@wesleyan.edu
The development of synovial (diarthrodial) joints appears to be largely conserved between species and across anatomical locations. Synovial joints are thought to develop by segmentation of cartilaginous condensations, followed by cavitation to form a joint capsule. The site of segmentation is termed the interzone. Molecular control of interzone formation and cavitation has been described in limb and jaw joints. Interzone formation involves loss of cartilage specific gene expression and up regulation of Gdf5, Barx1, Bapx1, Chordin, Autotaxin, and other genes regulated by Wnt14/9a. Later, Cd44 is expressed in the interzone, and is involved in cavitation. We are interested in the development of the costal joint, a synovial joint found in the ribs of avians. The costal joint forms between the vertebral and sternal elements of the rib, and is morphologically similar to the widely studied interphalangeal joints. Despite this morphological similarity, we have found significant differences in the development of the chick costal joint and the metatarsophalangeal joint, specifically in interzone formation. The avian vertebral and sternal rib condensations are distinct and label with alcian blue by stage HH28, though Sox9 expression is continuous between the condensations. The alcian blue labeled condensations merge around HH30. Collagen II expression is never continuous between the elements. An interzone forms by HH34, and cavitation occurs by HH39, preceded by Cd44 expression, similar to other joints. Surprisingly, Wnt14/9a, Gdf5, Barx1, and Chordin are absent from the interzone of the avian costal joints at HH36. Autotaxin is expressed in the interzone, and Bapx1 is expressed by the surrounding cartilage. These data suggest that while cavitation appears similar to other synovial joints, an alternative molecular mechanism is involved in costal joint interzone formation.
