03-P067 The control of convergent-extension movements in a tubular epithelium

islands in the extraembryonic yolk sac. This observation has led to the hypothesis that both cell types originate from a common precursor known as the hemangioblast. This hypothesis has been supported mainly by the co-expression of several genes in both cell types and by in vitro differentiation studies. However, recent studies indicate that primitive blood cells originate from an intermediate population of hemogenic endothelial cells. Chick Cerberus gene (cCer) codes for a secreted factor expressed in the anterior mesendoderm that gives rise to blood islands, among other tissues. During the study of cCer transcriptional regulation in chick embryos, we isolated a short cis-regulatory region that is able to drive reporter gene expression specifically in blood island precursor cells or hemangioblasts. We have been using this hemangioblast-specific reporter construct (Hb-eGFP) to characterise the gene expression profile of the chick hemangioblast and to track the origin and fate of hemangioblasts in living embryos. Here, we will present data on the gene expression profile of the early chick hemangioblast as well as on the dynamics of blood island morphogenesis and differentiation.