Autonomous Differentiation of the Head Region in Chick Embryos

The growth and differentiation of the presumptive head region in chick embryos has been studied. In amniote embryos, the head forms from a small region of epithelium immediately anterior to the notochord. This area, referred to as the prechordal plate, is thought to be under instructive signaling influences emanating from the underlying endoderm that ultimately dictates the morphogenesis and cytodifferentiation of cells of the head. However, it is not known how cell interactions in the prechordal plate lead to morphogenesis of head tissues. In this study, presumptive head regions from very early chick embryos were cultured in isolation for periods of 24-48 hours. The cultures were cryosectioned and probed with fluorescently labeled monoclonal antibodies to reveal specific patterns of adhesion molecules and extracellular matrix molecules. Images of the cultures were digitized with peltier-cooled photomicroscopy in order to detect the expression of various extracellular matrix and cell surface adhesion molecules known to influence the differentiation of cell types during development. We have found that the expression pattern of chondroitin sulfate can be correlated to autonomous head development in culture. Furthermore, expression pattern of N-cadherin in these cultured heads suggests a synergistic mechanism of extracellular effects that may determine cellular mechanisms of head development in the normal embryo. Taken together with the expression of genes during early chick development, this study suggests the head develops autonomously and independent of the embryonic axis