Somite Centers and their role in Somitogenesis in chick embryo (Gallus gallus domesticus)

Abstract

Abstract Spratt and Condon (1947) reported that the material from which the somites are formed lies in and close to the primitive streak. They described that area to be 0.13-0.30 mm. behind the pit of the definitive streak and head process blastodenn. In 1955, Spratt believed that there are two somite centers: one on each side of the posterior half of the node. Each center was found to extend about 0.05-0.02 mm. under the node and 0.2-0.25 lateral to it. In this study, thirty six chick embryos of definitive primitive streak stage were used to see the effect of surgical removal of the assumed somite centers on somitogenesis. Embryos were cultured in vitro using New’s technique. An incision was made on the cndoderm on both sides using cactus needle and the areas where the assumed somite centers were lying were removed on both sides. The embryos were then further incubated for Eight Hours followed by fixation in Bouin’s fluid, cleared in oil of cedar wood followed by photography, and studied as whole mount. The results showed that the paraxial mesoderm was normally segmented on both sides. In the opinion of the somite centers have no effect on the development of somites and reported that factors other than the somite centers are responsible for the process of somitogenesis in chick embryo. More support was given by. He reported the existence of bilateral chains consisting of bipolar cells originating fiom the caudal part of the prosencephalon and proceeding to the cranial aspect of the paraxial mesoderm on both sides. Experimental studies were performed and the results showed that the chains are critical to somite formation. It was concluded that factors other than the somite centers are involved in the process of somitogenesis in which embryo and in particular the chains of bipolar cells.