LOCALIZATION OF ALPHA-FETOPROTEIN DURING THE FORMATION OF THE NEURAL-TUBE AND SOMITES IN CHICK-EMBRYO

Very little is known about the biological role of alpha-fetoprotein (AFP) in normal development. This study was undertaken to look for AFP-positive tissues involved in active morphogenetic and histogenetic events. Using a polyclonal antibody specific for AFP and the immunoperoxidase technique, we have studied the AFP localization during the formation of the neural tube and somites in chick embryo. Immunostaining of early whole embryos, cephalic fold stage, shows a strong immunoreaction for AFP in the cephalic and neural folds. In a more advanced stage of the development (6-somite stage), the AFP expression has followed the caudal direction of the neural fold forming process. Immunostaining of 6- and 9-somite embryo sections shows an increase of AFP expression from the most undifferentiated (the neural fold), to the most differentiated (the neural tube). AFP does not label the nonsegmented paraxial mesoderm, from which the somite is derived. Instead, when the paraxial mesoderm is segmented and has formed a somite, AFP positive cells are detected in the somite. The morphological differentiation of somite is joined to one biochemical differentiation, since the myotome and sclerotome cells are AFP positive while the dermatome cells are AFP negative. The sclerotome cells become AFP negative when they surround the notochord to form the vertebral body. The results presented here strongly suggest a close association of AFP with cell proliferation and differentiation.