Localization of alpha-fetoprotein in developing chick amniotic membrane

The aim of this work was to investigate the localization of alpha-fetoprotein (AFP) in amniotic membrane (AM). By using the immunoperoxidase technique in several developmental stages, which reflected the changes of structure of the AM germinal layers, AFP was detected earliest in 7-day AM and localized selectively in the ectodermal cell layer. This was the only developmental stage at which AM occurred as a two-layer structure, ectoderm and somatic mesoderm, and was AFP-positive. In the zone of fusion of the AM with the inner wall of the allantoic sac, cystlike cavities were observed which were markedly immunoreactive to AFP. In those membranes where fusion had consolidated and a four-layer structure could be distinguished: ectoderm, somatic mesoderm, splanchnic mesoderm and endoderm, AFP was localized in the ectodermal cells and in the splanchnic mesoderm resulting from the inner wall of the allantoic sac. Both mesodermal layers could be distinguished by means of the AFP immunoreaction since AFP labelled the splanchnic, but not the somatic mesoderm. At later developmental stages, e.g. 18-day, the AM had a three-layer structure and AFP was localized selectively throughout the splanchnic mesoderm. The disappearance of the somatic mesoderm coinciding temporarily with the disappearance of AFP from the ectodermal cells, suggests that the presence of AFP in such cells could depend on some factors related to the somatic mesoderm.