Transport of Proteins Across the Fetal Membranes

The zygote nucleus comes into being in an environment of maternal proteins comprising the cytoplasm of the fertilized egg. Many of these proteins are potentially antigenic for the new organism, in the sense that were they administered parenterally during adult life they would induce an immune response. Yet the zygote nucleus must operate in this immunologically incompatible environment and initiate the synthesis of all those proteins which will characterize the new organism. During development these proteins will dilute, and finally displace, those of maternal origin. Metabolic utilization will result in loss of maternal, as well as fetal, protein. Nevertheless traces of the specifically maternal proteins will persist as such for a long period. Their final disappearance, as distinct from their dilution, may be brought about by processes of transamination resulting in their being remodeled on the zygote pattern and so incorporated in the new individual, or by immunological reactions...