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Histo-cytochemical characteristics of primordial germ cells in human embryos.

The histo-cytochemical characteristics of primordial germ cells (PGCs) in early human embryos were investigated in conjunction with identification of the cells. Employing the periodic acid-Schiff (PAS) reaction, PGCs in the migration stage or in the early settlement stage were clearly distinguished from somatic cells by their content of PAS-positive intracytaplasmic glycogen. The alkaline phosphatase (ALPase) reaction was confirmed to represent a useful method for identifying PGCs throughout their endodermal to settlement stages. The enzyme activity was detectable on the plasma membrane of PGCs, especially in parts associated with other adjacent cells, and also on the outer membrane of mitochondria, the Golgi apparatus and the nuclear envelope of PGCs. Histochemically, the ALPase of PGCs revealed heat-lability and inhibition by levamisole, suggesting that the isozyme was of the liver type. Using the colloidal iron reaction, acid mucin was demonstrated on the surface of PGC which was alcianophilic. This indicated that the plasma membrane of PGC is composed of acid mucin including sialic acid, and also that this method is applicable to the identification of PGCs.