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Presumptive primordial germ cells (pPGCs) were examined during migration from their deep endodermal position to the endodermal crest in Xenopus laevis, using light and electron microscopy with Epon sections, and several morphological characteristics of pPGCs, associated with their migration, were revealed. pPGCs displayed polymorphism, with smooth contours. The intercellular space around the pPGCs was large and variable in width and cytoplasmic processes from pPGCs were occasionally observed in it. It was shown quantitatively that pPGCs at the migratory stage had a tendency to move with the leading end, towards which the nucleus was localized, dragging the germinal plasm behind. These polarized pPGCs were frequently associated with large intercellular spaces, both at their leading and trailing ends. Cytoplasmic processes of polarizing pPGCs found in the large intercellular space at the leading end were conspicuous. Ultrastructurally, the nuclei of pPGCs were euchromatic, and the nucleolus was prominent. The germinal plasm at the light microscope level corresponded to the cytoplasmic area near the nucleus where a large number of mitochondria with well-developed cristae and most of the other organelles were aggregated. Centrioles and centriole-associated microtubules observed in the aggregate were thought to be important structures responsible for the cell polarization mentioned above. It was demonstrated quantitatively that the size of mitochondria in pPGCs was larger on average than that of mitochondria in neighbouring somatic endodermal cells. Numerous irregularly shaped small yolk platelets characterized pPGCs. These ultrastructural features suggested that pPGCs were in an activated metabolic state. It was concluded that the migration of pPGCs was attributable to active movement with high cell metabolism, causing the formation of cell processes and intracellular polarization.

In this study the histochemical immunoperoxidase method was adopted t o clarify the localization of prolactin (PRL) in the decidua and villus of normal, aborted, and molar pregnancy and choriocarcinoma. After evacuation and curettage or operative resection, tissue specimens were fixed in formalin solution and emb,edded in paraffin. Some frozen sections were made after fixation by Zamboni's solution. The indirect immunoperoxidase method was used. Anti-PRL antibody was donated by NIAMDD and was used after absorption by hPL. Results showed that: (1) In normal pregnancy, PRL is located in syncytiotrophoblast cells. (2) In spontaneous abortion, PRL is detected in syncytiotrophoblast cells, despite fetal death, provided that hCG continues to be produced. (3) In molar pregnancy, PRL is localized in syncytie trophoblast cells, even those which penetrate into the decidua. (4) In choriocarcinoma, PRL is located ih the cancer cells.We concluded that syncytiotrophoblast cells are the main site of PRL as long as trophoblast cells are alive and active.

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