A Possibility of an in Vitro Differentiation of Primordial Germ Cells (PGCs) from Blastomeres Containing "Germinal Plasm" of Early Cleavage Stage in Xenopus laevis. (xenopus laevis/"germinal plasm"/germinal granule/PGCs)

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Abstract
The blastomeres containing the germinal plasm were isolated from 32-cell stage Xenopus embryos and cultured in vitro for various periods of time until the control embryos developed to stage 28, 33/34, 40 and 45, respectively. The cells containing the plasm in the stage-28, 33/34 and 40 explants were similar in external shape and in distribution in the spherical endodermal cell mass to the presumptive primordial germ cells (pPGC) in normal embryos of the corresponding stages. Cells in explants and the pPGC were separated by a large intercellular space from the surrounding endodermal cells. The change in proportion of the compact or the loosely structured germinal granules and the irregularly shaped-stringlike bodies (ISB) occurred in the cells of the explants with prolongation of the culture period. In cells of the stage-45 explant and in the PGC of normal stage-45 tadpoles, the ISB and granular materials replace those germinal granules. The change of the germinal granules through the ISB to the granular materials, noticed in the normal course of differentiation of pPGC into PGC, also takes place in the cells of the explants during the culture. Cells in the explants are genuine pPGC or PGC. This is the 1st demonstration of a possibility of in vitro differentiation of PGC from the blastomeres containing the germinal plasm of early cleavage stage.