Movement of Primordial Germ Cells in the Endodermal Cell Mass of Xenopus Embryos

In Xenopus embryos, primordial germ cells (PGC), located ventrally in the endoderm, migrate into dorsal endodermal crest where they exit from the endoderm and migrate into genital ridges. The aim of this study was to investigate the nature of PGC movement from ventral to dorsal endoderm. A grafting experiment was planned in which theventral part of one of three endodermal regions - anterior, middle or posterior endoderm labelled with fluorescein dextran amine (FDA) from stage 28 donor embryos was grafted to a similar position in unlabelled host embryos of the same stage. The grafted embryos were allowed to develop until stage 40 and 46 when they were examinedhistologically for presence of FDA positive cells. Regardless of some slight local distortion (especially in the anterior graft), labelled endodermal cells appeared as a cohesive group in the ventral region adherent to the ventral lateral plate mesoderm. In all cases there weresharp, straight, anterior, posterior and dorsal boundaries between the donor labelled cells and host endoderm. These results suggest that, there are no early endodermal cell movements, either as single cells or as a group of cells, involved in morphogenesis of the endoderm, indicating that the PGC could move actively through the endoderm.