The patterns of expression of C-KIT and PCTAIRE-1 were similar, with a reduction in the proportion of positive germ cells in 17- to 19-wk samples compared to less mature samples. Mice that lack a functional C-KIT receptor contain less germ cells because of reduced survival of migratory PGCs; it is assumed that expression of C-KIT is also essential for PGC migration in humans, which would be consistent with detection of the protein on the surface of the OCT4-positive germ cells. Studies in rats have demonstrated that the kit ligand is a prosurvival factor for germ cells, and expression of C-KIT by human fetal germ cells may contribute to their survival.
Detection of MAGE-A4 in fetal germ cells was associated with the appearance of groups of cells at the periphery of the cords.
The variable pattern of expression of putative germ cell markers in the tissues that we examined prompted us to determine whether this might be correlated with germ cell morphology. Data published 20-30 yr ago, in which germ cell morphology was determined by electron microscopy, had described a variety of germ cell types.