Embryological Development of Primordial Germ-cells in the Mouse: Influence of a New Mutation, Wj

Twenty-seven mouse embryos at days from matings of Wjw × Wjw were examined in order to establish the embryological basis of the germ-cell deficiency found in the WjWj genotype at birth. Elective staining of primordial germ-cells was obtained with the azo dye coupling histochemical technique for alkaline phosphatase. Numbers and locations of these cells were recorded in complete serial sections. Formation of germ-cells occurs, as in normals, in all members of the 8-day group. At 9 days and later, during gonial migration from yolk sac toward germinal ridges, two distinct populations of individuals are recognizable. In one, the number of germ-cells increases; in the other, totals remain very low. The latter would be expected to characterize the WjWj class. Observed incidence of such cases was close to the theoretical frequency of 25 per cent, defective offspring. These findings support the earlier proof (Mintz & Russell, 1955, 1957) that the cells observed are the primordial germ-cells and are of extra-gonadal origin. In defectives, migratory retardation of germ-cells accompanies their mitotic insufficiency. The effects of Wj are compared with those of the alleles W and Wv, and the significance of the study for the problem of pleiotropic gene action is considered.