PROLIFERATION AND MIGRATION OF PRIMORDIAL GERM-CELLS IN W-E W-E MOUSEEMBRYOS/

We have examined the numbers and distribution of primordial germ cells in W-e/W-e, W-e/+, and +/+ mouse embryos using Southern blotting to d etermine embryo genotypes. At early somite stages (5-7 somites: approx imately 81/2 days post coitum [dpc]) there are 50 to 100 germ cells in embryos of all genotypes. The number of perm cells in W-e/+ and +/+ e mbryos then beans to increase: at later somite stages (17-19 somites: approximately 91/2 dpc) they number about 200, and by 101/2 dpc there are approximately 725 W-e/+ and 850 +/+ germ cells. During this time, however, the number of germ cells in W-e/W-e embryos remains less than 100. At 81/2 dpc, the distribution of germ cells in the hindgut endod erm is the same in all genotypes. By 91/2 dpc, 30% of W-e/W-e germ cel ls are found in ectopic sites (allantois and vitelline artery); germ c ell distribution along the length of the hindgut appears normal, but g erm cells remain confined to the floor of the gut in W-e/W-e embryos, rather than being distributed around its circumference as in the other two genotypes. By 101/2 days, the migration of W-e/W-e germ cells thr ough the dorsal mesentery lags behind that of the other genotypes, and a larger proportion remains in the gut wall.