Germ cell migration in toad (Bufo bufo): effect of ventral grafting of embryonic dorsal regions

Bufo bufo embryos were used at the tail-bud stage for the grafting of two different dorsal regions (cephalic and caudal tracts) into the ventral side of the embryo (cf. Fig. 1). Germ cell localization was studied at the beginning of larval life. The results seem to confirm the original finding of Gipouloux (1970) who suggested that in anurans germ cells migrate under the attraction of a substance produced by the dorsal mesodermal tissues. The attractive action of dorsal tissue was confined to the caudal region of the embryo. In operated specimens the migration of germ cells was drastically altered. The genital ridges of host embryos were almost sterile, while numerous germ cells appeared associated with caudal grafts. A considerably smaller number of germ cells was associated with cephalic grafts. About 80% of germ cells associated with caudal grafts were present at the same levels where a well-developed dorsal mesentery was also present. It is suggested that the formation of the dorsal mesentery plays a morphogenetic role in segregating primordial germ cells from other endodermal cells and contributes to their final localization in the genital ridges.