The Role Of Fibronectin In The Interstitial Migration Of Primordial Germ-Cells In Amniotes

Primordial germ cells (PGCs) in amniotes separate from the endoderm of the early embryo and finally migrate through the dorsal mesentery (DM), which is the last portion of the migratory pathway, into the gonadal anlage, while in birds and some reptiles, the cells temporarily circulate via the blood vascular system before undergoing this migration. To understand the role of extracellular matrix in the migration of PGCs, the distribution and localization of fibronectin (FN) were examined using direct immunoperoxidase staining in embryos of mice, chicks and man. In mouse embryos of 10.0 to 11.0 days of gestation, the DM was rich in FN, at which time the PGCs were at the peak of their migration. FN was localized at the sites of interaction between cytoplasmic processes of PGCs and the neighboring somatic cells. In man, a positive reaction to FN was found in the DM of 5-week old embryos, in which most of PGCs were migrating. In chick embryos at 2.5 days of incubation, the splanchnic mesoderm (SPM), into which the PGCs were passing from the blood vessels, was rich in FN. In 3.0-day-embryos, the DM, which was derived from the SPM, was rich in FN. FN was localized at the sites of interaction between pseudopodia of PGCs and the adjacent somatic cells. After the completion of PGC migration into the gonad, FN reaction was weakened or disappeared in every species examined. These results indicate that fibronectin plays a significant role in the interstitial migration of PGCs.