Changes in number, cell shape and adhesiveness induced by dopamine on chick primordial germ cells

Dopamine (DA), injected beneath the blastodisc of the chick embryo before the beginning of incubation, induced an approximately 2.5 times increase in the total number of primordial germ cells (PGCs) at the definitive primitive streak stage. It also produced changes in the shape and behaviour of PGCs since more than half of them adhered to one another, forming groups or chains of three or more cells and, in contrast to their characteristic spherical form, most single PGCs displayed a fibroblastic appearance. On the 2nd day of incubation most PGCs remained adherent to each other, which did not hinder them from entering the extra-embryonic blood vessels of the crescent. Ultrastructural analysis showed that PGCs adhered to each other by large areas of cell membrane apposition and specialized adhesive structures, such as tight junctions and desmosomes. PGCs also displayed many lamellipodial and filopodial processes. The effects of DA on PGCs were prevented by either glucose or EDTA. Although it is difficult to account for the effect of glucose, the effect of EDTA suggests that the action of DA may be calcium-dependent.