Studies on the temporal correlation between secretion of plasminogen activator and stages of early mouse...

Fibrinolytic activity is associated with mouse embryos during preimplantation stages, but thorough analyses indicate that activity is restricted to the zona pellucida and is not likely to be of embryonic origin. Investigations on embryos developing further both in utero and in vitro suggest that plasminogen activator is unlikely to be involved in either hatching from the zona pellucida or the acquisition of adhesiveness by trophoblast cells. However, the enzyme is invariably secreted by blastocysts that have reached the stage of trophoblast invasiveness; fibrinolytic activity is even produced by most embryos which have failed to hatch from their zona but remain viable at the time of acquisition of invasive properties by trophoblast cells from other, normally developing, embryos. These studies are, therefore, consistent with the view that plasminogen activator is involved in trophoblast invasiveness. Possible functions of the enzyme during migration of trophoblast cells through tissue layers are considered.