Expression of plasminogen activator genes and enzymatic activities in rat preimplantation embryos

Plasminogen activator has been implicated in tissue invasion and remodelling because of its role in the degradation of the extracellular matrix. Its activity can be detected in mouse embryos as early as day 6 of pregnancy, suggesting that plasminogen activator is involved in the process of implantation. The present study determined the time course of expression of the genes encoding tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA) during the preimplantation period in rats by the sensitive mRNA phenotyping procedure of reverse transcription-PCR. The tPA mRNA was present in rat oocytes and two-cell embryos, but was not detected between the four-cell and blastocyst stages. The uPA mRNA was first detected in two-cell rat embryos, and was present through to the blastocyst stage. In chromogenic assays, plasminogen activator activity was detected in oocytes and embryos between two-cell and blastocyst stages. Most plasminogen activator activity present in preimplantation embryos appeared to be uPA, as it could be inhibited by anti-uPA antibody and a specific uPA inhibitor, amiloride, but not by anti-tPA antibody. The present data demonstrate the expression of uPA gene and uPA activity in preimplantation rat embryos, suggesting that embryonic uPA may be involved in early embryo development and implantation.