IDENTIFICATION AND CLONING OF THE MEMBRANE-ASSOCIATED SERINE-PROTEASE, HEPSIN, FROM MOUSE PREIMPLANTATION EMBRYOS

Previous studies have suggested the existence of a membrane-associated serine protease expressed by mammalian preimplantation embryos, In th is study, we have identified hepsin, a type II transmembrane serine pr otease, in early mouse blastocysts. Mouse hepsin was highly homologous to the previously identified human and rat cDNAs. Two isoforms, diffe ring in their cytoplasmic domains, were detected. The tissue distribut ion of mouse hepsin was similar to that seen in humans, with prominent expression in liver and kidney. In mouse embryos, hepsin expression w as observed in the two-cell stage, reached a maximal level at the earl y blastocyst stage, and decreased subsequent to blastocyst hatching. E xpression of a soluble form of hepsin revealed its ability to autoacti vate in a concentration-dependent manner. Catalytically inactive solub le hepsin was unable to autoactivate. These results suggest that hepsi n may be the first serine protease expressed during mammalian developm ent, making its ability to autoactivate critical to its function.