Expression of urokinase-type plasminogen activator in human preimplantation embryos

During embryo implantation in the human trophoblast cells invade the endometrium and plasminogen activators (PA) are implicated in this tissue invasion process. Our studies on surplus embryos from patients undergoing in-vitro fertilization (IVF) treatments showed that PA activity was present in secretions of blastocysts but not embryos at the 2-4-cell stage. The secretion of this PA activity by blastocysts was increased by the addition of epidermal growth factor (EGF) to the embryo cultures. This PA activity had a molecular weight similar to that of urokinase-type PA (uPA). The mRNA for uPA was present in blastocysts, as determined by the reverse-transcription and polymerase chain reaction (RT-PCR) technique. These data indicate that uPA is produced by human preimplantation embryos and may play a role in early human development and embryo implantation.