Plasminogen activator in mouse and rat oocytes: induction during meiotic maturation

We have found that ovulated mouse and rat oocytes contain tissue-type plasminogen activator (PA). Primary oocytes isolated from ovaries did not contain the enzyme. During spontaneous meiotic maturation in vitro, tissue-type PA became detectable 5 hr after germinal vesicle breakdown. Induction of tissue-type PA activity was blocked by dibutyryl-cAMP or isobutylmethyl-xanthine as well as by cycloheximide, but not by actinomycin D or alpha-amanitin. These results suggest that tissue-type PA mRNA is present in primary oocytes, and that translation of this mRNA is triggered upon resumption of meiotic maturation. Tissue-type PA catalyzed proteolysis around live secondary oocytes and fertilized eggs, indicating secretion of the enzyme. Unlike secondary oocytes, fertilized eggs denuded of their zona pellucida no longer contained the enzyme, suggesting that tissue-type PA production stops at or around fertilization, and that the bulk of the enzyme is secreted at this time.