Self-sterility of eggs induced by exogenous and endogenous protease in the solitary ascidian,Halocynthia roretzi

The unfertilized eggs (UFE) of the solitary ascidian, Halocynthia roretzi, which are released naturally, are strictly self-sterile. However, ovarian eggs isolated after spawning, which are expected to develop into UFE on the following day, are self-fertile. Some exogenous proteases-trypsin, chymotrypsin, papain and elastase-induced self-sterility in the self-fertile ovarian eggs within an hour in vitro. The establishment of self-sterility by the exogenous protease did not require the synthesis of new protein, or the participation of follicle cells. Some of the ovarian eggs were able to differentiate into self-sterile eggs spontaneously in vitro. The protein synthesis inhibitors puromycin and cycloheximide had no effect on the spontaneous establishment of self-sterility. However, several protease inhibitors such as leupeptin, soybean trypsin inhibitor (SBTI) and antipain, did inhibit the spontaneous establishment of self-sterility. The possible participation of trypsin-like protease in the establishment of self-sterility in the ovary is discussed. Mol. Reprod. Dev. 52:99–106, 1999.