Treatment ofXenopus laevis coelomic eggs with trypsin mimics pars recta oviductal transit by selectively hydrolyzing envelope glycoprotein gp43, increasing sperm binding to the envelope, and rendering eggs fertilizable
✍ Scribed by Lindsay, Leann L.; Hedrick, Jerry L.
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 346 KB
- Volume
- 281
- Category
- Article
- ISSN
- 0022-104X
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✦ Synopsis
Xenopus laevis coelomic (body cavity) eggs are not fertilizable until they pass through the pars recta oviduct. A secreted pars recta oviductal protease with trypsin-like activity, oviductin, selectively hydrolyzes egg envelope glycoprotein gp43 to gp41; this limited proteolysis is believed to render the egg fertilizable. The effects of trypsin as a substitute for oviductin in modifying envelope structure and function were examined. Trypsinolysis (5 mIU for 30 min at room temperature) selectively converted gp43 to gp41 without hydrolysis of other envelope glycoproteins, and rendered coelomic eggs fertilizable in the presence of a jelly water preparation. Chymotrypsin had no effect on the acquisition of fertilizability, indicating that the reaction was dependent on trypsin-like specificity. This was confirmed by the use of p-aminobenzamindine and leupeptin to inhibit the ability of trypsin preparations to induce fertilizability. A sperm binding assay revealed that trypsin treatment dramatically increased sperm binding to egg envelopes derived from both coelomic eggs and ovarian eggs. Jelly water was not required for sperm binding. Therefore, trypsin can mimic the biological action of oviductin, selectively cleaving egg envelope gp43 to generate or expose sperm binding sites, rendering the envelope penetrable by sperm and permitting fertilization.