title: Evidence for the involvement of a species-specific embryonic protease in zona escape of hamster blastocysts.
abstract: The source and nature of zona lytic factors during zona escape of hamster blastocyts were investigated. When cultured in hamster embryo culture medium (HECM)-2h, all 8-cell embryos (n = 135) developed to zona escaped-blastocysts with complete zona lysis. In addition, 2-cell embryos, when co-cultured with zona escaping-blastocysts (at a ratio of 1:10), exhibited zona lysis. Various other embryos at the 1-8-cell stages also showed zona lysis when cultured with zona-escaping blastocysts. However, zonae from mice, rats, sheep and humans were resistant to lysis under these conditions. Pronase treatment resulted in rapid zona lysis in hamsters (7 +/- 1 s), whereas in other species zona lysis was much slower: mouse (662 +/- 27 s), rat (532 +/- 16 s), sheep (120 +/- 12 s) and human (104 +/- 8 s). When cysteine protease inhibitors (antipain, leupeptin, E-64 and p-hydromercuricbenzoate) were tested, they completely inhibited zona escape, while trypsin inhibitors (TLCK and SBTI) did not. Uterine zona lysin contribution in zona escape was discounted since: (i) uterine luminal flushing and endometrial extract from day 4 (the time of zona escape in vivo) pregnant females failed to lyse zonae and (ii) endogenous oocytes and transferred 2-cell embryos (to day 3 pseudopregnant recipients) were all zona-intact, while 71% of transferred blastocysts exhibited zona escape, following their recovery after 24 h. These observations suggest that a species-specific, embryonic proteolytic factor, with a cysteine protease-like activity, is involved in the zona escape of blastocysts in hamsters.
authors.affiliation: Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore-560012, India.
authors.forename: A
authors.initials: A
authors.lastname: Mishra
authors.forename: P B
authors.initials: PB
authors.lastname: Seshagiri
mesh_terms: D000818:Animals; D001755:Blastocyst / Q000166:cytology / Q000187:drug effects; D002374:Catalase / Q000494:pharmacology; D018920:Coculture Techniques / Q000379:methods; D006224:Cricetinae; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D010450:Endopeptidases / Q000378:metabolism*; D005260:Female; D006801:Humans; D008647:Mesocricetus; D051379:Mice; D009088:Mucoproteins / Q000378:metabolism; D009865:Oocytes / Q000378:metabolism; D011247:Pregnancy; D051381:Rats; D017208:Rats, Wistar; D012756:Sheep; D013045:Species Specificity; D013482:Superoxide Dismutase / Q000494:pharmacology; D014361:Trypsin Inhibitors / Q000494:pharmacology; D014599:Uterus / Q000378:metabolism; D015044:Zona Pellucida / Q000187:drug effects / Q000201:enzymology*
chemical_list: D015853:Cysteine Proteinase Inhibitors; D009088:Mucoproteins; D014361:Trypsin Inhibitors; C010393:lysin, gastropoda; D002374:Catalase; D013482:Superoxide Dismutase; D010450:Endopeptidases