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Molecular Human Reproduction, Vol. 6, No. 11, 1005-1012, November 2000
© 2000 European Society of Human Reproduction and Embryology

Embryo development

Evidence for the involvement of a species-specific embryonic protease in zona escape of hamster blastocysts

Archana Mishra and P.B. Seshagiri1

Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore-560012, India

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.

blastocyst/hamster/hatching/protease/zona escape

Notes

1 To whom correspondence should be addressed at: Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore 560 012, India. E-mail: polani{at}serc.iisc.ernet.in


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