A. Mishra et Pb. Seshagiri, Evidence for the involvement of a species-specific embryonic protease in zona escape of hamster blastocysts, MOL HUM REP, 6(11), 2000, pp. 1005-1012
The source and nature of zona lytic factors during zona escape of hamster b
lastocyts were investigated. When cultured in hamster embryo culture medium
(HECM)-2h, all 8-cell embryos (n = 135) developed to zona escaped-blastocy
sts with complete zona lysis. In addition, 2-cell embryos, when co-cultured
with tons 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 c
ultured with zona-escaping blastocysts, However, zonae from mice, rats, she
ep and humans were resistant to lysis under these conditions. Pronase treat
ment 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 +/- 13 s). When cysteine protease i
nhibitors (antipain, leupeptin, E-64 and p-hydromercuricbenzoate) were test
ed, they completely inhibited zona escape, while trypsin inhibitors (TLCK a
nd SBTI) did not. Uterine zona lysin contribution in zona escape was discou
nted since: (i) uterine luminal flushing and endometrial extract from day 4
(the time of zona escape in vivo) pregnant females failed to lyse zonae an
d (ii) endogenous oocytes and transferred 2-cell embryos (to day 3 pseudopr
egnant recipients) were all zona-intact, while 71% of transferred blastocys
ts exhibited zona escape, following their recovery after 24 h. These observ
ations suggest that a species-specific, embryonic proteolytic factor, with
a cysteine protease-like activity, is involved in the zona escape of blasto
cysts in hamsters.