reproductive system
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• ovarian histology of mice expressing human ZP2 and ZP3 in place of the native mouse proteins appears normal
• zonae pellucidae of oocytes from mice expressing human ZP2 and ZP3 in place of their mouse orthologs appear similar histologically to those of wild-type mice; human ZP2 and ZP3 proteins are immunohistologically detectable, with mouse ZP1, throughout the zona matrix
• cumulus-free ovulated oocytes expressing human instead of mouse ZP2 and ZP3 bind mouse sperm, but fail to bind human sperm
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• female mice expressing human in place of mouse ZP2 and ZP3 ovulate approximately half the number of oocytes as do wild-type females when primed with pregnant mare serum and stimulated with human chorionic gonadotrophin
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• although human ZP2/ZP3 transgenes rescue the sterility of female mice lacking mouse ZP2 and ZP3, their average litter size is smaller than that of wild-type or ZP2 rescue mice
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embryo
• one- and two-cell embryos having human in place of mouse ZP2 and ZP3 exhibit persistent sperm binding, even after multiple washes using a wide-bore pipet
• cleavage of mouse ZP2 following fertilization is demonstrated by increased SDS-PAGE mobility of the reduced protein in the wild-type two-cell embryo versus in the ovulated oocyte; this mobility shift fails to occur in two-cell embryos in which human ZP2 and ZP3 replace their mouse orthologs
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• 24 hours after in vitro insemination, only 41% of ovulated oocytes in cumulus mass from female mice expressing human in place of mouse ZP2 and ZP3 had progressed to the 2-cell stage, versus 82% of wild-type and 68% of ZP2 rescue eggs
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