Zona pellucida glycoprotein mZP3 produced in milk of transgenic mice is active as a sperm receptor, but can be lethal to newborns

Mouse egg zona pellucida glycoprotein mZP3 (similar to 83 kDa M-r) serves a s a species-specific sperm receptor and acrosome reaction-inducer during fe rtilization in mice. These biological activities are dependent on certain m ZP3 serine/threonine- (O-) linked oligosaccharides present at the combining -site for sperm. In an attempt to produce large amounts of biologically act ive mZP3, we generated several transgenic mouse lines carrying the full-len gth mZP3 gene fused to the beta-casein gene promoter and transcription term ination sequence. We found that different transgenic mouse lines have diffe rent amounts of recombinant mZP3 (similar to 63 kDa M-r) in milk of lactati ng females, from similar to 0.3 to 3.5 mu g/mu l of milk. In all cases, pur ified milk-mZP3 is active as a sperm receptor and acrosome reaction-inducer in vitro. Unexpectedly, we also found that development of litters from the se transgenic mice is related to the amount of mZP3 in the mother's milk. I n the most extreme case, litters from the highest expressers fail to live b eyond about day-7 post partum unless placed immediately after birth with su rrogate wild-type mothers. Litters from lower expressers initially display a complex phenotype that includes effects on hair and body growth, but some of the mice survive and, in time, are restored to a wild-type phenotype. T hese results demonstrate that relatively large amounts of biologically acti ve mZP3 can be produced in transgenic mouse milk for structural and other s tudies, but that the presence of mZP3 in milk has dramatic developmental ef fects on litters, ranging from retarded hair and body growth to death of ne wborn pups.