Biology of reproduction
Preimplantation embryos from a variety of mammalian species contrast markedly in their response to culture in vitro. Murine preimplantation embryos display a wider tolerance than other mammalian species to culture environments, and this has contributed to the development of several effective defined culture media. Embryo coculture on somatic cells remains the most effective method of supporting reasonable rates of bovine preimplantation development in vitro. The patterns of gene expression for several antioxidant enzymes during preimplantation murine and bovine development were examined by use of the reverse transcription-polymerase chain reaction technique to determine whether the differential developmental capacity of mammalian preimplantation embryos in culture may reflect variations in the patterns of expression for a series of antioxidant enzymes. Transcripts for catalase, CuZn-containing superoxide dismutase (CuZn-SOD), Mn-SOD, glutathione peroxidase (GPX), and glutamylcysteine synthetase (GCS) were detected in mouse embryos at all stages of development regardless of in vivo or in vitro development. Preimplantation cow embryos produced by in vitro procedures expressed mRNAs for catalase, CuZn-SOD and GPX, whereas transcripts for Mn-SOD were not detected at any stage. GCS transcripts, although present in stages up to the morula, were not detected in cow blastocysts. Analysis of antioxidant gene expression in both bovine primary oviductal cell monolayer cultures and nonattached, ciliated oviductal cell vesicle cultures revealed a constitutive pattern of expression of all five enzymes for the 8-day culture interval. These experiments suggest that differences in gene expression may contribute to the variation in the ability of embryos to develop in vitro with respect to levels of oxygen and dependence on coculture.