Role of endogenous reverse transcriptase in murine early embryo development.

We report that a reverse transcriptase (RT) activity is present in early cleavage stage embryos as determined by a Polymerase chain reaction (PCR)-based detection assay. In an attempt to establish whether this activity plays a role in early embryonic development, we have blocked the endogenous RT by two independent approaches: (1) embryos were exposed to nevirapine, a highly specific nonnucleoside inhibitor of RT activity; (2) anti-RT antibody was microinjected into the nucleus of one blastomere of 2-cell embryos. When embryos were exposed to nevirapine in the developmental window between late 1-cell and 4-cell stages, development was arrested before the blastocyst stage. In contrast, development was not affected when embryos were exposed to nevirapine after the eight-cell stage. Developmental arrest was also induced when anti-RT antibody was microinjected in one blastomere of 2-cell embryos. Analysis of gene expression by RT-PCR in nevirapine-arrested 2-cell embryos revealed an extensive and specific reprogramming of gene expression, involving both developmentally regulated and constitutively expressed genes, compared to control embryos. These results support the conclusion that an endogenous RT activity is required in mouse early embryogenesis specifically between the late 1-cell and the 4-cell stage.