The E1A transcriptional control region is efficiently activated in proliferating tissues of transgenic mice

To study the in vivo regulation of the adenovirus E1A transcriptional regulatory region in transgenic mice, we have constructed two hybrid genes in which the viral control element regulates the expression of the CAT and the lacZ reporter gene. The fusion constructs were introduced into the mouse germline. The expression of the transgenes were monitored during embryogenesis and during postnatal development as well as in adult organs. We show that the E1A regulatory region is recognized and activated in undifferentiated cells during early embryonic cleavage, in the morula, in the inner cell mass and in the trophectoderm of the blastocyst. Transcription initiation at the E1A promoter leads to higher marker gene expression in proliferative centers in postimplantation embryos at the beginning of the neural tube closure. Analysing marker gene expression during postnatal development, a correlation of transcriptional activity of the E1A regulatory region and cell proliferation could be demonstrated. The expression profile of the transgene in different adult organs parallels with DNA synthesis. Marker gene expression was high in cells of organs known to have a high mitotic rate, such as the intestine, the stomach, the skin and the bone marrow, whereas little activity of the E1A control region was observed in the post-proliferative brain. These results are consistent with the finding that activation of the viral cis-regulating elements dramatically increased in the kidney after mitotic stimulation by folic acid. These observations strongly suggests a cell cycle regulated expression from the E1A enhancer/promoter in the absence of the E1A autoregulatory proteins in the living animal.