IMPROVEMENT OF GERM-LINE TRANSMISSION BY TARGETING BETA-GALACTOSIDASETO NUCLEI IN TRANSGENIC MICE

The Escherichia coli lacZ gene has frequently been used as a reporter in cell lineage analysis, in determining the elements regulating spati al and temporal gene expression, and in enhancer/gene trap detection o f developmentally regulated genes. However, it is uncertain whether la cZ expression affects eukaryotic cell growth and development. By using a gene trap, we previously isolated the promoter, Ayu1, which is acti ve in ES cells and in several tissues including the gonads. We used th is promoter and the nuclear location signal of the SV40 large T gene t o locate beta-galactosidase either in the cytoplasm or the nucleus. Tr ansgenic lines containing beta-galactosidase in the cytoplasm of a wid e variety of cell types did not transmit the transgene to their offspr ing. In contrast, transgenic mice, containing beta-galactosidase in th e nucleus, did transmit the transgene successfully. Interestingly, lac Z expression in the brain was more restricted when beta-galactosidase activity was detected in the cytoplasm. These data suggested that cyto ptasmic beta-galactosidase affects certain developmental processes or gametogenesis resulting in transmission distortion of the transgene, a nd that this effect can be reduced by targeting beta-galactosidase to the nucleus. We also found that Ayu1-driven lacZ expression in the duo denum of adult transgenic mice was sexually dimorphic, being positive in females and negative in males.