A LARGE-SCALE GENE TRAP SCREEN FOR INSERTIONAL MUTATIONS IN DEVELOPMENTALLY-REGULATED GENES IN MICE

We have used a gene-trap vector and mouse embryonic stem (ES) cells to screen for insertional mutations in genes developmentally regulated a t 8.5 days of embryogenesis (dpc). From 38,730 cell lines with vector insertions, 393 clonal integrations had disrupted active transcription units, as assayed by P-galactosidase reporter gene expression. From t hese lines, 290 clones were recovered and injected into blastocysts to assay for reporter gene expression in 8.5-dpc chimeric mouse embryos. Of these, 279 clones provided a sufficient number of chimeric embryos for analysis. Thirty-six ( 13%) showed restricted patterns of reporte r-gene expression, 88 (32%) showed widespread expression and 155 (55%) failed to show detectable levels of expression. Further analysis show ed that approximately one-third of the clones that did not express det ectable levels of the reporter gene at 8.5 dpc displayed reporter gene activity at 12.5 dpc. Thus, a large proportion of the genes that are expressed in ES cells are either temporally or spatially regulated dur ing embryogenesis. These results indicate that gene-trap mutageneses i n embryonic stem cells provide an effective approach for isolating mut ations in a large number of developmentally regulated genes.