MATERNALLY EXPRESSED PGK-CRE TRANSGENE AS A TOOL FOR EARLY AND UNIFORM ACTIVATION OF THE CRE SITE-SPECIFIC RECOMBINASE

A transgenic mouse strain with early and uniform expression of the Cre site-specific recombinase is described. In this strain, PGK-Cre(m), C re is driven by the early acting PGK-1 promoter, but, probably due to cis effects at the integration site, the recombinase is under dominant maternal control. When Cre is transmitted by PGK-Cre(m) females mated to males that carry a reporter transgene flanked by loxP sites, even offspring that do not inherit PGK-Cre delete the target gene. It follo ws that in the PGK-Cre(m) female Cre activity commences in the diploid phase of oogenesis. In PGK-Cre(m) crosses complete recombination was observed in all organs, including testis and ovary. We prepared a mous e stock that is homozygous for PGK-Cre(m) and at the albino (c) locus. This strain will be useful for the early and uniform induction of ect opic and dominant negative mutations, for the in vivo removal of selec tive elements from targeted mutations and in connection with the manip ulation of targeted loci in `knock in' and related technologies.