Generalized tetracycline induced Cre recombinase expression through the ROSA26 locus of recombinant mice

Inducible Cre recombinase systems have been developed to bypass initial lethal phenotypes and to provide access to later embryonic or adult phenotypes. Here we describe the generation of a recombinant mouse that combines a tetracycline dependent switch with generalized Cre recombinase expression by targeting the ubiquitously expressed ROSA26 locus. This transgenic strain was developed using a simplified gene delivery system integrating both elements, the reverse tetracycline controlled trans-activator (rtTA) and rtTA inducible promoter into a single vector. In this transgenic strain, the endogenous ROSA26 promoter drives rtTA expression through a splice acceptor site. The tetracycline inducible promoter, cloned in opposite orientation to the ROSA26 locus and separated from the rtTA element by a 5 kb human p53 intron, drives Cre recombinase expression. Crossing these mice with a Cre reporter strain showed that Cre DNA-mediated recombination was ubiquitously and effectively induced during various prenatal developmental windows. Background Cre recombinase expression levels were observed in some tissues in the absence of the inducer, mostly during late embryonic developmental stages and in adult animals. Background recombination levels were low during development and most prominent in nervous tissue. Cre recombinase expression could not be effectively induced in adult animals. While rtTA mRNA levels were high in developmental and adult tissues, Cre recombinase mRNA levels remained low after doxycycline treatment. The mouse strain described here provides a valuable tool to further analyze the function of genes during specific developmental windows, by allowing the effective inactivation of their function throughout defined stages of embryonic development.