Generation of a novel Stra8-driven Cre recombinase strain for use in pre-meiotic germ cells in mice†

The development of oocytes occurs over a broad time frame, starting at the earliest stages of embryogenesis and continuing into adulthood. Conditional knockout technologies such as the Cre/loxP recombination system are useful for analyzing oocyte development at specific stages, but not every time frame has appropriate Cre drivers, for instance, during oocyte meiotic initiation through early prophase I in the embryo. Here, we generated a novel knockin mouse line that produces a bicistronic transcript from the endogenous Stra8 locus that includes a "self-cleaving" 2A peptide upstream of cre. This allows for high efficiency cleavage and production of both proteins individually and results in expression of cre in both male and female gonads at the biologically relevant stage. Fluorescent reporter analysis confirms that this line recapitulates endogenous Stra8 expression in both sexes and does not affect fertility of heterozygous nor homozygous mice. This line, named Stra8P2Acre, adds to the repertoire of germ-cell specific cre driver lines and, importantly, allows for deletion of target genes during key embryonic oocyte developmental stages, including early events in meiosis. Summary Sentence Generation of a novel cre recombinase knockin to the Stra8 locus allows production of Stra8 and cre without affecting fertility.