Homozygous Stra8-cre transgenic mice are viable and fertile, with expression of an optimized variant of Cre recombinase (iCre) directed by the 1.4 kb mouse Stra8 (stimulated by retinoic acid gene 8) genomic promoter fragment. Postnatal Cre-recombinase expression is first observed in testes at postnatal day (P)3 (early-stage spermatogonia), increases out to P7 (pre-leptotene-stage spermatocytes), and is not detected in other tissues examined (including ovaries). In addition, no cre expression is reported in male or female embryos. When Stra8-cre transgenic males are bred with female mice containing a loxP-flanked sequence, Cre-mediated recombination will result in deletion of the floxed sequence, specifically during these stages of spermatogenesis. The Donating Investigator has not attempted to make the congenic B6 strain homozygous. As Stra8-cre transgene expression is specific to developing sperm, transmission of the transgene must be through the male germline for experiments involving cre-induced recombination.
In an attempt to offer alleles on well-characterized or multiple genetic backgrounds, alleles are frequently moved to a genetic background different from that on which an allele was first characterized. This is the case for the strain above. It should be noted that the phenotype could vary from that originally described. We will modify the strain description if necessary as published results become available.
