Abstract 309: A Female Myh11-CreER T2 Mouse Line Resulting from Y to X Chromosome-translation

Abstract

The Myh11-CreER T2 mouse line ( Cre +/ ) provides a powerful tool for studying the role of smooth muscle cells (SMCs) in the pathogenesis of vascular diseases. The Cre allele was initially inserted into Y chromosome, and thus excluded its inheritance by female mice. However, a number of vascular diseases exhibit sexual dimorphism in development and progression, and the underlying mechanisms may involve regulation of SMC biology by the dosage-effects of sex-linked genes and gender. A Cre line that induces SMC-specific gene deletion in female mice would complement the existing Cre +/ line to address this critical issue. Our lab established the Cre +/ colony with one male ancestor and it spontaneously separated to two subcolonies during subsequent breeding. One subcolony produced only male Cre +/ progenies, but the other produced both male and female Cre +/ progenies, indicating chromosome-translocation of the Cre allele. In view of this observation, we mapped the chromosome-location of the Cre allele for these subcolonies with cross-breeding experiments. The 1 st experiment crossed two Cre +/ males from the first subcolony with four Cre -/ females. Of the produced progenies, all males ( n =9) carried and all females ( n =22) did not carry the Cre allele, which favors Y chromosome- ( Y Cre+ ) over autosome-location of the Cre allele in this subcolony (Bayes Factor>1000). In the 2 nd experiment, a Cre +/ female from the second subcolony was bred with a Cre -/ male. Then, a Cre +/ male progeny of these breeders was mated with a Cre -/ female. The former breeding pair exhibited equal inheritance of the Cre allele by its male and female offspring. The latter breeding pair showed that all female progenies ( n =8) did, but all male progenies ( n =4) did not, carry the Cre allele. The data favors X chromosome- ( X Cre+ ) over autosome-location of the Cre allele in this subcolony (Bayes Factor>1000). To assess the recombination driven by Cre +/ allele with different chromosome-location, we crossed X Cre+ and Y Cre+ strains with R26R reporter mice. Robust Cre activity (x-gal staining) was observed in vascular SMCs of Y Cre+ and X Cre+ mice. The X Cre+ mice generated via Y to X chromosome-translocation thus represents a novel strain that is suitable for inducible gene deletion in SMCs of female mice.