Variable Cre Recombination Efficiency in Placentas of Cyp19-Cre ROSAmT/mG Transgenic Mice

The aromatase-Cre recombinase (Cyp19-Cre) transgenic mouse model has been extensively used for placenta-specific gene inactivation. In a pilot study, we observed unexpected phenotypes using this strain, which prompted an extensive characterization of Cyp19-Cre placental ROSAmT/mG reporter mice. two strains were mated to generate bi-transgenic Cyp19-Cre;ROSAmT/mG mice following standard breeding scheme, and fetal tissues analyzed on embryonic day 17.5. Both maternal paternal Cre inheritance by mating the respective males females. genotype results showed expected percentage fetuses (73%) mRNA was expressed in all placentas. However, surprisingly, only about 50% placentas Cre-mediated activity as demonstrated enhanced green fluorescent protein (EGFP) expression. Further genetic excision analysis revealed consistent showing absence tdTomato lacking EGFP Moreover, among EGFP-expressing placentas, there wide variability recombination efficiency, even from same litter, leading mosaic pattern expression different zones cell types addition, significantly higher with inheritance. Our show frequent mosaicism, inconsistent activity, parent-of-origin effects mice, suggesting that tail-biopsy may not necessarily indicate floxed genes positive Thus, mutagenesis studies require careful interpretation each allele.