Variable Cre Recombination Efficiency in Placentas of Cyp19-Cre ROSA^mT/mG Transgenic Mice

Area of Science:

• Developmental Biology
• Genetics
• Reproductive Biology

Background:

• The aromatase-Cre (Cyp19-Cre) mouse model is widely used for placenta-specific gene inactivation.
• Unexpected phenotypes observed in pilot studies necessitated a thorough characterization of Cyp19-Cre placental function.

Purpose of the Study:

• To extensively characterize placental phenotypes in the Cyp19-Cre mouse model using ROSA^mT/mG reporter mice.
• To evaluate the reliability of placenta-specific gene inactivation mediated by Cyp19-Cre.

Main Methods:

• Bi-transgenic Cyp19-Cre;ROSA^mT/mG mice were generated by mating Cyp19-Cre and ROSA^mT/mG strains.
• Placental and fetal tissues were analyzed at embryonic day 17.5.
• Cre-mediated recombination was assessed via enhanced green fluorescent protein (EGFP) expression and tdTomato excision.

Main Results:

• Only ~50% of Cyp19-Cre;ROSA^mT/mG placentas exhibited Cre recombination activity.
• Variable recombination efficiency and mosaic EGFP expression patterns were observed within placentas.
• Maternal inheritance of the Cre allele resulted in significantly higher recombination activity.

Conclusions:

• The Cyp19-Cre model exhibits frequent mosaicism, inconsistent recombination, and parent-of-origin effects in placental gene inactivation.
• Tail-biopsy genotypes may not accurately predict gene excision in Cyp19-Cre positive placentas.
• Placenta-specific mutagenesis studies using Cyp19-Cre require careful characterization and interpretation of observed phenotypes.