Promiscuous recombination of LoxP alleles during gametogenesis in cornea Cre driver mice

Purpose: To examine whether promiscuous Cre/LoxP recombination happens during gametogenesis in double transgenic mice carrying LoxP modified alleles and Cre transgene driven by tissue-specific promoter outside the gonads of adult mice. Methods: Cre driver mice were crossbred with reporter mouse lines (e.g., ZEG and Rosa26R) to obtain Cre/ZEG and Cre/Rosa26R double transgenic mice. The frequency of promiscuous LoxP/Cre recombination was determined by the expression of second reporter genes in the offspring of double transgenic mice. Results: The frequency of promiscuous LoxP/Cre recombination varied in different lines of Cre driver mice and in the sex of the same driver mice with higher penetrance in male than in female double transgenic mice. Polymerase chain reaction (PCR) and recombination analysis demonstrate that the recombination of floxed allele occurs during the transition from spermatogonia (diploid) to primary spermatocyte (tetraploid) in the testis. Thereby, target-floxed allele(s) may be ubiquitously ablated in experimental animals intended for tissue-specific gene deletion. Conclusions: Gametogenesis-associated recombination should always be examined in tissue-specific gene ablation studies.