Clarifying Frizzled 2 function in development through genetically validated mouse models.

Wnt receptors of the Frizzled (Fzd) family are widely considered to exhibit substantial functional redundancy, complicating efforts to therapeutically target individual receptors. Fzd2 was believed to be functionally redundant with Fzd1 and Fzd7, based on previously published global knockout mouse studies. By contrast, homozygosity for a Fzd2 global knockout mouse allele developed by the International Mouse Phenotype Consortium (IMPC) has been reported to cause embryonic lethality, suggesting that Fzd2 is critical for early embryonic development. If global deletion of Fzd2 leads to early lethality, conditional deletion models are necessary to identify tissue-specific phenotypes. We found that a previously published Fzd2 conditional deletion model does not eliminate Fzd2. We have generated a new conditional model to address the contradictory previous studies and allow tissue-specific studies of Fzd2. We successfully inserted two loxP sites around the Fzd2 gene and confirmed that subsequent Cre-mediated recombination creates a Fzd2 null allele. Global deletion of Fzd2 in this model does not cause embryonic lethality while limb-specific deletion causes limb shortening. This work supports the hypothesis that Fzd2 regulates limb development and emphasizes the importance of thoroughly validating newly generated mouse models.