Fzd1 Knockout mouse models

Fzd1, the mouse ortholog of human FZD1, encodes a seven transmembrane Frizzled receptor whose extracellular cysteine rich domain binds the palmitoleate-modified thumb of Wnt ligands, and whose intracellular KTXXXW motif recruits Dishevelled to nucleate the signalosome that, together with LRP5 or LRP6, inhibits the beta-catenin destruction complex. Receptor abundance is set post-translationally by the E3 ligases RNF43 and ZNRF3, which ubiquitinate the intracellular loops for internalization and are themselves antagonized by RSPO ligands acting through LGR4, LGR5 and LGR6, the axis exploited by porcupine and anti-FZD therapeutics. FZD1 participates in canonical signaling in kidney, lung and bone and contributes to injury responses in fibrosis. Null mice are essentially normal because ten Frizzled paralogs share ligands, with Fzd2 and Fzd7 being the closest functional relatives, so single deletion is nearly uninformative and compound conditional alleles are mandatory. Use humanized CRD knockins when the goal is testing Frizzled selective antibodies whose epitopes do not cross-react with mouse receptor.

Whole body loss of Fzd1 gives the clearest readout when the question is whether the gene is required at all. Follow up tissue work can still move to a conditional allele if lethality or compensation appears.