These Ror2f/f mutant mice possess loxP sites flanking exons 3-4 of the receptor tyrosine kinase-like orphan receptor 2 (Ror2) gene. Mice that are homozygous for this allele are viable, fertile, normal in size and do not display any gross physical or behavioral abnormalities. ROR2 is a cell surface tyrosine-protein kinase receptor expressed during development of the facial primordia, limb mesenchyme, neural crest-derived tissues, and the genital tubercle. ROR2 is involved in cartilage and bone formation, and growth plate development, and is required for Wnt5a-mediated signaling. When bred to mice that express tissue-specific Cre recombinase, resulting offspring will have exons 3-4 deleted in the cre-expressing tissues. For example, when bred to Tg(EIIa-cre)C5379Lmgd transgenic mice, ROR2 null mice exhibit facial malformations, and truncation of the limbs and posterior region of the embryo. ROR2 null mice die soon after birth. This phenotype is more severe when Ror1 gene expression is also abolished (see Stock No. 018353). These double KO mice die by E14.5. The Jackson Laboratory 2024, used with permission.