This is a proposal to generate a conditional S45F and a T41A knock-in allele of Ctnnb1. These are the two most common Ctnnb1 mutations found in desmoid tumors. Ozgene will generate the conditional mutant alleles by flanking wt exons 3-6 and an inverted murine cDNA of exons 3-15 with the S45F mutation or the T41A and an IRES_eGFP with loxP and lox2272 sites via gene targeting in mouse ES cells. The IRES_eGFP cassette within the KI will also be floxed with Rox sites. Breeding to flp will remove the neo cassette. Cre-mediated recombination of the “floxed” regions will delete the wt exons and invert the KI cDNA_IRES_eGFP into the proper orientation for expression. Both Ctnnb1 with the S45F mutation and eGFP will be expressed. Further breeding to Cre will excise the IRES_eGFP. Ctnnb1 with the S45F mutation, but not eGFP, should be expressed. This approach avoids potentially dominant negative effects of the knock-in mutation.
LAY VERSION OF ABSTRACT- “A genetically targeted mouse model of desmoid tumors.”