Esr1^tm1Mul

A loxP site was inserted into intron 8 and a neomycin resistance gene cassette, a second loxP site and a modified exon 9 were inserted downstream of the gene. The modification entails the change of tyrosine codon 541 (TAT) to serine (TCC) (p.Y541S). This mutation, in the ligand-binding domain (LBD) of the encoded receptor, leads to its constitutive activation and is the equivalent of the human p.Y537S mutation found in endocrine-resistant metastatic tumors. This allele expresses the wildtype transcript. Only after Cre-mediated deletion of the endogenous exon 9 and neo cassette, will the allele express the mutated transcript. (J:303707)