Actb^tm2Npa

A vector was constructed where a recombinase-mediated cassette exchange (RMCE) site was placed downstream of a floxed stop cassette. The RMCE site consisted of a mutant FRT site, a promoterless EGFP reporter gene, a neomycin selection cassette and a wt FRT site. The vector targeted exon 2 of the beta-actin gene and disrupted its expression. Heterozygous animals had no reporter gene expression as assessed by fluorescent microscopy of brain, heart, liver and other organs. Upon removal of the stop codon by Cre recombinase, strong EGFP expression was observed. ES cells containing this allele allow for 1) RMCE into the b-actin locus and 2) initiating expression of the exchanged cassette by Cre-mediated excision of the stop codon. (J:129105)