To recapitulate a mutation in the orthologous human gene that disrupts the inhibitory wedge, a glutamate to arginine substitution at codon 613 (E613R) was engineered in exon 18 and incorporated at the endogenous locus via homolgous recombination. A single loxP site remained in intron 18 after the floxed neo cassette was excised. (J:66501)