A targeting vector was designed to replace exon 6 of the X-linked monoamine oxidase B (Maob) gene with a neomycin resistance (neo) cassette. The construct was electroporated into either 129S/SvEv-derived CCE embryonic stem (ES) cells or 129S4/SvJae-derived CCE ES cells. Correctly targeted ES cells were injected into C57BL/6 blastocysts and the resulting chimeric males were bred to 129/Sv females. The male offspring were backcrossed at least 25 generations to 129/Sv females resulting in Maob deficient mice (Stock No. 014133). A mutation, designated MaoaK284stop, arose spontaneously in exon 8 of the X-linked monoamine oxidase A (Maoa) gene of one male animal. This mutation was caused by a transversion at nucleotide 863, resulting in a premature stop codon at residue 284. This mutant male was backcrossed to a 129/Sv female, and the resulting female offspring were bred to 129/Sv males. Half of the resulting male offspring carried both mutations. Upon arrival at The Jackson Laboratory, mice were bred to 129S1/SvImJ (Stock No. 002448) for at least one generation to establish the colony.
A 32 SNP (single nucleotide polymorphism) panel analysis, with 27 markers covering all 19 chromosomes and the X chromosome, as well as 5 markers that distinguish between the C57BL/6J and C57BL/6N substrains, was performed on the rederived living colony at The Jackson Laboratory Repository. 4 of the 27 markers throughout the genome suggested a C57BL/6 genetic contribution from an unknown source.
