A cre/ERT2 expression sequence was inserted downstream of the Mchr1 promoter on the RP23-202N16 BAC via homologous recombination/BAC recombineering; this replaced nucleotides 4-41 from exon 1 and was designed to disable transcription/translation of the Mchr1 protein from the BAC Mchr1 locus. An frt-flanked kanamycin selection cassette used during homologous recombination/BAC recombineering was removed by transient FLP plasmid injection. The resulting Mchr1-cre/ERT2 BAC transgene was purified for subsequent male pronuclear injection to establish transgenic founder animals. Two lines 2 and 3 were generated with similar expression patterns.
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