A genomic DNA fragment carrying the first two coding exons of LRRK2 was isolated from the RPCI-22 (129S6/SvEvTac) Mouse BAC Library (BACPAC Resources Center). One copy of a LoxP site was inserted into intron 1 followed by an insertion of a FRT-flanked neomycin expression cassette and the second copy of LoxP site into intron 2 of LRRK2. The targeting vector was linearized and transfected into 129/SvJ ES cells, which were later subjected to G418 selection for 7 days. The G418 resistant ES clones were picked and screened by Southern blot analysis for the correctly targeted clones. Two positive ES clones were expanded and injected into blastocysts. The resulting male chimera mice were bred with wild-type C57BL/6J female mice to obtain LRRK2+/neo mice. LRRK2+/neo mice were then crossed with Cre transgenic mice (Lakso et al., 1996 (link)) to generate LRRK2+/- mice in which exon 2 was deleted by Cre-mediated DNA recombination, resulting in a premature stop codon in exon 3. The heterozygous LRRK2+/- mice were intercrossed to generate the homozygous LRRK2-/- mice.