The targeting vector consists from 5' to 3': a loxP site followed by the 3'-end (1.4-kb) of mouse intron 1; the murine exon 2 replaced by the human P2RX7 cDNA comprising exons 2-13; a reverse oriented selection marker flanked by frt sites which consists of a phosphoglycerate kinase (PGK) promoter driven neomycin resistance gene equipped with a bovine growth hormone (bGH) poly A signal (pA), a second loxP site and a quadruple poly A signal consisting of a bGHpA, a PGK pA, and 2 SV40 pAs. After germ-line transmission of the modified allele via homologous recombination in ES cells, offspring from male chimeras are bred. The FRT flanked neo cassette was removed by breeding to deleter-flp mice.