Generation of mice lacking either p90 PIP5KIγ alone or lacking both PIP5KIγ isoforms. (A) The PIP5KIγ E17 conditional targeting vector contains loxP sites flanking exon 17. These mice were crossed with PF4 or CMV promoter-driven Cre recombinase. (B) RT-PCR and immunoblotting confirmed that platelets from homozygous floxed PIP5KIγ E17^−/− PF4 Cre⁺ mice did not express detectable p90 PIP5KIγ mRNA or protein. Similar results were obtained using platelet mRNA or lysates derived from PIP5KIγ E17^−/− CMV Cre⁺ mice (not shown). (C) Conditional rescue of the PIP5KIγ gene trap. The diagram shows the location of the β-geo trap within the first intron of the PIP5KIγ gene. The insertion leads to a read-through mutation within the first intron of the targeted gene and truncated PIP5KIγ after the 32nd amino acid. The location of the LoxP sites flanking the splice acceptor is shown. (D) PIP5KIγ expression is seen in brain and in platelet lysates. The anti-PIP5KIγ immunoblot shows the complete loss of protein in all analyzed tissues derived from the PIP5KIγ^−/− MLC-2v Cre⁺ mice.