Comparative phenotypic analysis of the two major splice isoforms of phosphatidylinositol phosphate kinase type I gamma in vivo

Localized production of polyphosphoinositides is critical for their signaling function. To examine the biological relevance of specific pools of phosphatidylinositol 4,5-bisphosphate we compared the consequences of genetically ablating all isoforms of phosphatidylinositol phosphate (PIP) kinase type Iγ (PIPKIγ), encoded by the gene Pip5k1c , versus ablation of a specific splice isoform, PIPKIγ\_i2, with respect to three reported PIPKIγ functions. Ablation of PIPKIγ\_i2 caused a neuron-specific endocytosis defect similar to that found in PIPKIγ−/− mice, while agonist-induced calcium signaling was reduced in PIPKIγ−/− cells, but was not affected in the absence of PIPKIγ_i2. A reported contribution of PIPKIγ to epithelial integrity was not evident in PIPKIγ−/− mice. Given that mice lacking PIPKIγ_i2 live a normal lifespan whereas PIPKIγ−/− mice die shortly after birth, we propose that PIPKIγ-mediated metabotropic calcium signaling may represent an essential function of PIPKIγ, whereas functions specific to the PIPKIγ_i2 splice isoform are not essential for survival.