Molecular and Cell Biological Analysis of Lipid Kinases in Relation to Signaling and Vesicle Traffic.

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The cloning and characterization of a novel class II phosphoinositide (PI) 3-kinase was succeeded from the cDNA library of regenerating rat liver. This enzyme molecule composed of 1505 amino acids contained a C2 domain and displayed a restricted substrate specificity for PtdIns and PtdIns 4-P and, thus termed PI3K-IIgamma. This molecule was localized in the juxtanuclear Golgi region in the over-expressed in vitro cells. The mRNA expression was confined to the liver throughout the development and its expression increased during liver regeneration after partial hepatectomy.The gene expression for a subtype of phosphatidate (PA) phosphatase termed Dri42 was confined to the ventricular germinal zone of embryonic brain. PAP catalyses a dephosphorylation of PA to produce diacylglycerol (DG), an reverse process of phosphorylation by DG kinase whose molecular identification has been intensively performed by us. The localization of mRNAs for synaptojanin, inositol 5-phosphatase, in the brain was also revelaed by in situ hybridization histochemistry. Synaptojanin 1 mRNA was expressed in almost all neurons of the brain throughout developing and mature stages while synaptojanin 2 mRNA was first detected in neurons on early postnatal stages and the expression was evident in the white matters presumptive oligodendrocytes as the postnatal development proceeded. All these findings on dephosphorylation were instructive for understanding the significance of phosphorylation by lipid kinases.The gene expression localization of CDP-DG synthase and phosphatidylinositol synthase, both of which are involved in the two sequential PI-metabolic processes, was analyzed and some discrepant expression patterns were found spatio-temporally in developing and mature brain. The gene expression localization of phospholipase D in the brain is also under way by in situ hybridization histochemistry.