Phosphoinositide-specific phospholipase C (PLC) plays a crucial role in the initiation of receptor mediated signal transduction through the generation of the two second messengers, inositol 1,4,5-triphosphate and diacylglycerol from phosphatidylinositol 4,5-bisphosphate. There are many mammalian PLC isozymes, including PLC beta1, PLC beta2, PLC beta3, PLC beta4, PLCgamma 1, PLCgamma 2, PLC delta1, PLC delta2 and PLCe. PLCdelta exists as four different isoforms. PLC delta1, a calcium signal amplifier, is activated by an atypical GTP-binding protein. In addition, PLC delta1 is an effector for GTP-binding protein transglutaminase II-mediated oxytocin receptor and alpha1B-adrenoreceptor signaling. Mouse PLC delta1 is highly expressed in brain, heart, lung and testis. PLC delta is abnormally accumulated in autopsied brains with Alzheimer