Phospholipase C-eta2 is highly expressed in the habenula and retina

Phospholipase C (PLC), a key enzyme involved in phosphoinositide turnover, hydrolyzes phosphatidylinositol 4,5-bisphosphate to generate two second messengers, inositol 1,4,5-triphosphate and diacylglycerol. PLCeta2 (PLCη2), a neuron-specific isozyme of PLC, is abundantly expressed in the postnatal brain, suggesting the importance of PLCη2 in the formation and maintenance of the neuronal network in the postnatal brain. However, the detailed expression patterns of PLCη2 in the brain and other neuronal tissues remain to be clarified. Here, we generated PLCη2 knockout/LacZ knockin (plch2lacZ/lacZ) mice—the first mice to lack full-length PLCη2. Although the plch2lacZ/lacZ mice exhibited no obvious abnormalities, the LacZ reporter revealed unexpected and abundant expressions of PLCη2 in the habenula and retina. We confirmed these PLCη2 expression patterns by in situ hybridization and immunohistochemical analyses. In the retina, strong PLCη2 expression was detected in the photoreceptor (rod/cone), outer nuclear layer, outer plexiform layer, and inner nuclear layer, suggesting that PLCη2 is expressed in rods and cones, and also in horizontal, bipolar, and amacrine cells, but not in ganglion cells. Interestingly PLCη2 exhibited a dynamic expression pattern during postnatal retinal development, strongly suggesting that this isozyme might be involved in the development and maturation of the retina. Since both the habenula and retina are thought to play important roles in the regulation of circadian rhythms, our results suggest that PLCη2 may be involved in the function of habenula and retina.