Localization of receptors for luteinizing hormone/chorionic gonadotropin in neural retina.

Although the expression of the luteinizing hormone (LH)/human chorionic gonadotropin (CG) receptor gene has been traditionally thought to be restricted to gonadal tissue, recent studies have shown that LH/CG receptors are present in many regions of the central nervous system (CNS), as well as in peripheral tissues. We now report the characterization of LH/CG receptor gene expression in the neural retina, a component of the CNS. Transcript levels in the retina are approximately equal to levels present in the cerebral cortex, but are at least 100 fold lower than the levels in testis. The density of LH/CG receptor transcripts, receptor protein and 125I-CG binding is the highest in the photoreceptor cells and then decreased throughout the inner retina. Our study is the first to demonstrate the presence of LH/CG receptors in the neural retina. This finding raises the possibility that photoreceptor cells have the potential to mount cellular responses to LH/CG that may impact on visual processing, and poses an intriguing connection to the proposed role of gonadotropins in the progression of proliferative retinopathy.

Characterization of the human type 2 neuropeptide Y receptor gene (NPY2R) and localization to the chromosome 4q region containing the type 1 neuropeptide Y receptor gene.

Neuropeptide Y (NPY) signals through a family of G-protein-coupled receptors present in the brain and sympathetic neurons. To further our understanding of the genetic elements involved in the regulation of NPY receptor expression, we have cloned and characterized the human gene encoding the type 2 NPY receptor (Y2 receptor, HGMW-approved symbol NPY2R).2 The transcript spans 9 kb of genomic sequence and is encoded on two exons. As in the type 1 NPY receptor (Y1 receptor) gene, the 5'-untranslated region of the Y2 receptor is interrupted by an intervening sequence ( approximately 4.5 kb). However, the Y2 receptor gene does not contain an intron analogous to that present in the coding region of the Y1 receptor. The predicted transcript size ( approximately 4.5 kb) is consistent with the size observed by Northern analysis. The 381-amino-acid sequence deduced from the open reading frame is identical to that encoded by the cDNA. The Y2 receptor gene maps to human chromosome 4q31, the same region containing the Y1 receptor locus, suggesting that these subtypes may have arisen by gene duplication despite their structural differences.

The light-activated GTP-dependent cyclic GMP phosphodiesterase complex of bovine retinal rod outer segments. Dark resolution of the catalytic and regulatory proteins.

A cyclic GMP phosphodiesterase associated with retinal rod outer segment (ROS) membranes is fully activated only in the presence of light and GTP. Activity can be easily depleted from the membranes by hypotonic washing, which in darkness removes two major soluble proteins. One of these has cGMP phosphodiesterase activity which is no longer activated by light or GTP. The other lacks phosphodiesterase activity but copurifies with the catalytic protein unless special measures are taken. In the present report, these 2 proteins removed from the ROS in darkness were resolved in a manner which was qualitatively and quantitatively dependent upon concentrations of 2-mercaptoethanol and EDTA. We designated the catalytic protein as P and the other protein G, because it has been reported to exhibit GTP-related activities. The unresolved P and G proteins behaved as a single complex on native gels, analytical ultracentrifugation, sucrose gradient sedimentation, and gel filtration. The P:G complex had the same Mr as purified P and more stable phosphodiesterase activity. Removal of G from P destabilized the catalytic activity and allowed aggregation of P. With loss of activity by purified P, multiple slow migrating protein bands appeared upon native gel electrophoresis. Destabilization of P could be partially prevented by addition of Mg2+ before physical separation of P from G. If 2-mercaptoethanol was removed simultaneously, dissociation of the P:G complex and destabilization of P were prevented. These findings imply that the G protein is essential to the catalytic stability of P when both are removed in darkness from the ROS membrane.