Biochemical Effect of An Inactivating Mutation of the Luteinizing Hormone Receptor Leung, Bear, Wu, Rennert, Chan in collaboration with Steinbach, Fechner. Luteinizing hormone/Chorionic gonadotropin Receptor (LHR) plays a key role in the development of the gonad and in reproductive physiology. In the testis, LHR activation leads to the production of testosterone. Inactivation of the LHR results in reduced production of testosterone and causes hypergonadotrophic hypogonadism in Leydig Cell Hypoplasia (LCH), a form of male pseudohermaphroditism. A novel missense mutation A340T identified in a patient with LCH resulted in substitution of Ile-114 by Phe, which affects one of the Leucine-rich repeats (LRR) in the extracellular domain of the hLHR. The mutant receptor failed to trigger cAMP production upon hCG stimulation in transient expression studies. This mutation did not affect trafficking of the receptor as revealed by fluorescent microscopic study of the green fluorescent protein of this receptor. It affected binding of the hormone by the receptor. A computer model of the LRR was generated to study the effect of this mutation. The model clearly demonstrated the conformational effect of the mutation. This finding may be extended to explain the impact of mutations on the biological activity of other proteins with LRRs. Novel Function of Luteinizing hormone/Chorionic Gonadotropin Receptor (LHR) in the Nervous System Meng, Rennert, Chan Individuals with LHR carrying activating mutations develop familial male-limited precocious puberty (FMPP) and are often shown to have behavioral problems. The cause is unclear. The behavioral problem of FMPP patients may be related to the dysfunction of brain cells caused by the expression of the mutated LHR. Recently LHR was shown to express in several non-gonad tissues including the nervous system. LHR expression level in the brain is developmentally regulated. In the adult rat LHR expression was detected in some neurons of specific brain regions, the ependymal cells of all four ventricles and the choroid plexus. The function of LHR in these cells is unknown. The goal of this study is to investigate the functional activity of LHR in the brain. The rat neuronal cell line, PC12 was transfected with an expression construct with the human LHR cDNA (hLHR) carrying an activating mutation, Asp578His (H mutation), inserted into pIRES2EGFP under the control of CMV promoter. Transfection with the mutated hLHR led to an initiation of neurite outgrowth in 10.8 +/- 1.8 % of cells which was significantly higher than that observed in cells transfected with the vector alone (3.9 +/- 0.8%) or transfected with the wild type hLHR (3.4 +/- 0.7%). Among the neurite-bearing cells, those transfected with the mutated LHR had a significantly higher proportion of cells that had neurites longer than 2x cell body (41.7%) as compared to those transfected with vector (15.5%) or wild type hLHR (19.2%). These results suggested the possible neurotrophic effects of hLHR in the brain. Further experiments are underway to elucidate the mechanism of LHR induced neuronal differentiation.