EXPRESSION OF LUTEINIZING-HORMONE HUMAN CHORIONIC-GONADOTROPIN (LH HCG) RECEPTOR MESSENGER-RNA IN THE HUMAN OVARY/

The gonadotrophins follicle stimulating hormone (FSH) and luteinizing hormone (LH) are key hormones in the regulation of ovarian function. I n the present study, the expression of LH/human chorionic gonadotrophi n (HCG) receptor mRNAs in the human ovary was examined. Northern blot analysis was used to measure relative amounts of LH/HCG receptor mRNA, and in-situ hybridization was used to localize LH/HCG receptor transc ripts. Northern blot analysis of human ovaries detected three transcri pts (5.4, 3.6 and 2.4 kb) for the LH/HCG receptor. LH/HCG receptor mRN A concentrations increased from preovulatory follicles to the corpus l uteum of the midluteal phase, and decreased at the late luteal phase. Using in-situ hybridization, LH/HCG receptor mRNA was located predomin antly in granulosa cells in the same follicle. Cloning of the human LH / HCG receptor cDNA previously revealed the existence of two alternati ve forms of the receptor differing by the presence (HLH-Ra) and absenc e (HLH-Rb) of 62 amino acids encoded by exon 9. We have studied the fu nctional significance of these receptor isoforms and have confirmed th at they are generated by alternative splicing. A reverse transcription -polymerase chairs reaction amplification was used to detect different isoforms of LH receptor mRNAs in ovary and placenta. The expression o f the two mRNA forms of LH/HCG receptor were detected in ovary, and at very low concentrations in placenta. Treatment with HCG caused a dose -dependent increase in cAMP production with an initial response eviden t at similar to 1 ng/ml HCG in COS-7 cells expressing HLH-Ra. However, a complete loss of signal transduction was found in cells transfected with the truncated HLH-Rb.