Mechanisms of Regulation in Follicular Growth

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Cloning of the human LH/HCG receptor cDNA previously revealed the existence of two alternative forms of the receptor differing by the presence (HLH-Ra) and absence (HLH-Rb) of 62 amino acids encoded by exon 9. We have studied functional significance of these receptor isoforms and have confirmed that they are generated by alternative splicing. A reverse transcription-polymerase chain reaction amplification was used to detect different isoforms of LH receptor mRNAs in ovary and placenta. The expression of the two mRNA forms of LH/HCG receptor were detected in ovary, and at very low concentrations in placenta. Treatment with HCG caused a dosedependent increase in cAMP production with an initial response evident at -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.