Glycoprotein hormone receptors contain a large extracellular domain that is encoded by multiple exons, facilitating the possibility of expressing alternatively spliced transcripts. We have cloned two new splice variants of the rat follicle-stimulating hormone (FSH) receptor gene: FSH-R1 and FSH-R2. The splice variant FSH-R1 differs from the full-length FSH receptor mRNA by the inclusion of a small extra exon between exons 9 and 10. FSH-R2 lacks the first three base pairs of exon 4, contains an extra exon between exons 4 and 5, and has an extended 3'-untranslated region. According to the predicted open reading frames, both mRNAs encode truncated FSH receptor proteins, consisting of the entire extracellular domain (FSH-R1) or the amino-terminal half of the extracellular domain (FSH-R2), and are expressed at a low level in testes and ovaries. The levels of expression of the FSH-R1 and FSH-R2 mRNAs in the gonads show a constant ratio to the expression level of the full-length FSH receptor mRNA. Furthermore, in vitro co-expression of either one of the truncated proteins with the full-length FSH receptor in COS1 cells did not affect signal transduction through the full-length FSH receptor. The absence of a function of the truncated FSH receptors in FSH signal transduction in vitro, and the lack of differential regulation of the alternative transcripts, indicate that there is no clear function for alternative splicing of the FSH receptor pre-mRNA in the postnatal testis and the cycling adult ovary.

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