AN ALTERNATIVE GONADOTROPIN-RELEASING-HORMONE (GNRH) RNA SPLICING PRODUCT FOUND IN CULTURED GNRH NEURONS AND MOUSE HYPOTHALAMUS

Gonadotropin-releasing hormone (GnRH) is encoded by the proGnRH gene w hich contains four exons and three introns, In this study, two immorta lized GnRH-expressing cell lines (Gn11 and NLT) were characterized, Th e NLT and Gn11 cells, derived from a same brain tumor in a transgenic mouse, display neuronal morphology and neuron-specific markers, Howeve r, NLT cells secrete much higher levels of GnRH than Gn11 cells, To de lineate the mechanism underlying this difference, reverse transcriptas e-polymerase chain reaction and RNase protection assays were performed to examine proGnRH gene expression. While the mature proGnRH mRNA was predominately expressed in NLT cells, Gn11 cells express an abundant short transcript, Sequence analysis revealed that this short transcrip t contains exons 1, 3, and 4, but not exon 2, which encodes the GnRH d ecapeptide, RNase protection assays demonstrated that NLT cells expres s much higher levels of mature proGnRH mRNA than Gn11 cells, The lower level of GnRH secreting capacity in Gn11 cells is due, in part, to de creased expression of mature proGnRH mRNA. When proGnRH gene expressio n in the mouse brain was examined, the same short splicing variant was observed in the olfactory area and preoptic area-anterior hypothalamu s, But the prevalent transcript in these regions was the mature proGnR H mRNA, In contrast, only the mature proGnRH mRNA was found in the cau dal hypothalamus. These results suggest that alternative splicing may be one of the mechanisms regulating proGnRH gene expression in the ani mal brain.