Expression of gonadotropin-releasing hormone and prothymosin-alpha messenger ribonucleic acid in the ovary.

GnRH exerts paradoxical effects on ovarian cells through specific receptors. Based on observed direct effects of GnRH and its antagonists on ovarian functions, the presence of endogenous ovarian GnRH-like peptide(s) has been postulated. In an attempt to detect the ovarian expression of GnRH or related genes at the RNA level, we used the reverse transcription-polymerase chain reaction (RT-PCR) to amplify GnRH mRNA levels. Total RNA from rat ovaries was converted to first strand cDNA using reverse transcriptase and amplified in PCR using a pair of primers complementary to the rat GnRH cDNA. The DNA products obtained were subcloned into plasmid vectors, and their sequences were determined. The most prominent PCR product of 462 basepairs (bp) was unexpectedly identified as a fragment of prothymosin-alpha cDNA previously found in the spleen. This cDNA was obtained because of an identical 10 bp match with the 3' end of one of the GnRH primers. Northern blot analyses using the cloned prothymosin-alpha cDNA as probe revealed the presence of mRNA for this factor in ovary, thymus, testis, placenta, and hypothalamus. RT-PCR amplification of hypothalamus and granulosa cell messages indicated the presence of a 244-bp product with a sequence identical to that of GnRH. To further confirm the presence of GnRH messages in the ovary, a second set of GnRH primers was used. PCR amplification of cDNA from hypothalamus, granulosa cells, and whole ovary yielded a 241-bp product identical to the authentic GnRH sequence based on analysis on both strands. In contrast, no PCR product was evident after amplification of thyroid cDNA. Our data demonstrated the expression of mRNA for GnRH and prothymosin-alpha in the ovary. Although the exact ovarian role of the immune hormone awaits further study, the detection of GnRH transcript in the ovary suggests potential intragonadal roles of this decapeptide.