Many peripheral reproductive tissues have been found to contain gonadotrophin-releasing hormone (GnRH) and express the GnRH gene at low levels, presumably because the hormone functions in a paracrine/autocrine fashion. This study was designed to investigate and characterize GnRH gene expression in human endometrial tissue at different stages of the endometrial cycle. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis together with Southern blot assay demonstrated that human endometrial tissue expresses the proGnRH gene. RNA samples from endometrial tissue were analysed with two pairs of oligonucleotide primers. Both gave a doublet 870 bases apart at the expected sizes, indicating that both the upstream and downstream transcriptional start sites of the GnRH gene are used in endometrial tissue and that transcripts with and without intron 1 were produced. Our data also demonstrated that utilization of the two promoters varies with the stage of the endometrial cycle. The largest difference came from the mRNA transcribed from the downstream promoter and without intron 1. This mRNA was expressed at a very low level during the proliferative phase and dramatically increased almost 10-fold (P <0.01) during the early secretory phase, and subsequently decreased 5-fold during the late secretory stage. The presence of GnRH mRNA in the endometrium, as well as the differential expression of the GnRH gene during the early secretory phase provides physiological evidence that human GnRH may play a paracrine/autocrine function in the human uterus.
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