Abstract 552 Poster Session I, Saturday, 5/1 (poster 305)

Gonadotropin releasing hormone (GnRH) is a hypothalamic neuropeptide that regulates pituitary gonodotropin secretion and thus, reproductive viability. Studies of GnRH gene expression have been difficult due to the paucity of neurons expressing GnRH and their scattered location within the hypothalamus. However, a GnRH-expressing neuronal cell line (i.e., GT1-7) has been established which provides a useful model for studies of GnRH gene regulation. The GT1-7 cell line was derived from tumors generated in transgenic mice expressing an SV40 large tumor antigen driven from the rat GnRH promoter.

A neuron-specific enhancer region has been identified in the rat GnRH gene promoter which is essential for GnRH gene transcription in GT1-7 cells. A number of transcription factors interact with this enhancer including Oct-1, a member of the POU domain family. Mutations within this region bound by Oct-1 in the enhancer reduced GnRH gene transcription.

Interestingly, this region of the GnRH enhancer contains overlapping recognition sequences for other POU domain proteins, such as Brain-2 (Brn-2). Brn-2 is an abundant transcription factor present in developing brain, and has been shown to be essential for neuronal development of the hypothalamic paraventricular nucleus (PVN) and expression of corticotrophin releasing hormone (CRH) in the PVN. In order to assess whether GnRH gene transcription is sensitive to other POU domain proteins, the effects of Brn-2 on GnRH reporter gene transcription were examined in transfected GT1-7 cells. When Brn-2 plasmid was transiently co-transfected with a GnRH reporter gene into GT1-7 cells, there was a profound repression (about 80%) of GnRH reporter gene transcription as measured by a luciferase assay.

SCIP/Oct-6/Tst-1, another member of the POU domain family, has also been found to repress GnRH gene transcription in GT1-7 cells.

Thus, the exact nature of the POU domain protein bound to the GnRH gene enhancer appears to have a dramatic effect on GnRH enhancer activity. Future studies will be directed towards the identity of sequences within the GnRH gene enhancer that may allow closely related transcription factors to be distinguished.

This work is supported by the National Institutes of Health Research Grant RO1 DK47938.