Our work on the hormonal regulation of the human thyrotropin-releasing hormone (TRH) gene has identified a novel thyroid hormone response element through which thyroid hormone inhibits TRH production at the transcriptional level. In the following proposal we will use the molecular techniques gained during my training to fully characterize this negative regulatory element and define its interactions with thyroid hormone receptor (TR) isoforms and TR accessory proteins (TRAPs), such as the retinoid X receptor (RXR). These studies should provide new information on the basic mechanism in which the TR negatively regulates gene expression. The TRH gene also provides an ideal model to explore the syndromes of resistance to thyroid hormone. We hypothesize that dominant negative inhibition by mutant TRs on negative TRES is fundamentally different than on positive TRES, which allows specific mutant TRs to cause resistance only in the hypothalamus and the pituitary while having normal function in the periphery. To extend our work to the TRH neuron itself, we will utilize transgenic technology in collaboration with the Beth Israel Transgenic Facility, to produce a TRH producing neuronal cell line. The development of such a line will have future impact on the regulation of TRH gene expression and our understanding of hypothalamic development.