We have cloned the genes for several human pituitary glycoprotein hormones, as well as hypothalamic releasing hormones, including the beta subunit of human thyrotropin, as well as human prepro-TRH and human gonadotropin-releasing hormone. For the human thyrotropin beta subunit gene we have localized a major thyroid hormone inhibitory element in the first untranslated exon of this gene using a combination of scanning mutational analysis as well as DNA, DNase I footprinting in conjunction with avidin-biotin complex DNA binding. This inhibitory element appeared to be comprised of two distinct half-sites, one located at the 5' end of the exon and another toward the 3' end of the exon. These various results suggest that thyroid hormone receptors binding to at least two sites in the first exon act in conjunction to mediate T3 inhibition of TSH-beta expression. We are currently trying to localize the regions responsible for T3 inhibition of human prepro-TRH gene expression, which seems to be located in the 5' flanking region from -900 to +54. The coding regions of human prepro-TRH and gonadotropin-releasing hormone genes have been completely elucidated. The former hypothalamic hormone gene was found to have 6 repetitive coding sequences for TRH which differs from the number in lower species. The human gonadotropinreleasing hormone gene was found to contain DNA sequences downstream from the transcriptional start site that enhanced expression in a promoter-specific and position-dependent manner. Finally, using a novel polymorphism in the DNA sequence of the gonadotropin-releasing hormone gene, we have shown in a family familial central precocious puberty, as well as in another family with idiopathic hypogonadotropic hypogonadism that these conditions were not related to a fundamental abnormality in this gene. This polymorphism may prove useful in the evaluation of linkage to the GnRH gene in other families with this disorder. These studies will also draw attention to other mechanisms for abnormal pubertal function in man not directly associated with the GnRH gene.
