TRANSCRIPTIONAL REGULATION OF GONADOTROPIN BETA SUBUNITS DURING DEVELOPMENT

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The gonadotropins, luteinizing hormone (LH), follicle-stimulating hormone (FSH) and chorionic gonadotropin (CG), are essential to mammalian reproduction. LH and FSH are synthesized and secreted from the anterior pituitary gland function to regulate gonadal gametogenesis and steroidogenesis, while CG is synthesized and secreted from the placenta and has a role in maintaining pregnancy. The gonadotropins are heterodimeric glycoprotein hormones composed of a common alpha-subunit noncovalently linked to a unique beta-subunit. A considerable amount of attention has been focused on regulation of expression of the alpha- subunit gene, however, little is known about the mechanisms that regulate expression of the gonadotropin beta-subunits. This has been due to a lack of cell lines that express gonadotropin beta-subunits. Transgenic mice have proven to be extremely valuable for the study of the alpha-subunit and recently have been reported to be a useful model in which to investigate regulation of the beta-subunits. These studies have examined transgene expression in adult mice, but have failed to address spatiotemporal expression patterns. The overall goal of the present proposal is to identify regions in the LHbeta and FSHbeta proximal promoters that direct the appropriate spatiotemporal pattern of expression in transgenic mice. Accordingly, experiments have been proposed to: 1) identify the segment of the equine LH/CGbeta-subunit gene that directs the correct spatial and temporal pattern of expression in the pituitary and to determine whether this region of the gene is also responsible for GnRH regulation of gene expression, and 2) define a small region of the ovine FSHbeta-subunit proximal promoter that retains the correct temporal pattern of gonadotrope-specific expression. Transgenes will be evaluated in adult mice for gonadotrope-specific expression and during embryonic development for the correct onset of expression as well as gonadotrope-specific expression. This segment of proximal promoter must then contain the DNA response elements responsible for directing the correct pattern of gene expression. These promoter fragments will subsequently serve as valuable test constructs in which the physiological relevance of various cis- elements can be evaluated. Several such elements have been identified in the eLH/CGbeta and oFSHbeta proximal promoters and await such testing. The functional significance of these putative elements in the oFSHbeta gene have not been determined.