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Use of reporter genes provides a convenient way to study the activity and regulation of promoters and examine the rate and control of gene transcription. Many reporter genes and transfection methods can be efficiently used for this purpose. To investigate gene regulation and signaling pathway interactions during ovarian follicle development, we have examined promoter activities of several key follicle-regulating genes in the mouse ovary. In this chapter, we describe use of luciferase and beta-galactosidase genes as reporters and a cationic liposome mediated cell transfection method for studying regulation of activin subunit- and estrogen receptor alpha (ERalpha)-promoter activities. We have demonstrated that estrogen suppresses activin subunit gene promoter activity while activin increases ERalpha promoter activity and increases functional ER activity, suggesting a reciprocal regulation between activin and estrogen signaling in the ovary. We also discuss more broadly some key considerations in the use of reporter genes and cell-based transfection assays in endocrine research.

During the mammalian reproductive cycle, the ovary undergoes continuous morphological and biochemical changes that result in the production of mature oocytes and the timed secretion of steroid and polypeptide hormones. The cyclical proliferation of specific cell types, followed by their differentiation, is essential for normal ovarian function. These cell proliferation and differentiation events are controlled by endocrine factors, such as the pituitary gonadotropins, and by paracrine factors produced within the ovary. Among the regulatory factors produced within the ovary are the related polypeptide hormones inhibin and activin. These dimeric proteins were initially isolated as endocrine regulators of pituitary follicle-stimulating hormone (FSH) secretion, but they also function as intraovarian regulatory factors. While the inhibin and activin subunit genes are under complex multihormonal regulation, a predominant aspect of this regulation is exerted by the pituitary gonadotropins FSH and luteinizing hormone (LH).

The peptide hormone GHRH is synthesized in and released from neurosecretory cells in the hypothalamic arcuate nuclei. GHRH acts on pituitary somatotroph cells to stimulate the synthesis and secretion of GH (1–4). The actions of GHRH are opposed by those of somatostatin, a peptide hormone of hypothalamic origin that acts to suppress pituitary growth hormone secretion; together, GHRH and somatostatin are thought to be the predominant mediators of the neural control of GH production (5,6). Although potent synthetic peptide and nonpeptide GH secretagogs have been identified (7,8) and a receptor that binds those compounds has been cloned (9), no endogenous ligands that activate growth hormone secretion through this receptor have been identified.