Helen Kim, M.D.

Molecular Mechanisms Involved in the Regulation of the Mouse Gonadotropin-releasing Hormone (mGnRH) Gene.

Research Summary

Since July 1998, I have been investigating the molecular mechanisms involved in the regulation of the mouse Gonadotropin-releasing Hormone (mGnRH) gene. It has been estimated that only 1000 neurons express GnRH. Initially, I sought to identify the factors that permit GnRH expression in these neurons. Because in vitro studies do not reflect the intricacy of in vivo GnRH gene regulation, I constructed transgenic mice containing different promoter fragments of the mGnRH gene fused to the luciferase reporter gene. With luciferase expression under the control of the mGnRH promoter, mGnRH
gene expression can be detected easily by measuring the luciferase activity in tissue homogenates.

Examination of the mGnRH-luciferase mice revealed another area of investigation. Extremely high levels of luciferase expression were detected in the ovaries collected from mice containing a deletion in the distal part of the mGnRH promoter. The mice bearing the full-length GnRH promoter had minimal ovarian expression, suggesting that sequences in the distal part of the mGnRH promoter mediate repression of mGnRH expression in the ovary.

These mGnRH-luciferase mice provide a powerful tool for examining the regulation of mGnRH expression in vivo. Using these mGnRH-luciferase transgenic mice, I have identified a region of the mGnRH promoter that targets mGnRH expression to the hypothalamus and also defined an ovarian GnRH repressor element in the distal mGnRH promoter region. By characterizing these promoter regions, I will identify transcription factors that regulate mGnRH expression. Eventually, I hope to reveal the mechanisms by which neuronal and ovarian GnRH are differentially regulated.

Selected Papers

Bedford JM, Kim HH. (1993). Cumulus oophorus as a sperm sequestering device, in vivo. J Exp Zool. 265(3):321-8.

Bedford JM, Kim HH. (1999). Sperm/egg binding patterns and oocyte cytology in retrospective analysis of fertilization failure in vitro. Hum Reprod. 8(3):453-63.

Izawa M, Nguyen PH, Kim HH, Yeh J. (1998). Expression of the apoptosis-related genes, caspase-1, caspase-3, DNA fragmentation factor, and apoptotic protease activating factor-1, in human granulosa cells. Fertil Steril. 70(3):549-52.

Radovick S, Kim HH, Stafford DEJ, Wolfe AM, Zakaria M. Transcriptional Development of the Hypothalamic-Pituitary-Gonadal Axis. In: Erica A. Eugster, Ora H. Pescovitz, ed., (2002). Developmental Endocrinology: From Research to Clinical Practice, Totowa, NJ: Humana Press, 243-260.

Kim, HH. Hormonal Contraception. In Margaret H. MacGillvray, Sally Radovick, ed., (2002). Pediatric Endocrinology: A Practical Clinical Guide, Totowa, NJ: Humana Press, 479-508.

Kim HH, Wolfe A, Smith GR, Tobet SA, Radovick S. (2002). Promoter sequences targeting tissue-specific gene expression of hypothalamic and ovarian gonadotropin-releasing hormone in vivo. J Biol Chem. 277(7):5194-202.

Wolfe A, Kim HH, Tobet SA, Stafford DEJ, Radovick S. (2002). Identification of a discrete promoter region of the human GnRH gene that is sufficient for directing neuron-specific expression: a role for POU homeodomain transcription factors. Mol Endocrinol 16:435-449.

Wolfe A, Kim HH, Radovick, S. The GnRH Neuron: Molecular Aspects of Migration, Gene Expression and Regulation. Progress in Brain Research; 2002; 141: 245-259. Prepared September 2003