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Sex Differences in Estrogen-Dependent Transcription of Gonadotropin-Releasing Hormone (GnRH) Gene Revealed in GnRH Transgenic Mice

Laboratory of Neuroendocrinology (N.R.T., R.S., A.E.H.), The Babraham Institute, Cambridge CB2 4AT, United Kingdom; and Centre for Neuroendocrinology and Department of Physiology (A.E.H.), University of Otago School of Medical Sciences, Dunedin, New Zealand

Address all correspondence and requests for reprints to: Prof. Allan E. Herbison, Department of Physiology, University of Otago School of Medical Sciences, P.O. Box 913, Dunedin, New Zealand. E-mail: allan.herbison{at}stonebow.otago.ac.nz.

The mechanisms through which gonadal steroids exert feedback actions on the activity of the GnRH neurons are not understood. Using a series of GnRH-LacZ transgenic mice we have examined the manner in which gonadal steroids suppress GnRH mRNA expression in male and female mice. The long-term gonadectomy of 5.5-GNZ-3.5 transgenic mice resulted in significant increases in cellular GnRH mRNA expression (P < 0.05) and plasma LH concentrations (P < 0.01) in both sexes. However, cellular levels of LacZ mRNA and ß-galactosidase, which provide an index of GnRH gene transcription, were only elevated in males after gonadectomy. This sexually differentiated response was also observed in mice gonadectomized for 2 wk. Estrogen replacement in gonadectomized males returned transgene expression to intact levels. Experiments in transgenic mice with 3' and 5' deleted GnRH-LacZ constructs revealed that the suppressive influence of estrogen on LacZ transcription in the male required a critical element located between -5.2 and -1.7 kb of the GnRH promoter. These studies show that the suppression of GnRH mRNA expression by estrogen in the male involves a decrease in GnRH gene transcription that is dependent on a distal GnRH promoter element. The same mechanism does not exist in females, indicating that gonadal steroids suppress GnRH mRNA levels in a sexually dimorphic manner.

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