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Episodic Activation of the Rat GnRH Promoter: Role of the Homeoprotein Oct-1

Laboratory of Molecular Dynamics (F.R.B.), Department of Cell Biology and Anatomy, Medical University of South Carolina, Charleston, South Carolina 29425; Department of Medicine, University of Colorado Health Sciences Center and Research Service (M.E.W.), Veterans Affairs Medical Center, Denver, Colorado 80220; and Department of Biochemistry (G.M.L.), Medical University of South Carolina, Charleston, South Carolina 29425

Address all correspondence and requests for reprints to: Dr. Fredric R. Boockfor, Laboratory of Molecular Dynamics, Department of Cell Biology and Anatomy, Medical University of South Carolina, 173 Ashley Avenue, Charleston, South Carolina 29425. E-mail: boockfor{at}musc.edu.

Recent reports demonstrate that the rat GnRH promoter is activated in an episodic fashion in immortalized GnRH neurons, but little information is available on molecular processes that contribute to this phenomenon. In this study, we dissected the regions of the rat GnRH promoter that mediate these effects by testing a series of 5' deletion luciferase reporter constructs on the pattern of photonic emissions from single, living GT1–7 GnRH neuronal cells. Deletion analysis revealed that the region -2012/-1597 that contains the neuron-specific enhancer (NSE) was required for the elaboration of pulses of GnRH promoter activity. The importance of this region was supported by observations that episodic reporter activity could be transferred to a neutral nonpulsatile promoter (Rous sarcoma virus, RSV₁₈₀). Immunoneutralization of Oct-1 as well as mutation of an octamer binding site located at -1787/-1783 (AT-a site) blocked the pulsatile GnRH promoter activity in GT1–7 neuronal cells. Taken together, our findings indicate that episodic GnRH gene expression is a promoter-dependent phenomenon, which is mediated by Oct-1 interaction with regulatory elements in the NSE region.

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