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Hypothalamic Expression of Eap1 Is Not Directly Controlled by Ovarian Steroids

Division of Neuroscience (V.M., S.R.O.), Oregon National Primate Research Center, Beaverton, Oregon 97006; and Department of Physiology and Pharmacology (C.M., R.A.S., D.M.D.), Oregon Health and Science University, Portland, Oregon 97239

Address all correspondence and requests for reprints to: Sergio R. Ojeda or Valerie Matagne, Division of Neuroscience, Oregon National Primate Research Center/Oregon Health and Science University, 505 Northwest 185th Avenue, Beaverton, Oregon 97006. E-mail: ojedas{at}ohsu.edu or matagnev{at}ohsu.edu.

A gene termed EAP1 (enhanced at puberty 1) was recently identified as a transcriptional regulator of female neuroendocrine reproductive function. We have now used in vivo and in vitro assays, and the female rat as an animal model, to determine whether Eap1 gene expression is regulated by ovarian steroids. Eap1 mRNA abundance decreases in both the hypothalamus and cerebral cortex during the infantile-juvenile phases of development, but it increases selectively in the hypothalamus at puberty, suggesting that in contrast to the general decline in expression observed in immature animals, the region-specific increase in Eap1 mRNA levels that occurs at puberty might be elicited by ovarian steroids. This is, however, not the case, because hypothalamic Eap1 mRNA levels increase at the expected time of puberty in rats ovariectomized at the beginning of the juvenile period. Although a subpopulation of EAP1-containing cells in the medial basal hypothalamus (MBH) and preoptic area express estrogen receptor- (ER), the 5'-flanking region of the rat Eap1 (rEap1) gene does not contain a complete estrogen-responsive element, and no such estrogen-responsive element is detected within 100 kb of the rEap1 locus. Functional promoter assays showed that neither estradiol (E₂) alone nor a combination of E₂ plus progesterone increases rEap1 gene transcription. Likewise, E₂ administered to ovariectomized immature rats elicited a robust surge of LH but increased neither preoptic area nor MBH Eap1 mRNA levels. E₂/progesterone-treated rats showed a massive elevation in plasma LH but only a modest increase in Eap1 mRNA levels, limited to the MBH. These results indicate that hypothalamic Eap1 expression is not directly controlled by ovarian steroids and suggest that Eap1 expression increases at puberty driven by ovary-independent, centrally initiated events.