Oestrogenic regulation of an egr-1 transgene in rat anterior pituitary.
The C(2)H(2) zinc-finger transcription factor Egr-1 has previously been shown to play an essential role within the endocrine system as a molecular determinant of LH beta-subunit synthesis in anterior pituitary gonadotrophs. The extent to which Egr-1 may be a dynamic mediator of changes in gonadotroph function during the oestrous cycle is currently unclear. We have recently produced a novel rat transgenic model of egr-1 gene function in which proximal regions of the rat egr-1 gene drive expression of a reporter gene. In the present study, we have investigated the expression and physiological regulation of our egr-1/d4 enhanced green fluorescent protein (EGFP) transgene in the female rat pituitary gland. In situ hybridization analysis has revealed anterior pituitary-specific expression that is limited to a sub-population of cells that includes immunohistochemically defined gonadotrophs. Expression of the transgene is up-regulated 5-fold following ovariectomy. The transgene also exhibits regulated expression during the oestrous cycle, mRNA levels being significantly raised on pro-oestrus. Using an explant culture system, we have also demonstrated a direct stimulatory effect of 17beta-oestradiol on anterior pituitary transgene and egr-1 expression. The acute response of egr-1 to an oestrogenic stimulus is attenuated by the MEK (MAPK kinase) inhibitor U0126, and is accompanied by increased levels of phospho-p44/42 MAPK protein, suggesting regulation of egr-1 through a MAPK-linked pathway in the pituitary. These findings provide further evidence of cyclical endocrine regulation of egr-1 in the rat, demonstrate that proximal sequences of the egr-1 gene mediate endocrine-regulated expression, and indicate a novel pathway through which pituitary transcriptional responses to oestrogen may be mediated.
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School of Biosciences, Cardiff University, PO Box 911, Museum Avenue, Cardiff CF10 3US, UK.
Carter
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D000818:Animals; D030801:Animals, Genetically Modified; D046508:Culture Techniques; D004967:Estrogens / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000502:physiology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010052:Ovariectomy; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D019076:Transgenes
D004967:Estrogens; D008164:Luminescent Proteins; D049452:Green Fluorescent Proteins; D020928:Mitogen-Activated Protein Kinases