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Cyclical Expression of Egr‐1/NGFI‐A in the Rat Anterior Pituitary: A Molecular Signal for Ovulation?
Author(s) -
Slade,
Jonathan Carter
Publication year - 2000
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1046/j.1365-2826.2000.00512.x
Subject(s) - anterior pituitary , medicine , endocrinology , biology , ovulation , estrous cycle , gene expression , gene , messenger rna , regulation of gene expression , hormone , genetics
Molecular genetic studies of egr‐1 /NGFI‐A have recently established a key role for this immediate early gene in anterior pituitary development, and particularly in transcriptional regulation of the LH β ‐subunit gene. These studies, using null mutant mice, addressed the developmental aspects of gonadotrophin gene regulation by egr‐1 and, because of the limitations of this approach, did not address the role of egr‐1 in adult reproductive physiology. Using the rat, we have now investigated the expression of egr‐1 during the female reproductive cycle, and have found evidence of cyclical changes in anterior pituitary egr‐1 expression, at mRNA, protein, and DNA binding activity levels. Specifically, we have shown that egr‐1 mRNA is significantly elevated during proestrous, and conversely suppressed on the subsequent day of oestrous. We have also demonstrated significantly raised levels of an approximately 70 kDa Egr‐1 immunoreactive protein band during the night of proestrous, together with markedly raised levels of a Egr‐1 consensus sequence DNA binding complex. These studies are indicative of both direct egr‐1 gene regulation by oestrogen, and also regulation by GnRH. Finally, we have sequenced previously uncharacterized regions of the egr‐1 gene and found evidence of a potential oestrogen response element. Our findings are consistent with the hypothesis that Egr‐1 forms at least part of the molecular signal for ovulation in the pituitary.