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      Activin A Regulation of Gonadotropin-Releasing Hormone Synthesis and Release in vitro

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          Activin is essential for the regulation of normal mammalian reproductive function at both the pituitary and gonadal levels. However, its central actions in the control of the hypothalamic-pituitary-gonadal axis remain largely unexplored. The present study aims to determine whether activin could regulate the reproductive axis at the level of the hypothalamus, through control of the GnRH neuroendocrine system. Using the GnRH-secreting GT1-7 neuronal cell line as a model system, we demonstrate expression of mRNAs encoding activin receptor types I, IB, and II. We examined the effects of activin A on GnRH protein secretion and mRNA levels in GT1-7 cells. Treatment with rh-activin A regulated both GnRH protein secretion and GnRH mRNA expression in the GT1-7 cells in a time-dependent fashion. Using transient transfection assays, we explored a potential transcriptional basis for these changes. Activin A increased reporter gene activity driven by minimal GnRH enhancer and promoter elements, suggesting that activin may regulate GnRH gene expression at the level of transcription. Lastly, activin A treatment of male rat hypothalami, in vitro, increased GnRH protein secretion. Collectively, molecular and physiological evidence support the presence of an activin system which might act at a hypothalamic site to regulate mammalian reproduction via activation of GnRH synthesis and release.

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          Most cited references 6

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          Expression cloning of an activin receptor, a predicted transmembrane serine kinase.

          Activins are involved in the regulation of multiple biological events, ranging from early development to pituitary function. To characterize the cellular mechanisms involved in these processes, cDNAs coding for an activin receptor were cloned from AtT20 mouse corticotropic cells by screening COS cell transfectants for binding of 125I-activin A. The cDNAs code for a protein of 494 amino acids comprising a ligand-binding extracellular domain, a single membrane-spanning domain, and an intracellular kinase domain with predicted serine/threonine specificity. 125I-activin A binds to transfected COS cells with an affinity of 180 pM and can be competed by activin A, activin B, and inhibin A, but not by transforming growth factor beta 1. The kinase domain, but not the extracellular sequence, of the activin receptor is most closely related to the C. elegans daf-1 gene product, a putative transmembrane serine/threonine-specific protein kinase for which the ligand is not known.
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            Segmentation and the origin of regional diversity in the vertebrate central nervous system

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              Regulation of transforming growth factor beta- and activin-induced transcription by mammalian Mad proteins.

              Members of the transforming growth factor beta (TGF-beta) superfamily are involved in diverse physiological activities including development, tissue repair, hormone regulation, bone formation, cell growth, and differentiation. At the cellular level, these functions are initiated by the interaction of ligands with specific transmembrane receptors with intrinsic serine/threonine kinase activity. The signaling pathway that links receptor activation to the transcriptional regulation of the target genes is largely unknown. Recent work in Drosophila and Xenopus signaling suggested that Mad (Mothers against dpp) functions downstream of the receptors of the TGF-beta family. Mammalian Mad1 has been reported to respond to bone morphogenetic protein (BMP), but not to TGF-beta or activin. We report here the cloning and functional studies of a novel mammalian Mad molecule, Mad3, as well as a rat Mad1 homologue. Overexpression of Mad3 in a variety of cells stimulated basal transcriptional activity of the TGF-beta/activin-responsive reporter construct, p3TP-Lux. Furthermore, expression of Mad3 could potentiate the TGF-beta- and activin-induced transcriptional stimulation of p3TP-Lux. By contrast, overexpression of Mad1 inhibited the basal as well as the TGF-beta/activin induced p3TP-Lux activity. These findings, therefore, support the hypothesis that Mad3 may serve as a mediator linking TGF-beta/activin receptors to transcriptional regulation.

                Author and article information

                S. Karger AG
                October 1999
                14 October 1999
                : 70
                : 4
                : 246-254
                Department of Reproductive Medicine, University of California, San Diego, La Jolla, Calif., USA
                54483 Neuroendocrinology 1999;70:246–254
                © 1999 S. Karger AG, Basel

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                Page count
                Figures: 6, References: 45, Pages: 9
                Reproductive Neuroendocrinology


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