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Steroids. 2006 Apr;71(4):310-6. Epub 2005 Nov 14.

Progestin, estrogen and androgen G-protein coupled receptors in fish gonads.

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University of Texas at Austin, Marine Science Institute, Port Aransas, 78374, USA.


The identities of the membrane receptors mediating the majority of rapid, cell surface-initiated, nongenomic (i.e. nonclassical) steroid actions described to date are unclear. Two novel 7-transmembrane spanning proteins, representing two distinct classes of steroid membrane receptors, membrane progestin receptor alpha (mPRalpha) and a membrane estrogen receptor (mER), GPR30, have recently been identified in several vertebrate species. Evidence that both receptors activate G-proteins and function as G-protein coupled receptors (GPCRs) is briefly reviewed. New data on progestin actions on fish gametes suggest a widespread involvement of mPRalpha in oocyte maturation and sperm hyperactivity in this vertebrate group. Information on the second messenger pathways activated upon estrogen binding to a membrane estrogen receptor in croaker gonads and preliminary evidence for the presence of a GPR30-like protein in fish gonads are discussed. Finally, initial characterization of the ligand binding, G-protein activation and molecular size of a membrane androgen receptor (mAR) in croaker ovaries suggests the presence of a third unique steroid receptor in fish gonads that also may function as a GPCR.

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