Autoradiographic localization of specific binding of meiosis-activating sterol to cumulus-oocyte complexes from marmoset, cow, and mouse.
The sterol, 4,4-dimethyl-5alpha-cholesta-8,14,24-trien-3beta-ol (FF-MAS), isolated from human follicular fluid, can induce resumption of meiosis in denuded and cumulus-enclosed mouse oocytes inhibited by hypoxanthine, IBMX, or dibutyric cyclic adenosine monophosphate. In this study the distribution of FF-MAS binding sites in denuded oocytes and in cumulus-oocyte complexes (COCs) was studied using light microscopic (LM) and transmission electron microscopic (TEM) autoradiography in marmoset, cow, and mouse oocytes. Denuded (n = 39) and cumulus-enclosed (n = 28) marmoset, cow, and mouse oocytes were cultured in the presence of [3H]FF-MAS with and without excess of unlabeled FF-MAS, respectively. In denuded oocytes LM autoradiography demonstrated specific binding to the oolemma and zona pellucida and, to some extent, the cytoplasm. In the nucleus, no specific binding of [3H]FF-MAS was demonstrated. In some COCs the labeling was dispersed throughout the zona pellucida, the oolemma, and the cytoplasm as well as the cumulus cells; whereas in others, only the outer part of the cumulus cells were labeled. TEM autoradiograms of denuded cow oocytes (n = 6) demonstrated that specific [3H]FF-MAS binding was closely related to the oolemma and that a low level of [3H]FF-MAS binding to cumulus cell remnants was present. In conclusion, specific binding of FF-MAS is predominant at the oolemma of denuded oocytes, suggesting the existence of a plasma membrane-associated molecule with affinity for FF-MAS (i.e., a putative FF-MAS receptor).
Faerge
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Pharmacological Research 3, Pharmacology, Health Care Discovery, Novo Nordisk A/S, Novo Nordisk Park, G 8.1.39, Må, 2760 Måløv, Denmark. ingf@novo.dk
Grøndahl
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Ottesen
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Hyttel
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D000818:Animals; D001345:Autoradiography; D002144:Callithrix / Q000378:metabolism*; D002417:Cattle; D002782:Cholestenes / Q000138:chemical synthesis / Q000378:metabolism*; D005260:Female; D051379:Mice; D008854:Microscopy, Electron; D009865:Oocytes / Q000378:metabolism* / Q000648:ultrastructure; D013045:Species Specificity; D013347:Subcellular Fractions / Q000378:metabolism
D002782:Cholestenes; C100324:4,4-dimethylcholesta-8,14,24-trienol