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TSO JIA-KE,ZHU GUANG,HSU KUO-GIANG AND WANG YU-LAN (Shanghai Institute of Cell Biology,Academia Sinica)  
Zona pellucida and plasma membrane of the full-grown oocyte of thehibernated common Chinese toad,Bufobufo gargarizans,can be stripped offcompletely after the removal of theovarian membrane and follicular epi-thelium membrane under dissectingmicroscope (Plate Ⅰ,Fig.1—2).Whenthese plasma membrane free oocyteswere embedded in 2% agar blockseparately and immersed in Ringer'ssolution containing progesterone (5μg/ml.),maturation-promoting factor(MPF) was found within the ooplasmsomewhat unexpectedly.Transfer ofthe ooplasm (50 nl.) of these denudedoocytes into the untreated toad oocytethrough microinjection induced theresumption of meiotic division (Fig.1and Table 1) of the later.GVBD,chromosome condensation,first polarbody extrusion and the metaphase figureof the second meiotic division wereevolved normally.If the germinal ve-sicle of the plasma membrane freeoocyte was also removed at the sametime,the maturation promoting effectof progesterone on such denuded oocyte was still the same (Fig.2 and Table2). It was observed that the maturation,promoting activity appeared insome of the denuded oocytes after pro-gesterone treatment for three hours.The longer the hormone treatmenttime,the higher the percentage ofGVBD and normal maturation divisionwere induced in the recipient oocy-tes (Fig.3). During the period of the incubation in Ringer's solution containingprogesterone,no neo-membrane for-mation was observed on the surfaceof the denuded oocytes (Plate Ⅰ,Fig.3).Control oocytes which had re-ceived the ooplasm from the non-treated denuded donors,all posses-sed intact germinal vesicles at anyincubation period (Fig.1—2).Furthermore,a concentration of progesterone hormone which may induce thematuration of the oocytes was notfound in the Ringer's solution aroundthe oocytes. It is evident that the surface membranes (zona pellucida and plasmamembrane),as well as the nucleus ofthe oocyte are dispensable to the progesterone-induced MPF formation.InBufo oocytes,as in Xenopus oocytest,progesterone acts through an initialsite in the cytoplasm.That is to say,the steroid hormone,which is knownto work post-transcriptionally,is capable of regulating oocyte maturation,via an intracellular mechanism.
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