René Ozon

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The membrane input resistance (R(m)), potential (E(m)), and capacitance (C(m)) of fully grown Xenopus oocytes removed from their follicles have been measured. Before hormonal maturation, R(m), E(m), and C(m) were found to be: 1.86 +/- 0.63 Momega, -49 +/- 17 mV, and 11.9 +/- 4.8 microF/cm2 of apparent surface area. Long-term recording from oocytes in the(More)
During progesterone-induced meiotic maturation of Xenopus oocytes in vitro, 7 morphological stages were defined. Using cytological analysis, nuclear breakdown was divided into three stages. Stage 1 corresponded to basal germinal vesicle breakdown. Stage 2 was characterized by the advent and development of a fibrillar network formed by microtubules at the(More)
Xenopus oocytes were stained by anti-tubulin and anti-MAP1 antibodies during the first meiotic cell division. In the prophase-blocked oocytes, only few microtubules are present around the upper part of the nuclear envelope. These microtubules are resistant to cold, calcium and antimitotic drug treatments. At this stage, monoclonal anti-MAP1 antibody and(More)
During the first meiotic cell division of the Xenopus oocyte, a transient microtubule network appears at the basal part of the disintegrating nucleus. In order to know if this structure plays a role in the formation of the first meiotic spindle, we have studied the actions of Ca2+ ions and taxol during the whole maturation process. We now report that when(More)
The availability of the pure inhibitor of cAMP-dependent protein kinase prompted a re-examination of the inhibitor-induced meiotic maturation of Xenopus laevis oocytes. Injection of the inhibitor (1.5 microM) triggered 100% germinal vesicle breakdown faster than progesterone and slower than the maturation-promoting factor: at 0.15 microM, the inhibitor(More)
In the ovary, oocytes are surrounded by follicle cells and arrested in prophase of meiosis I. Although steroidogenic activity of follicle cells is involved in oogenesis regulation, clear qualitative and quantitative data about the steroid content of follicles are missing. We measured steroid levels of Xenopus oocytes and follicles by gas chromatography-mass(More)
The binding of microtubule associated proteins (MAPs) to free 80 S ribosomes isolated from Xenopus laevis oocytes inhibits in vitro tubulin assembly (Jessus et al., 1984). The inhibition of tubulin polymerisation was shown to be dependent upon GTP. The dose of GTP needed to induce 50% of the maximal effect was 0.5 mM. Furthermore, the inhibition is enhanced(More)