| Summary: | The role of hydrogen sulfide (H<sub>2</sub>S) is addressed in <i>Xenopus laevis</i> oocytes. Three enzymes involved in H<sub>2</sub>S metabolism, cystathionine β-synthase, cystathionine γ-lyase, and 3-mercaptopyruvate sulfurtransferase, were detected in prophase I and metaphase II-arrested oocytes and drove an acceleration of oocyte meiosis resumption when inhibited. Moreover, meiosis resumption is associated with a significant decrease in endogenous H<sub>2</sub>S. On another hand, a dose-dependent inhibition was obtained using the H<sub>2</sub>S donor, NaHS (1 and 5 mM). NaHS impaired translation. NaHS did not induce the dissociation of the components of the M-phase promoting factor (MPF), cyclin B and Cdk1, nor directly impacted the MPF activity. However, the M-phase entry induced by microinjection of metaphase II MPF-containing cytoplasm was diminished, suggesting upstream components of the MPF auto-amplification loop were sensitive to H<sub>2</sub>S. Superoxide dismutase and catalase hindered the effects of NaHS, and this sensitivity was partially dependent on the production of reactive oxygen species (ROS). In contrast to other species, no apoptosis was promoted. These results suggest a contribution of H<sub>2</sub>S signaling in the timing of amphibian oocytes meiosis resumption.
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