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Updated: Jan 5, 2026
Meiotic Spindle Assessment in Mouse Oocytes by siRNA-mediated Silencing
Published on: October 11, 2015
RanGTP and importin β regulate meiosis I spindle assembly and function in mouse oocytes
David Drutovic1, Xing Duan2,3, Rong Li2,3
1Institute of Animal Physiology and Genetics of the Czech Academy of Sciences, Libechov, Czech Republic.
Abstract:
Homologous chromosome segregation during meiosis I (MI) in mammalian oocytes is carried out by the acentrosomal MI spindles. Whereas studies in human oocytes identified Ran GTPase as a crucial regulator of the MI spindle function, experiments in mouse oocytes questioned the generality of this notion. Here, we use live-cell imaging with fluorescent probes and Förster resonance energy transfer (FRET) biosensors to monitor the changes in Ran and importin β signaling induced by perturbations of Ran in mouse oocytes while examining the MI spindle dynamics. We show that unlike RanT24N employed in previous studies, a RanT24N, T42A double mutant inhibits RanGEF without perturbing cargo binding to importin β and disrupts MI spindle function in chromosome segregation. Roles of Ran and importin β in the coalescence of microtubule organizing centers (MTOCs) and MI spindle assembly are further supported by the use of the chemical inhibitor importazole, whose effects are partially rescued by the GTP hydrolysis-resistant RanQ69L mutant. These results indicate that RanGTP is essential for MI spindle assembly and function both in humans and mice.
Insights
Ran GTPase is essential for homologous chromosome segregation during meiosis I in both human and mouse oocytes. This study clarifies its role in spindle assembly and function, resolving previous discrepancies between species.
Area of Science:
- Cell Biology
- Molecular Biology
- Reproductive Biology
Background:
- Meiosis I (MI) spindle function in mammalian oocytes is crucial for homologous chromosome segregation.
- Previous studies suggested Ran GTPase regulates MI spindle function in human oocytes, but this was questioned in mouse oocytes.
- Understanding conserved mechanisms of MI spindle regulation is vital for reproductive biology.
Purpose of the Study:
- To investigate the role of Ran GTPase and importin β signaling in mouse oocyte meiosis I spindle assembly and function.
- To resolve conflicting findings regarding Ran GTPase's role in mouse oocytes compared to human oocytes.
- To elucidate the molecular mechanisms underlying acentrosomal spindle organization in mammalian oocytes.
Main Methods:
- Live-cell imaging utilizing fluorescent probes and Förster resonance energy transfer (FRET) biosensors.
- Perturbation of Ran GTPase signaling using specific mutants (e.g., RanT24N, T42A double mutant) and chemical inhibitors (importazole).
- Monitoring of meiosis I spindle dynamics and chromosome segregation in mouse oocytes.
Main Results:
- A specific Ran mutant (RanT24N, T42A) inhibited RanGEF activity without affecting importin β cargo binding, disrupting MI spindle function and chromosome segregation.
- Ran GTPase and importin β are essential for microtubule organizing center (MTOC) coalescence and MI spindle assembly.
- The effects of importazole were partially rescued by a GTP hydrolysis-resistant Ran mutant (RanQ69L), further supporting the role of RanGTP.
Conclusions:
- Ran GTPase is indispensable for the assembly and function of the meiosis I spindle in mammalian oocytes, including mice.
- The findings reconcile previous discrepancies, establishing a conserved role for Ran GTPase in homologous chromosome segregation across species.
- Ran GTPase signaling is a critical regulator of acentrosomal spindle organization and chromosome segregation during oocyte meiosis.
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