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.

• Keywords
• RanGTP, importazole, importin β, meiosis I, oocyte,
• MeSH
• Spindle Apparatus physiology   MeSH
• beta Karyopherins genetics   metabolism   MeSH
• Nuclear Proteins genetics   metabolism   MeSH
• Meiosis physiology   MeSH
• Microtubules metabolism   MeSH
• Mutation MeSH
• Mice MeSH
• Oocytes cytology   metabolism   MeSH
• Cell Cycle Proteins genetics   metabolism   MeSH
• ran GTP-Binding Protein genetics   metabolism   MeSH
• Chromosome Segregation MeSH
• Guanine Nucleotide Exchange Factors genetics   metabolism   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• beta Karyopherins MeSH
• Nuclear Proteins MeSH
• Cell Cycle Proteins MeSH
• ran GTP-Binding Protein MeSH
• Rcc1 protein, mouse MeSH Browser
• Guanine Nucleotide Exchange Factors MeSH