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J Cell Biol 2007 Jan 29;1763:295-305. doi: 10.1083/jcb.200605199.
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A centriole- and RanGTP-independent spindle assembly pathway in meiosis I of vertebrate oocytes.

Dumont J , Petri S , Pellegrin F , Terret ME , Bohnsack MT , Rassinier P , Georget V , Kalab P , Gruss OJ , Verlhac MH .

Spindle formation is essential for stable inheritance of genetic material. Experiments in various systems indicate that Ran GTPase is crucial for meiotic and mitotic spindle assembly. Such an important role for Ran in chromatin-induced spindle assembly was initially demonstrated in Xenopus laevis egg extracts. However, the requirement of RanGTP in living meiotic cells has not been shown. In this study, we used a fluorescence resonance energy transfer probe to measure RanGTP-regulated release of importin beta. A RanGTP-regulated gradient was established during meiosis I and was centered on chromosomes throughout mouse meiotic maturation. Manipulating levels of RanGTP in mice and X. laevis oocytes did not inhibit assembly of functional meiosis I spindles. However, meiosis II spindle assembly did not tolerate changes in the level of RanGTP in both species. These findings suggest that a mechanism common to vertebrates promotes meiosis I spindle formation in the absence of chromatin-induced microtubule production and centriole-based microtubule organizing centers.

PubMed ID: 17261848
PMC ID: PMC2063956
Article link: J Cell Biol

Species referenced: Xenopus laevis
Genes referenced: dnai1 kpnb1 pbrm1 ran ranbp1 rcc1 tub

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References [+] :
Askjaer, Ran GTPase cycle and importins alpha and beta are essential for spindle formation and nuclear envelope assembly in living Caenorhabditis elegans embryos. 2002, Pubmed