Dataset Information

Specific Cooperation Between Imp-?2 and Imp-?/Ketel in Spindle Assembly During Drosophila Early Nuclear Divisions.

ABSTRACT: The multifunctional factors Imp-? and Imp-? are involved in nuclear protein import, mitotic spindle dynamics, and nuclear membrane formation. Furthermore, each of the three members of the Imp-? family exerts distinct tasks during development. In Drosophila melanogaster, the imp-?2 gene is critical during oogenesis for ring canal assembly; specific mutations, which allow oogenesis to proceed normally, were found to block early embryonic mitosis. Here, we show that imp-?2 and imp-? genetically interact during early embryonic development, and we characterize the pattern of defects affecting mitosis in embryos laid by heterozygous imp-?2(D14) and imp-?(KetRE34) females. Embryonic development is arrested in these embryos but is unaffected in combinations between imp-?(KetRE34) and null mutations in imp-?1 or imp-?3. Furthermore, the imp-?2(D14)/imp-?(KetRE34) interaction could only be rescued by an imp-?2 transgene, albeit not imp-?1 or imp-?3, showing the exclusive imp-?2 function with imp-?. Use of transgenes carrying modifications in the major Imp-?2 domains showed the critical requirement of the nuclear localization signal binding (NLSB) site in this process. In the mutant embryos, we found metaphase-arrested mitoses made of enlarged spindles, suggesting an unrestrained activity of factors promoting spindle assembly. In accordance with this, we found that Imp-?(KetRE34) and Imp-?(KetD) bind a high level of RanGTP/GDP, and a deletion decreasing RanGTP level suppresses the imp-?(KetRE34) phenotype. These data suggest that a fine balance among Imp-?2, Imp-?, RanGTP, and the NLS cargos is critical for mitotic progression during early embryonic development.

SUBMITTER: Viragh E

PROVIDER: S-EPMC3276186 | biostudies-literature | 2012 Jan

REPOSITORIES: biostudies-literature

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Publications

Specific Cooperation Between Imp-α2 and Imp-β/Ketel in Spindle Assembly During Drosophila Early Nuclear Divisions.

Virágh Erika E Gorjánácz Mátyás M Török István I Eichhorn Tolga T Kallakuri Sowjanya S Szlanka Tamás T Kiss István I Mechler Bernard M BM

G3 (Bethesda, Md.) 20120101 1

The multifunctional factors Imp-α and Imp-β are involved in nuclear protein import, mitotic spindle dynamics, and nuclear membrane formation. Furthermore, each of the three members of the Imp-α family exerts distinct tasks during development. In Drosophila melanogaster, the imp-α2 gene is critical during oogenesis for ring canal assembly; specific mutations, which allow oogenesis to proceed normally, were found to block early embryonic mitosis. Here, we show that imp-α2 and imp-β genetically int ...[more]

PMID: 22384376

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Project description:Previous data suggested that anastral spindles, morphologically similar to those found in oocytes, can assemble in a centrosome-independent manner in cells that contain centrosomes. It is assumed that the microtubules that build these acentrosomal spindles originate over the chromatin. However, the actual processes of centrosome-independent microtubule nucleation, polymerisation, and sorting have not been documented in centrosome-containing cells. We have identified two experimental conditions in which centrosomes are kept close to the plasma membrane, away from the nuclear region, throughout meiosis I in Drosophila spermatocytes. Time-lapse confocal microscopy of these cells labelled with fluorescent chimeras reveals centrosome-independent microtubule nucleation, growth, and sorting into a bipolar spindle array over the nuclear region, away from the asters. The onset of noncentrosomal microtubule nucleation is significantly delayed with respect to nuclear envelope breakdown and coincides with the end of chromosome condensation. It takes place in foci that are close to the membranes that ensheath the nuclear region, not over the condensed chromosomes. Metaphase plates are formed in these spindles, and, in a fraction of them, some degree of polewards chromosome segregation takes place. In these cells that contain both membrane-bound asters and an anastral spindle, the orientation of the cytokinesis furrow correlates with the position of the asters and is independent of the orientation of the spindle. We conclude that the fenestrated nuclear envelope may significantly contribute to the normal process of spindle assembly in Drosophila spermatocytes. We also conclude that the anastral spindles that we have observed are not likely to provide a robust back-up able to ensure successful cell division. We propose that these anastral microtubule arrays could be a constitutive component of wild-type spindles, normally masked by the abundance of centrosome-derived microtubules and revealed when asters are kept away. These observations are consistent with a model in which centrosomal and noncentrosomal microtubules contribute to the assembly and are required for the robustness of the cell division spindle in cells that contain centrosomes.

Dataset Information

Specific Cooperation Between Imp-?2 and Imp-?/Ketel in Spindle Assembly During Drosophila Early Nuclear Divisions.

Publications

Specific Cooperation Between Imp-α2 and Imp-β/Ketel in Spindle Assembly During Drosophila Early Nuclear Divisions.

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