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