title: Importin-alpha 2 is critically required for the assembly of ring canals during Drosophila oogenesis.
abstract: The interstitial deletion D14 affecting the importin-alpha 2 gene of Drosophila, or imp-alpha 2(D14), causes recessive female sterility characterized by a block of nurse cell-oocyte transport during oogenesis. In wild-type egg chambers, the Imp-alpha 2 protein is uniformly distributed in the nurse cell cytoplasm with a moderate accumulation along the oocyte cortex. Cytochalasin D treatment of wild-type egg chambers disrupts the in vivo association of Imp-alpha 2 with F-actin and results in its release from the oocyte cortex and its transfer into nurse cell nuclei. Binding assay shows that the interaction of Imp-alpha 2 with F-actin, albeit not monomeric actin, requires the occurrence of NLS peptides. Phenotypic analysis of imp-alpha 2(D14) ovaries reveals that the block of nurse cell-oocyte transport results from the occlusion of the ring canals that constitute cytoplasmic bridges between the nurse cells and the oocyte. Immunohistochemistry shows that, although the Imp-alpha2 protein cannot be detected on the ring canals, the Kelch protein, a known ring canal component, fails to bind to ring canals in imp-alpha 2(D14) egg chambers. Since loss-of-function mutations of kelch results in a similar dumpless phenotype, we propose that the Imp-alpha 2 protein plays a critical role in Kelch function by regulating its deposition on ring canals during their assembly.
authors.affiliation: Institute of Genetics, Biological Research Center of the Hungarian Academy of Sciences, Szeged, Hungary.
authors.forename: Mátyás
authors.initials: M
authors.lastname: Gorjánácz
authors.forename: Géza
authors.initials: G
authors.lastname: Adám
authors.forename: István
authors.initials: I
authors.lastname: Török
authors.forename: Bernard M
authors.initials: BM
authors.lastname: Mechler
authors.forename: Tamás
authors.initials: T
authors.lastname: Szlanka
authors.forename: István
authors.initials: I
authors.lastname: Kiss
mesh_terms: D000199:Actins / Q000378:metabolism; D021581:Active Transport, Cell Nucleus; D000818:Animals; D002352:Carrier Proteins / Q000502:physiology; D004330:Drosophila / Q000502:physiology*; D029721:Drosophila Proteins; D005260:Female; D007246:Infertility; D028884:Karyopherins / Q000502:physiology*; D008297:Male; D008840:Microfilament Proteins; D009866:Oogenesis / Q000502:physiology*
chemical_list: D000199:Actins; D002352:Carrier Proteins; D029721:Drosophila Proteins; D028884:Karyopherins; D008840:Microfilament Proteins; C080353:kel protein, Drosophila