Importin-alpha 2 is critically required for the assembly of ring canals during Drosophila oogenesis

• Published in: Developmental biology 2002-11, Vol.251 (2), p.271-282
• Main Authors: Gorjánácz, Mátyás, Adám, Géza, Török, István, Mechler, Bernard M, Szlanka, Tamás, Kiss, István
• Format: Article
• Language: English
• Subjects: Actins - metabolism; Active Transport, Cell Nucleus; Animals; Carrier Proteins - physiology; Drosophila - physiology; Drosophila Proteins; Female; Infertility; Karyopherins - physiology; Male; Microfilament Proteins; Oogenesis - physiology
• ISSN: 0012-1606
• DOI: 10.1006/dbio.2002.0827

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.