Anillin-mediated Targeting of Peanut to Pseudocleavage Furrows Is Regulated by the GTPase Ran

Rosalind V. Silverman-Gavrila,* ${dagger}$ Karen G. Hales, ${ddagger}$ ${sect}$ and Andrew Wilde*

^*Department of Molecular Genetics, University of Toronto, M5S 1A8 Toronto, Ontario, Canada; Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599-3280

Monitoring Editor: Yu-Li Wang

During early development in Drosophila,pseudocleavage furrows in the syncytial embryo prevent contactbetween neighboring spindles, thereby ensuring proper chromosomesegregation. Here we demonstrate that the GTPase Ran regulatespseudocleavage furrow organization. Ran can exert control onpseudocleavage furrows independently of its role in regulatingthe microtubule cytoskeleton. Disruption of the Ran pathwayprevented pseudocleavage furrow formation and restricted thedepth and duration of furrow ingression of those pseudocleavagefurrows that did form. We found that Ran was required for thelocalization of the septin Peanut to the pseudocleavage furrow,but not anillin or actin. Biochemical assays revealed that thedirect binding of the nuclear transport receptors importin ${alpha}$ and ${beta}$ to anillin prevented the binding of Peanut to anillin.Furthermore, RanGTP reversed the inhibitory action of importin ${alpha}$ and ${beta}$ . On expression of a mutant form of anillin that lackedan importin ${alpha}$ and ${beta}$ binding site, inhibition of Ran no longerrestricted the depth and duration of furrow ingression in thosepseudocleavage furrows that formed. These data suggest thatanillin and Peanut are involved in pseudocleavage furrow ingressionin syncytial embryos and that this process is regulated by Ran.

Present addresses: Division of Cell and Molecular Biology, Toronto General Research Institute; Department of Biology, Davidson College, Davidson NC 28035.

Address correspondence to: Andrew Wilde (andrew.wilde{at}utoronto.ca)