Dunk Regulates Cortical Localization of Myosin II during Drosophila Cellularization through Interaction with the Scaffolding Protein Anillin
Authors: Jiayang Chen; Bing He; Melissa Wang
Affiliation: Dartmouth College
Keywords: q. epithelial sheets; a. cytoskeleton
Cleavage is a common step of early embryonic development, generating a monolayer of epithelial cells at the surface of the embryo called “blastoderm”. In Drosophila, this process is achieved by cellularization, a special form of cytokinesis. Similar to typical cytokinesis, cellularization is initiated by recruiting non-muscle myosin II (“myosin”) to the cleavage furrows. Myosin first forms an interconnected hexagonal array at the base of the invaginating cleavage furrows and subsequently reorganizes into individual contractile rings. We have previously identified a gene dunk that promotes myosin retention at the basal array during early cellularization, but the underlying mechanism is unclear. In this work, we performed a genome-wide yeast two-hybrid screen and identified anillin (Scraps in Drosophila), a conserved cytokinesis scaffolding protein, as the primary binding partner of Dunk. Anillin has been reported to regulate the formation of cytokinetic rings during cellularization, but it is unclear whether it regulates the basal myosin array before ring formation. We found that anillin extensively colocalized with the basal myosin array during early cellularization. This colocalization could be detected as early as the onset of cellularization when myosin was first recruited to the cortex as discrete puncta. During the formation of nascent cleavage furrows, anillin and myosin remained colocalized in the cortical puncta as they moved to the cleavage furrows. In anillin mutant, myosin showed a biased localization to the vertices of the basal array and was depleted from edges, closely resembling the myosin phenotype in dunk mutant embryos. Dunk and anillin also display functional interactions. In dunk mutant embryos, the localization of anillin at the basal array was severely disrupted. Furthermore, embryos doubly heterozygous for anillin and dunk showed synthetic defects during cellularization. Finally, dunk and anillin mutants showed similar synthetic phenotypes when combined with mutations in Bottleneck, an actin-bundling protein functioning to restrain actomyosin contractility during cellularization. Together, our results suggest that Dunk regulates myosin at the basal array by interacting with anillin and regulating its cortical localization. Our work demonstrates a previously unappreciated role for anillin in regulating cortical myosin dynamics in early cellularization and may shed light on the regulation of myosin in other cytokinetic processes.