Role of GRAF in regulating actin dynamics during Drosophila cellularization

Abstract

The spatiotemporal regulation of actomyosin contractility is critical for cell migration, wound healing, cytokinesis and morphogenesis. The assembly and activity of actomyosin networks are under the regulation of Rho-GTP which is in turn regulated by the balance between activation by GEFs and inhibition by GAPs. While the activation of RhoA by Rho-GEF2 is well studied in Drosophila cellularization, the major Rho-GAP in cellularization had not been described until recently. GRAF- a multidomain protein with BAR, PH, RhoGAP and SH3 domains is the major RhoGAP in cellularization. Here, we describe the role of GRAF’s domains in restricting the contractility of the actomyosin network and recruiting GRAF itself to the furrow tip. All of GRAF’s domains are important in the regulation of the rate of constriction. The BAR and SH3 domains of GRAF are important for the membrane recruitment and/or stabilization of GRAF, whereas the RhoGAP and PH domains are important for timely membrane dissociation. We also show that GRAF plays a role in the restriction of recruitment of actin binding proteins Anillin and the Septin Peanut. The membrane recruitment of the formin Diaphanous is dependent on GRAF. GRAF therefore plays a significant role in not only regulating Myosin II recruitment but also timely recruitment of actin remodelling proteins that have been known to play significant roles in regulating contractile ring constriction at the cleavage. Future analysis of the domains that are responsible for these phenotypes will reveal the mechanism by which GRAF regulates constriction at the cleavage furrow.