Formin-mediated actin polymerization cooperates with Mushroom body defect (Mud)–Dynein during Frizzled–Dishevelled spindle orientation

Abstract

SummaryTo position the mitotic spindle, cytoskeletal components must be coordinated to generate cortical forces on astral microtubules. Although the dynein motor is common to many spindle orientation systems, 'accessory pathways' are often also required. In this work, we identified an accessory spindle orientation pathway in Drosophila that functions with Dynein during planar cell polarity, downstream of the Frizzled (Fz) effector Dishevelled (Dsh). Dsh contains a PDZ ligand and a Dynein-recruiting DEP domain that are both required for spindle orientation. The Dsh PDZ ligand recruits Canoe/Afadin and ultimately leads to Rho GTPase signaling mediated through RhoGEF2. The formin Diaphanous (Dia) functions as the Rho effector in this pathway, inducing F-actin enrichment at sites of cortical Dsh. Chimeric protein experiments show that the Dia-actin accessory pathway can be replaced by an independent kinesin (Khc73) accessory pathway for Dsh-mediated spindle orientation. Our results define two 'modular' spindle orientation pathways and show an essential role for actin regulation in Dsh-mediated spindle orientation.

Robust Asymmetric Localization of Planar Polarity Proteins Is Associated with Organization into Signalosome-like Domains of Variable Stoichiometry

“…Binding sites have been mapped between Stbm and Pk, as well as between Dsh and Dgo (Jenny et al., 2003, Jenny et al., 2005), and Stbm, Pk, and Dsh contain dimerization motifs (Jenny et al., 2003, Kishida et al., 1999). In addition to this, Fmi, Fz, Stbm, and Dsh contain putative PDZ (PSD-95, Discs Large, ZO-1) binding motifs of unknown function, which may interact with PDZ-containing scaffolding factors (Wolff and Rubin, 1998, Djiane et al., 2005, Wasserscheid et al., 2007, Johnston et al., 2013). Membrane interaction motifs, for example the DEP (Dishevelled, Egl10, and Pleckstrin) domain (Simons et al., 2009) and the Pk prenylation motif (Jenny et al., 2003, Lin and Gubb, 2009, Strutt et al., 2013b), may also promote association of the core proteins to junctions independently of protein-protein interaction sites.…”

The exon junction complex regulates the splicing of cell polarity gene dlg1 to control Wingless signaling in development

“…To effectively narrow down the pre-EJC targets acting in Wg signaling, we compared our candidate list with annotated information extracted from the FlyBase describing validated protein interactions with Dsh (Carmena et al, 2006; Chung et al, 2009; Kaplan and Tolwinski, 2010; Varelas et al, 2010; Johnston et al, 2013; Schertel et al, 2013; Strutt et al, 2013; Warrington et al, 2013; Garcia et al, 2014). Among 818 mRNAs whose expression was downregulated, we identified three genes, dlg1, lethal (2) giant larvae [l(2)gl ] and diablo (dbo ), whose protein products are known to directly interact with Dsh.…”

Tissue morphodynamics: Translating planar polarity cues into polarized cell behaviors

“…3A). An accessory pathway involving Dsh-mediated recruitment of Rho and Formin also promotes spindle alignment by modifying the cortical actin cytoskeleton to help anchor and position the mitotic spindle [67]. …”