Discs-Large and Strabismus are functionally linked to plasma membrane formation

Abstract

During early embryogenesis in Drosophila melanogaster, extensive vesicle transport occurs to build cell boundaries for 6,000 nuclei. Here we show that this important process depends on a functional complex formed between the tumour suppressor and adaptor protein Discs-Large (Dlg) 1 and the integral membrane protein Strabismus (Stbm)/Van Gogh (Vang) 2,3 . In support of this idea, embryos with mutations in either dlg or stbm displayed severe defects in plasma membrane formation. Conversely, overexpression of Dlg and Stbm synergistically induced excessive plasma membrane formation. In addition, ectopic co-expression of Stbm (which associated with postGolgi vesicles) and the mammalian Dlg homologue SAP97/hDlg 4,5 promoted translocation of SAP97 from the cytoplasm to both post-Golgi vesicles and the plasma membrane. This effect was dependent on the interaction between Stbm and SAP97. These findings suggest that the Dlg-Stbm complex recruits membrane-associated proteins and lipids from internal membranes to sites of new plasma membrane formation.Formation of new plasma membranes is dependent on the delivery of post-Golgi vesicles to a pre-existing plasma membrane. An excellent model system to study this process is the cellularization that occurs during early Drosophila embryogenesis. During cellularization, the embryonic plasma membrane must rapidly grow inwards to segregate thousands of nuclei, generated by synchronized cycles of nuclear division without cytokinesis, into individual cells 6 . This process occurs through addition of post-Golgi vesicles to defined regions of lengthening plasma membranes and may be required for establishing proper cell polarity 7 . The Dlg tumour suppressor is essential both for establishing proper cell polarity and for assembling multiprotein complexes at specialized cell-cell junctions 8 . Accumulating evidence also indicates that Dlg associates with its targets at intracellular membrane sites before accumulation at the plasma membrane 9-12 . The integral membrane protein Stbm, however, is a regulator of planar tissue polarity in the fly 2,3 , and mouse Loop-tail (Lp) and zebrafish trilobite mutants that also have mutations in stbm homologues display defects in gastrulation and neurogenesis 13,14 .Here,we report that Dlg binds to Stbm and that this complex is required for formation of new plasma membranes during cellularization. Note: Supplementary Information is available on the Nature Cell Biology website. COMPETING FINANCIAL INTERESTSThe authors declare that they have no competing financial interests. We identified Stbm as a binding partner of Dlg using the first and second Dlg PDZ domains (Dlg-PDZ1-2; Fig. 1a) as bait in the yeast two-hybrid system. Stbm contains four putative transmembrane domains and a consensus PDZ-domain-binding motif (PBM) at its extreme carboxyl terminus (Fig. 1a) 2 . In glutathione S -transferase (GST) pull-down assays, the 17 C-terminal residues of Stbm (GST-Stbm PBM ) were sufficient to mediate binding to Dlg-PDZ1-2 (see Supplementary Information,...

Mophogenesis and Dynamics of Post-Golgi Transport Carriers

“…In motile cells, this process is restricted to the leading edge of the cell . Visualization of exocytosis in polarized cells has revealed that the vertical growth of epithelia relies on the directed delivery of PGCs to the lateral surface of the columnar cells, where the tethering factors, such as mammalian exocyst or Drosophila DLG, reside Lee et al, 2003;. Similarly, the exocyst can define PGC docking sites in neurite growth cones of differentiating neurons (Vega and Hsu, 2001).…”

Refining the role of Lgl, Dlg and Scrib in Tumor Suppression and Beyond: Learning from the Old Time Classics

“…Rac1 is a downstream component of the Egfr pathway and acts antagonistically to Rho in order to regulate germ cell encapsulation; moreover, Rho activation perturbates TJ function in various experimental systems (Fischer et al 2007). It has already been shown that Dlg regulates membrane proliferation in a subset of NMJs in a dose-dependent fashion (Budnik et al 1996) and is an important player in the process of polarized membrane insertion during cellularization (Lecuit and Wieschaus 2000, Dudu et al 2004, Strickland and Burgess 2004, Lee et al 2003. The fact that membrane proliferation is also involved in mechanisms such as tissue spreading and cell surface extensions, including membrane ruffles (Lecuit andPilot 2003, Albertson, Riggs andSullivan 2005) and combined with our results on SCCs membrane ruffling upon Dlg overexpression, could mean that polarized membrane insertion, mediated by Dlg, might conduct SCCs growth, expansion and spreading over the germ cells of testicular cysts.…”

“…dlg, scrib and lgl are essential for planar cell polarity (PCP), by establishing a cross-talk between apical-basal and planar cell polarity. Dlg and Scrib have been shown to bind components of the core PCP machinery, including Frizzled receptors and the membrane protein Strabismus/Van Gogh (Stbm/Vang) (Montcouquiol et al 2006, Kallay et al 2006, Lee et al 2003, Hering and Sheng 2002. The direct interaction of Dlg4 with receptors of the Wnt signaling pathway, Frizzled 1-7, link mammalian Dlg to the Frizzled signaling (Humbert et al 2003, Hering andSheng 2002).…”

“…Dlg1 is also required for smooth muscle orientation in the mouse ureter (Mahoney et al 2006). In addition, Dlg binds through its PDZ1 and PDZ2 domains to Stbm/Vang in order to recruit membraneassociated proteins and lipids from internal membranes to sites of new plasma membrane formation (Lee et al 2003). In C. elegans, the unique PCP protein Vang-1 interacts with the PDZ2 domain of Dlg for its proper localization, which is required for intestinal tube formation, since in vang-1 mutant embryos the epithelial cells of the intestine are not correctly arranged along the anterior-posterior axis (Hoffmann et al 2010).…”

“…Dlg localizes to the plasma membrane along the newly formed invaginating membrane, whereas Stbm/Vang is localized initially to the Golgi. Both Stbm/Vang and Dlg are required for membrane deposition during cellularization and their simultaneous overexpression induces expansion of the lateral membrane (Lee et al 2003). In the membrane-recycling pathway, the apical membrane is internalized through a Dynamindependent process, travels through the Rab5 early endosome and Rab11 recycling endosome acting together with Nuf, and finally becomes exocytosed at the lateral membrane (Dudu et al 2004, Strickland and Burgess 2004, Pelissier, Chauvin and Lecuit 2003, Riggs et al 2003, Lecuit 2004).…”