title: The SCAR and WASp nucleation-promoting factors act sequentially to mediate Drosophila myoblast fusion.
abstract: The actin nucleation-promoting factors SCAR/WAVE and WASp, together with associated elements, mediate the formation of muscle fibres through myoblast fusion during Drosophila embryogenesis. Our phenotypic analysis, following the disruption of these two pathways, suggests that they function in a sequential manner. Suppressor of cyclic AMP receptor (SCAR) activity is required before the formation of pores in the membranes of fusing cells, whereas Wiskott-Aldrich syndrome protein (WASp) promotes the expansion of nascent pores and completion of the fusion process. Genetic epistasis experiments are consistent with this step-wise temporal progression. Our observations further imply a separate, Rac-dependent role for the SCAR complex in promoting myoblast migration. In keeping with the sequential utilization of the two systems, we observe abnormal accumulations of filamentous actin at the fusion sites when both pathways are disrupted, resembling those present when only SCAR-complex function is impaired. This observation further suggests that actin-filament accumulation at the fusion sites might not depend on Arp2/3 activity altogether.
authors: Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel.
authors: Boaz
authors: B
authors: Gildor
authors: R'ada
authors: R
authors: Massarwa
authors: Ben-Zion
authors: BZ
authors: Shilo
authors: Eyal D
authors: ED
authors: Schejter
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D002459:Cell Fusion; D002465:Cell Movement; D002467:Cell Nucleus / Q000378:metabolism*; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000166:cytology* / Q000196:embryology / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism*; D008854:Microscopy, Electron; D032446:Myoblasts / Q000166:cytology* / Q000378:metabolism*; D010641:Phenotype; D051316:Wiskott-Aldrich Syndrome Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D000199:Actins; D029721:Drosophila Proteins; D008840:Microfilament Proteins; C449671:SCAR protein, Drosophila; C477859:WASp protein, Drosophila; D051316:Wiskott-Aldrich Syndrome Protein