title: The Formin Diaphanous Regulates Myoblast Fusion through Actin Polymerization and Arp2/3 Regulation.
abstract: The formation of multinucleated muscle cells through cell-cell fusion is a conserved process from fruit flies to humans. Numerous studies have shown the importance of Arp2/3, its regulators, and branched actin for the formation of an actin structure, the F-actin focus, at the fusion site. This F-actin focus forms the core of an invasive podosome-like structure that is required for myoblast fusion. In this study, we find that the formin Diaphanous (Dia), which nucleates and facilitates the elongation of actin filaments, is essential for Drosophila myoblast fusion. Following cell recognition and adhesion, Dia is enriched at the myoblast fusion site, concomitant with, and having the same dynamics as, the F-actin focus. Through analysis of Dia loss-of-function conditions using mutant alleles but particularly a dominant negative Dia transgene, we demonstrate that reduction in Dia activity in myoblasts leads to a fusion block. Significantly, no actin focus is detected, and neither branched actin regulators, SCAR or WASp, accumulate at the fusion site when Dia levels are reduced. Expression of constitutively active Dia also causes a fusion block that is associated with an increase in highly dynamic filopodia, altered actin turnover rates and F-actin distribution, and mislocalization of SCAR and WASp at the fusion site. Together our data indicate that Dia plays two roles during invasive podosome formation at the fusion site: it dictates the level of linear F-actin polymerization, and it is required for appropriate branched actin polymerization via localization of SCAR and WASp. These studies provide new insight to the mechanisms of cell-cell fusion, the relationship between different regulators of actin polymerization, and invasive podosome formation that occurs in normal development and in disease.
authors: Graduate Program in Physiology, Biophysics & Systems Biology, Weill Cornell Graduate School of Medical Sciences, Cornell University, New York, New York, United States of America.
authors: Su
authors: S
authors: Deng
authors: Program in Developmental Biology, Sloan Kettering Institute, New York, New York, United States of America.
authors: Ingo
authors: I
authors: Bothe
authors: Graduate Program in Physiology, Biophysics & Systems Biology, Weill Cornell Graduate School of Medical Sciences, Cornell University, New York, New York, United States of America; Program in Developmental Biology, Sloan Kettering Institute, New York, New York, United States of America.
authors: Mary K
authors: MK
authors: Baylies
mesh_terms: D051376:Actin-Related Protein 2-3 Complex / Q000378:metabolism*; D000199:Actins / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000502:physiology*; D002459:Cell Fusion; D002460:Cell Line; D029721:Drosophila Proteins / Q000378:metabolism / Q000502:physiology*; D004331:Drosophila melanogaster / Q000166:cytology / Q000502:physiology*; D005260:Female; D000080865:Formins; D008297:Male; D008840:Microfilament Proteins / Q000378:metabolism; D024510:Muscle Development; D032446:Myoblasts; D000069261:Podosomes / Q000378:metabolism; D055503:Protein Multimerization; D021381:Protein Transport; D051316:Wiskott-Aldrich Syndrome Protein / Q000378:metabolism
chemical_list: D051376:Actin-Related Protein 2-3 Complex; D000199:Actins; D002352:Carrier Proteins; D029721:Drosophila Proteins; D000080865:Formins; D008840:Microfilament Proteins; C449671:SCAR protein, Drosophila; C477859:WASp protein, Drosophila; D051316:Wiskott-Aldrich Syndrome Protein; C106890:diaphanous protein, Drosophila