title: GRAF1 promotes ferlin-dependent myoblast fusion.
abstract: Myoblast fusion (a critical process by which muscles grow) occurs in a multi-step fashion that requires actin and membrane remodeling; but important questions remain regarding the spatial/temporal regulation of and interrelationship between these processes. We recently reported that the Rho-GAP, GRAF1, was particularly abundant in muscles undergoing fusion to form multinucleated fibers and that enforced expression of GRAF1 in cultured myoblasts induced robust fusion by a process that required GAP-dependent actin remodeling and BAR domain-dependent membrane sculpting. Herein we developed a novel line of GRAF1-deficient mice to explore a role for this protein in the formation/maturation of myotubes in vivo. Post-natal muscles from GRAF1-depleted mice exhibited a significant and persistent reduction in cross-sectional area, impaired regenerative capacity and a significant decrease in force production indicative of lack of efficient myoblast fusion. A significant fusion defect was recapitulated in isolated myoblasts depleted of GRAF1 or its closely related family member GRAF2. Mechanistically, we show that GRAF1 and 2 facilitate myoblast fusion, at least in part, by promoting vesicle-mediated translocation of fusogenic ferlin proteins to the plasma membrane.
authors.affiliation: Department of Pathology and Laboratory, Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA.
authors.forename: Kaitlin C
authors.initials: KC
authors.lastname: Lenhart
authors.affiliation: Department of Pathology and Laboratory, Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA.
authors.forename: Abby L
authors.initials: AL
authors.lastname: Becherer
authors.affiliation: Department of Gene Therapy Molecular Pharmaceutics, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA.
authors.forename: Jianbin
authors.initials: J
authors.lastname: Li
authors.affiliation: Department of Gene Therapy Molecular Pharmaceutics, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA.
authors.forename: Xiao
authors.initials: X
authors.lastname: Xiao
authors.affiliation: Department of Medicine, The University of Chicago, Chicago, IL, USA.
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: McNally
authors.affiliation: Department of Pathology and Laboratory, Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA; McAllister Heart Institute, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Mack
authors.affiliation: Department of Pathology and Laboratory, Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599, USA; McAllister Heart Institute, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA. Electronic address: jmt3x@med.unc.edu.
authors.forename: Joan M
authors.initials: JM
authors.lastname: Taylor
mesh_terms: D000818:Animals; D001692:Biological Transport; D020126:Brefeldin A / Q000494:pharmacology; D002459:Cell Fusion; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D020690:GTPase-Activating Proteins / Q000235:genetics*; D006056:Golgi Apparatus / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D024510:Muscle Development / Q000235:genetics*; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D009124:Muscle Proteins / Q000378:metabolism*; D032446:Myoblasts / Q000378:metabolism*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D034622:RNA Interference; D034741:RNA, Small Interfering; D033921:Vesicular Transport Proteins
chemical_list: C485640:Ehd1 protein, mouse; C557795:FER1L5 protein, mouse; C000593136:GRAF1 protein, mouse; D020690:GTPase-Activating Proteins; D008565:Membrane Proteins; D009124:Muscle Proteins; D011500:Protein Synthesis Inhibitors; D034741:RNA, Small Interfering; D033921:Vesicular Transport Proteins; C521810:myoferlin protein, mouse; D020126:Brefeldin A
keywords: Endocytic recycling; Ferlin; GRAF; Myoblast fusion