RhoE controls myoblast alignment prior fusion through RhoA and ROCK.
Differentiation of skeletal myoblasts into multinucleated myotubes is a multi-step process orchestrated by several signaling pathways. The Rho small G protein family plays critical roles both during myogenesis induction and myoblast fusion. We report here that in C2C12 myoblasts, expression of RhoE, an atypical member of this family, increases until the onset of myoblast fusion before resuming its basal level once fusion has occurred. We show that RhoE accumulates in elongated, aligned myoblasts prior to fusion and that its expression is also increased during injury-induced skeletal muscle regeneration. Moreover, although RhoE is not required for myogenesis induction, it is essential for myoblast elongation and alignment before fusion and for M-cadherin expression and accumulation at the cell-cell contact sites. Myoblasts lacking RhoE present with defective p190RhoGAP activation and RhoA inhibition at the onset of myoblast fusion. RhoE interacts also with the RhoA effector Rho-associated kinase (ROCK)I whose activity must be downregulated to allow myoblast fusion. Consistently, we show that pharmacological inactivation of RhoA or ROCK restores myoblast fusion in RhoE-deficient myoblasts. RhoE physiological upregulation before myoblast fusion is responsible for the decrease in RhoA and ROCKI activities, which are required for the fusion process. Therefore, we conclude that RhoE is an essential regulator of myoblast fusion.
Fortier
M
M
Universités Montpellier 2 et 1, CRBM, CNRS, UMR 5237, IFR 122 1919 Route de Mende, 34293 Montpellier, France.
Comunale
F
F
Kucharczak
J
J
Blangy
A
A
Charrasse
S
S
Gauthier-Rouvière
C
C
D000818:Animals; D002454:Cell Differentiation; D002459:Cell Fusion; D002460:Cell Line; D048430:Cell Shape; D015536:Down-Regulation; D020690:GTPase-Activating Proteins / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008855:Microscopy, Electron, Scanning; D018485:Muscle Fibers, Skeletal / Q000166:cytology; D032446:Myoblasts / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D015398:Signal Transduction; D015854:Up-Regulation; D020741:rho GTP-Binding Proteins / Q000378:metabolism*; D054460:rho-Associated Kinases / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000378:metabolism*
D020690:GTPase-Activating Proteins; C085379:rho GTPase-activating protein; D054460:rho-Associated Kinases; C513341:Rnd3 protein, mouse; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein