title: A dual role of the GTPase Rac in cardiac differentiation of stem cells.
abstract: The function of the GTPase Rac1, a molecular switch transducing intracellular signals from growth factors, in differentiation of a specific cell type during early embryogenesis has not been investigated. To address the question, we used embryonic stem (ES) cells differentiated into cardiomyocytes, a model that faithfully recapitulates early stages of cardiogenesis. Overexpression in ES cells of a constitutively active Rac (RacV12) but not of an active mutant (RacL61D38), which does not activate the NADPH oxydase generating ROS, prevented MEF2C expression and severely compromised cardiac cell differentiation. This resulted in poor expression of ventricular myosin light chain 2 (MLC2v) and its lack of insertion into sarcomeres. Thus ES-derived cardiomyocytes featured impaired myofibrillogenesis and contractility. Overexpression of MEF2C or addition of catalase in the culture medium rescued the phenotype of racV12 cells. In contrast, RacV12 specifically expressed in ES-derived ventricular cells improved the propensity of cardioblasts to differentiate into beating cardiomyocytes. This was attributed to both a facilitation of myofibrillogenesis and a prolongation in their proliferation. The dominant negative mutant RacN17 early or lately expressed in ES-derived cells prevented myofibrillogenesis and in turn beating of cardiomyocytes. We thus suggest a stage-dependent function of the GTPase during early embryogenesis.
authors.affiliation: Centre de Recherches de Biochimie Macromoléculaire, CNRS FRE 2593, IFR24, Montpellier, France. puceat@crbm.cnrs-mop.fr
authors.forename: Michel
authors.initials: M
authors.lastname: Pucéat
authors.forename: Pierre
authors.initials: P
authors.lastname: Travo
authors.forename: Mark T
authors.initials: MT
authors.lastname: Quinn
authors.forename: Philipe
authors.initials: P
authors.lastname: Fort
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000502:physiology*; D002478:Cells, Cultured; D015536:Down-Regulation; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D006321:Heart / Q000196:embryology*; D064326:MEF2 Transcription Factors; D051379:Mice; D024510:Muscle Development / Q000235:genetics / Q000502:physiology; D009154:Mutation; D032383:Myocytes, Cardiac / Q000166:cytology / Q000378:metabolism*; D018006:Myogenic Regulatory Factors / Q000378:metabolism; D018994:Myosin Light Chains / Q000096:biosynthesis; D019255:NADPH Oxidases / Q000378:metabolism; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism; D012518:Sarcomeres / Q000378:metabolism; D013234:Stem Cells / Q000166:cytology* / Q000378:metabolism; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D064326:MEF2 Transcription Factors; C578041:Mef2c protein, mouse; D018006:Myogenic Regulatory Factors; D018994:Myosin Light Chains; D017382:Reactive Oxygen Species; D019255:NADPH Oxidases; D020830:rac1 GTP-Binding Protein