Overexpression of XMyoD or XMyf5 in Xenopus Embryos Induces the Formation of Enlarged Myotomes through Recruitment of Cells of Nonsomitic Lineage

[摘要] Themyogenicregulatoryfactors(MRFs)MyoDandMyf5aretheearliestdescribedmuscle-specificgenestobeexpressedinXenopusdevelopment.TostudytheinvivoeffectsofoverexpressingXenopusMyoDandMyf5,syntheticRNAsweremicroinjectedintosingleblastomeresof2-to32-cellstageXenopusembryos.InvivooverexpressionoftheseMRFsinitiatestheprecociousandectopicexpressionofactinandmyosin.TheeffectsofunilateralinjectionofeithermRNAwereindistinguishable;embryosinjectedatthe2-cellstageshowedipsilaterallyenlargedcranialandanteriortrunkmyotomescomposedofincreasednumbersofprimarymyotomemyocytes.Inaddition,formationofectopicmuscleinlateralplateandneuraltissuewasobserved.TheMRF-inducedeffectspersistthroughsecondarymyogenesis,withtheenlargedcranialmyotomesfailingtoundergothenormalprogramofdegeneration.ExperimentscombiningMRFRNAandlineagetracerinjectionsshowedthatmyotomalenlargementisdueinparttothecontributionofcellsofnonsomiticlineagetothemyotome,ratherthantoanincreaseinmuscleprecursorcelldivision.OverexpressionofXMyoDendXMyf5alsoaffectedthemorphogenesisoftheskinandthenervoussystem.TheseresultsrevealthatoverexpressionofXMyoDorXMyf5invivoclearlyinfluencestheregulationofearlymyogenesisandthemorphogenesisofskinandnervoustissue.