HEARTDEVELOPMENTDefiningtheearlieststepofcardiovascularlineagesegregationbysingle-cellRNA-seqFabienneLescroart,1*XiaonanWang,2,3*XionghuiLin,1*BenjaminSwedlund,1SouhirGargouri,1AdrianaSànchez-Dànes,1VictoriaMoignard,2,3ChristineDubois,1CatherinePaulissen,1SarahKinston,2,3BertholdGöttgens,2,3†‡CédricBlanpain1,4†‡MouseheartdevelopmentarisesfromMesp1-expressingcardiovascularprogenitors(CPs)thatarespecifiedduringgastrulation.ThemolecularprocessesthatcontrolearlyregionalandlineagesegregationofCPshavebeenunclear.Weperformedsingle-cellRNAsequencingofwild-typeandMesp1-nullCPsinmice.WeshowedthatpopulationsofMesp1CPsaremolecularlydistinctandspanthecontinuumbetweenepiblastandlatermesodermalcells,includinghematopoieticprogenitors.Single-celltranscriptomeanalysisofMesp1-deficientCPsshowedthatMesp1isrequiredfortheexitfromthepluripotentstateandtheinductionofthecardiovasculargeneexpressionprogram.WeidentifieddistinctpopulationsofMesp1CPsthatcorrespondtoprogenitorscommittedtodifferentcelllineagesandregionsoftheheart,identifyingthemolecularfeaturesassociatedwithearlylineagerestrictionandregionalsegregationoftheheartattheearlystageofmousegastrulation.Themammalianheartiscomposedofdif-ferentregions(ventricles,atria,andgreatvessels)andcelltypes,includingcardio-myocytes(CMs),endocardialcells(ECs),smoothmusclecells(SMCs),andepicar-dialcells(EPs)(1).Heartdevelopmentbeginsatgastrulation,duringwhichCPsleavetheprim-itivestreak(PS)andmigratetowardtheantero-lateralpoleoftheembryo(2).Fromembryonicday6.25(E6.25)toE7.25,Mesp1markstheearlyCPswithinthePS,whereasadaylater,Mesp1isexpressedinthesomites(2,3).Mesp1+cellsgiverisetoallheartcells,ECsoftheaortaandbrain,somemusclesoftheheadandneck,aswellastofewsomiticderivativesandlivercellsfromitslaterexpression(2,4–6).TemporallyinducibleMesp1lineagetracingshowsthatatE6.5,Mesp1+cellsmarkleftventricle(LV)progenitors,where-astherightventricle,atria,outflow,andinflowtractsandheadmusclesarisefromMesp1+cellsatE7.25,whichcorrespondrespectivelytothefirst...
