VectorBuilder’sshRNATargetDesigntoolallowsyoutodesignshorthairpinRNAs(shRNAs)withhighknockdownscorestohelpyouachievehighlyefficientknockdownofyourgenesofinterest(GOIs).
VectorBuilderappliesrulessimilartothoseusedbytheRNAiconsortium(TRC)todesignandscoreshRNAs.ForeachgivenRefSeqtranscript,wesearchforallpossible21mersthatareconsideredascandidatetargetsites.Candidatesareexcludediftheycontainfeaturesthoughttoreduceknockdownefficiency/specificityorclonability,includingarunof≥4ofthesamebase,arunof≥7GorC,GCcontent<25%or>60%,andAAatthe5’end.Knockdownscoresarepenalizedforcandidatesthatcontaininternalstem-loop,highGCcontenttowardthe3’end,knownmiRNAseedsequences,oroff-targetmatchestoothergenes.Forgeneswithalternativetranscripts,targetsitesthatexistinalltranscriptsaregivenhigherscores.
Allscoresare≥0,withmeanat~5,standarddeviationat~5,and95%ofscores≤15.AnshRNAwithaknockdownscoreabout15isconsideredtohavethebestknockdownperformanceandclonability,whileanshRNAwithaknockdownscoreof0hastheworstknockdownperformanceorishardtobecloned.
RNAinterference(RNAi)hasbeenawidelyutilizedmethodofgenemodulationformanydecades.ShortRNAsequences(approximately21-23nucleotides)complementarytotheRNAofageneofinterestareintroducedintotargetcells.TheexogenousRNAstrandbindstothecomplementaryendogenousmRNAstrand.Thecelldegradesthedouble-strandedRNAandtranslationdoesnotoccur,knockingdowntheperformanceofthegene.Itisimportanttonotethatthisapproachdoesnotcompletelyknockoutthegene,assomemRNAswillnotbeboundandwillproducefunctionalprotein.
OnecommonRNAiapproachutilizesshorthairpinRNAs(shRNAs).Herethesequenceisdesignedsuchthatasingletranscriptfoldsbackonitselfandhybridizes,formingahairpin.Thisdouble-strandedRNAcomplexwithitsinternalloopistransportedintothecytoplasm,whereitisprocessedbyDicerandisloadedintotheRISCcomplex.TheRISCcomplexfacilitatesbindingbetweenthesilencingRNAandthetargetmRNA,atwhichpointthemRNAwillbecleavedordegraded(Figure1).
Figure1.ProductionandfunctionofformsofRNAi.
Theformationofahairpinfromasingletranscriptallowsforcustomizationinintroduction,duration,andregulationofsilencing.TheplasmidcodingfortheshRNAcanbetransfected(e.g.throughelectroporationormicroinjection)ortransduced(usingvirusessuchaslentivirusoradenovirus).Becauseoftheoptiontouseviraltransduction,shRNAvectorscanbetaggedand/orintegratedintothegenomeusingvirusmachineryandcanbeintroducedtoawiderangeofcelltypes.