isaneconomicallyimportantbreedingcrabfoundalongthesoutheastcoastofChina.Althoughextensiveresearchonreproductivephysiologyhasbeencarriedoutforthisspecies,descriptionoftheregulatorymechanismofthegonaddevelopmentatamolecularlevelislimited.Withinalltissues,themajorityofintracellularproteinsaredegradedbytheubiquitin(Ub)–proteasomepathway(UPP).Inthispathway,UbisconjugatedtoproteinsthataredestinedfordegradationbyanATP-dependentprocessthatinvolvesthreeenzymes.Todate,somestudieshavediscoveredthatcomponentsoftheubiquitinsystemmaybeinvolvedinvariousstepsandprocessesduringgametogenesis,modulationofsteroidreceptorconcentrations,placentaldevelopmentandendometrialmodificationatthebeginningofpregnancy.However,researchontheactionofUPPingonaddevelopmentincrabspeciesUbgene()wasidentifiedandcharacterizedusinganapproachwhichcombinestheexpressedsequencetag(EST)methodandrapidamplificationofcDNAend(RACE).Theexpressionprofileofinthevarioustissuesanddifferentdevelopingstagesofthegonadwasdeterminedbyreal-timequantitativePCR.ThefulllengthcDNAofthegeneisof555bp.Itencodesaproteinof154aminoacids,inwhichthe1-76aminoacidsfallwithintheubiquitindomain,andthe101147aminoacidsfallwithintheribosomal_S27adomain.ThesecondstructurepredictionrevealedthattheubiquitindomainoftheSp-Ubproteincontainsfiveextendedstrands,anα-helixandsomerandomcoils.Moreover,thethree-dimensionalstructurepredictedbytheSWISS-MODELshowedthatitcontainsanα-helixandfourβ-pleatedsheets.AlignmentoftheaminoacidsequenceswithindifferentUbproteinsindicatedthattheubiquitindomainandtheribosomal_S27adomainamongdifferentspeciesarehighlyconservedduring.Real-timequantitativePCRresultsshowedthatwasexpressedbytheubiquitindomaininalltissuesexamined(P>0.05)whichillustratedthattheUbgeneplaysawidevarietyofrolesinbiologicalprocesses.TheexpressionprofilesofinthedifferentdevelopingstagesoftheovaryrevealedthatitsexpressionlevelwasthehighestatstageO5followingstageO1,O4andO3.ItwasthelowestlevelatstageO2whichwassignificantlylowerthanstageO5(P<0.05).Withinthedevelopingstagesofthetestis,theexpressionlevelofwashigherinstageT2followingstageT1andT3,anditsexpressionlevelwassignificantlyhigherinstageT2comparedtostageT3(P<0.05).Duringgametogenesis,theoogoniaandspermatogoniumundergoactivemitosisproliferationforincreasingtheirnumberattheproliferationstage.Previousresearchshowedthatcyclin/Cdksworkcloselywiththeubiquitin-proteasomepathwayduringthemitoticcycle.Thus,itisreasonabletoobservethattheexpressionlevelofexpressionlevelatstageO2maybeduetotheinitiationofformationofprimaryoocytes,andinitialvitellogenesiswithalowlevelofproliferation.Moreover,theexpressionlevelofgraduallyincreasedastheyolkproteinswereaccumulatinginthegrowingoocytesduringvitellogenesis.Amassofproteinsneededtobesynthesizedanddegradedduringgametogenesis,andtheevidenceofubiquitin–conjugatedvitellinpolypeptidesininsectoocyteshadbeenreported.Theseresultsindicatedthatmaybeinvolvedinvitellogenesis.Furthermore,thetestisofcrabcontainsgermcellsofvariousdevelopmentstageswithintheseminiferoustubules.Hence,thehigherexpressionlevelofdevelopmentmaybenecessaryforfastincreasingthenumberofspermatocytecells,whichindicatedthatUPPwasmoreactiveinthesecells.Conclusively,ourstudiesarethefirstreportofcloningandexpressionprofilingofUbincrustaceans.AlloftheseresultscanprovidebasicdatashowingtheroleofSp-Ubwithinthegonaddevelopmentofthecrab.