简介：Peptidenucleicacids(PNAs)aresyntheticoligonucleotideswithchemicallymodifiedbackbones.PNAscanbindtobothDNAandRNAtargetsinasequence-specificmannertoformPNA/DNAandPNA/RNAduplexstructures.Whenboundtodouble-strandedDNA(dsDNA)targets,thePNAmoleculereplacesoneDNAstrandintheduplexbystrandinvasiontoformaPNA/DNA/PNA[or(PNA)2/DNA]triplexstructureandthedisplacedDNAstrandexistsasasinglestrandedD-loop.PNAhasbeenusedinmanystudiesasresearchtoolsforgeneregulationandgenetargeting.TheDloopsgeneratedfromthePNAbindinghavealsobeendemonstratedforitspotentialininitiatingtranscriptionandinducinggeneexpression.PNAprovidesapowerfultooltostudythemechanismoftranscriptionandaninnovativestrategytoregulatetargetgeneexpression.AnunderstandingofthePNA-mediatedgeneregulationwillhaveimportantclinicalimplicationsintreatmentofmanyhumandiseasesincludinggenetic,cancerous,andage-relateddiseases.

简介：ThemuscleproteinmyosinbindingproteinC(MyBPC)isalargemulti-domainproteinwhoseroleinthesarcomereiscomplexandnotyetfullyunderstood.MutationsinMyBPCarestronglyassociatedwiththeheartdiseasefamilialhypertrophiccardiomyopathy(FHC)andtheseexperimentsofnaturehaveprovidedsomeinsightintotheintricateworkingsofthisproteinintheheart.WhilesomeregionsoftheMyBPCmoleculehavebeenassignedafunctionintheregulationofmusclecontraction,theinteractionofotherregionswithvariouspartsofthemyosinmoleculeandthesarcomericproteins,actinandtitin,remainobscure.Inadditicn,severalintra-domaininteractionsbetweenadjacentMyBPCmoleculeshavebeenidentified.Althoughthebasicstructureofthemolecule(aseriesofimmunoglobulinandfibronectindomains)hasbeenelucidated,theassemblyofMyBPCinthesarcomereisatopicfordebate.ByanalysingtheMyBPCsequencewithrespecttoFHC-causingmutationsitispossibletoidentifyindividualresiduesorregionsofeachdomainthatmaybeimportanteitherforbindingorregulation.Thisreviewlooksatthecurrentliterature,inconcertwithalignmentsandthestructuralmodelsofMyBPC,inanattempttounderstandhowFHCmutationsmayleadtothediseasestate.

简介：TheundecapeptidesubstanceP(SP)wasshowntobeintimatelyinvolvedinboththestructuralandfunctionalaspectsoftheanteriorpituitary.Yet,inadditiontoitsinfluencesonhormonalsecretion,SPmaywellpossessmoreactionsinthismastergland.ThepresentstudywasfthereforeaimedtoinvestigatetheeffectofSPontheproliferationofratanteriorpituitarycellsinprimaryculture,ItwasfoundthatSPcoulddose-dependentlyincreasetheincorporationoftritiatedthymidine(3H-TdR)intoculturedanteriorpituitarycells.OthermammaliantachykininssuchasneurokininAandneurokininBhadsimilareffectbuttovaryingdegrees.TheequipotentanalogueofSP,Norleucine^11-SP(Nle^11-SP),alsoactedlikewise.withitsactionantagonizablebyspantide,aSPreceptorblocker.TofurthercharacterizethenatureofcellsresponsivetothechallengeofSP,immunocytochemicalstainingagainstS-100proteinandsomeadenohypophysealhormoneswasperformedaloneorplusautoradiography.TheresultsshowedthatthepercentageofS-100proteinimmunorectivecellswasapparentlyelevatedbytheaddtionofNle^11-Spfor48h,whichindicatesapreferentialproliferationoffolliculo-stellatecellsundertheregime.ThiswasconfirmedbyincreasesinimmunocytochemicalorautoradiographicallabellingindicesofanteriorpituitarySubstancePandanteriorpituitarycellproliferation.Cellstreatedsimilarly.Takentogether,TheseresultsrevealthatthetrophicactionofSPobservedpreviouslyinothertissuesisalsopresentatleastinculturedratanteriorpituitarycells.withrespondingcellsbeingpredominantlyfolliculo-stellatecellsastypifiedbyS-100proteinimmunoreactivity.Therefore,anintra-pituitarytrophicactionofSPinvivocouldbeanticipated.

简介：Coactivatorsandcorepressorsregulatetranscriptionbycontrollinginteractionsbetweensequence-specifictranscriptionfactors,thebasaltranscriptionalmachineryandthechromatinenvironment,Thisreviewconsidertheaccessofnuclearandsteroidreceptorstochromatin,theiruseofcorepressorsandcoactivatorstomodifychromatinstructureandtheimplicationsfortranscriptionalcontrol.Theassemblyofspecificnucleoproteinarchitecturesandtargetedhistonemodificationemergeascentralcontrollingelementsforgeneexpression.

简介：<正>Usingsubtractioncloning,weidentifiedthehumanN-MycDownstream-RegulatedGene-2(hNDRG2),locatedat14q11.2,asacandidatetumorsuppressorgene.Semi-quantitativeRT-PCRshowedthattheexpressionofhNDRG2in15of27(56%)humanGBMtissuesandall6humanglioblastomacelllineswassignificantlylowerthanthatinthenormalbrain.TheexpressionofhNDRG2alsowasevaluatedin60lung-carcinomapatients.17of26casesofsquamouscarcinomaand4of11casesofsmallcelllungcancerdisplayed

简介：P28，a28kDproteinfromtoad(Bufobufogargarizans)oocytes,wasidentifiedbyusingP13^suc1-agaroseaffinitychromatography.Sequencehomologyanalysisofthefull-lengthcDNAofP28(GeneBankaccessionnumber:AF314091)indicatedthatitencodesaproteincontaining224amino-acidswithabout55%iden-titiesandmorethan70%positivestoencodesaproteincontaining224amino-acidswithabout55%iden-titiesandmorethan70%positivestohuman,ratormouseUCH-L1,andcontainshomologicalfunctionaldomainsofUCHfamily.Anti-p28monoclonalantibody,oninjectingintotheoocytes,couldinhibittheprogesterone-inducedresumptionofmeioticdivisioninadose-dependentmanner.TherecombinantproteinP28showedsimilarSDS/PAGEbehaviorstothenativeone,andpromotedubiquitinethylesterhydrolysis,aclassicalcatalyticreactionforubiquitincarboxylterminalhydrolases(UCHs).Theresultsinthispaperrevealthatanovelprotein,p28,existsinthetoadoocytes,isaUCHLlhomolog,wasengagedintheprocessofprogesterone-inducedoocytematurationpossiblythroughaninvolvementinproteinturnoveranddegradation.

简介：cAMPmediatedsignalingmayplayasuppressiveroleinimmuneresponse.WepreviouslyfoundthatthecAMP-elevators(CTxand8-Br-cAMP)inhibitedIL-12,IL-la,IL-6geneexpression,butincreasedthetranscriptionallevelsofIL-10andIL-1RainLPS-treatedmurineperitonealmacrophages.ThepresentstudyexaminedapossiblemolecularmechanisminvolvedincAMPelevators-inducedinhibitionofIL-12p40expressioninresponsetoLPS.OurdatademonstratedthatcAMPelevatorsdownregulatedIL-12p40mRNAexpressionandIL-12pT0productioninmurineperitonealmacrophages.SubsequentstudiesrevealedthatcAMP-elevatorsblockedphosphorylationofp38MAPK,butdidnotaffecttheactivityofNF-κBbindingtoIL-12promoter(-136/-112).ThisisthefirstreportthatcAMPelevatorsinhibitLPS-inducedIL-12productionbyamechanismthatisassociated,atleastinpart,withp38-dependentinhibitionbycAMPsignalingpathways.

简介：ToexplorethemolecularmechanismofchromatinremodelinginvolvedintheregulationoftranscriptionalactivationofspecificgenesbyamyogenicregulatoryfactorMyogenin,weusedNIH3T3fibroblastswithastablyintegratedH1.1-GFPfusionproteintomonitorhistoneH1movementdirectlybyfluorescencerecov-eryafterphotobleaching(FRAP)inlivingcells.TheobservationfromFRAPexperimentswithmyogenintransfectedfibroblastsshowedthattheexchangerateofhistoneH1inchromatinwasobviouslyincreased,indicatingthatforcedexpressionofexogenousMyogenincaninducechromatinremodeling.Thehyper-acetylationofhistonesH3andH4frommyogenintransfectedfibroblastswasdetectedbytriton-acid-urea(TAU)/SDS(2-D)electrophoresisandWesternblotwithspecificantibodiesagainstacetylatedN-terminiofhistonesH3andH4.RT-PCRanalysisindicatedthatthenAChRa-subunitgenewasexpressedinthetrans-fectedfibroblasts.TheseresultssuggestthattheexpressionofexogenousMyogenincaninducechromatinremodelingandactivatethetranscriotionofMvogenin-targetedgeneinnon-musclecells.

简介：Thehyperpolarization-activatedcurrent(If)playsanimportantroleindeterminingthespontaneousrateofcardiacpacemakercells.Theautomaticrhythmicityalsoexistsinworkingcellsofembryonicheart,thereforewestudieddevelopmentalchangesinfunctionalexpressionandβ-adrenergicregulationofIfinembryonicmouseheart.TheexpressionofIfishighinearlydevelopmentalstage(EDS)(10.5daftercoitus)ventricularmyocytes,lowinintermediatedevelopmentalstage(IDS)(13.5d)atrialorventricularmyocytesandevenlowerinlatedevelopmentalstage(LDS)(16.5d)atrialorventricularmyocytes,indicatingthatthesecellsoftheEDSembryonichearthavesomepropertiesofpacemakercells.β-adrenergicagonistisoproterenol(ISO)stimulatesIfinLDSbutnotinEDScardiomyocytes,indicatingthattheβ-adrenergicregulationofIfisnotmatureinEDSembryonicheart.Butforskolin(adirectactivatorofadenylatecyclase)and8-Br-cAMP(amembrane-permeableanalogueofcAMP)increasetheamplitudeofIfinEDScells,indicatingthatadenylatecyclaseandcAMPfunctionfairlywellatearlystageofdevelopment.Furthermore,theresultsdemonstratethatIfismodulatedbyphosphorylationviacAMPdependentPKAbothinEDSandLDScells.

简介：Expressionoftheadhesionmolecules,ICAM-1,VCAM-1,NCAM,CD44,CD49d(VLA-4,αchain),andCDlla(LFA-1,αchain)onmouseoocytes,andpre-andperi-implantationstageembryoswasexam-inedbyquantitativeindirectimmunoliuorescencemicroscopy.ICAM-1wasmoststronglyexpressedattheoocytestage,graduallydecliningalmosttoundetectablelevelsbytheexpandedblastocyststage.NCAM,alsoexpressedmaximallyontheoocyte,declinedtoundetectablelevelsbeyondthemorulastage.Ontheotherhand,CD44declinedfromhighestexpressionattheoocytestagetoshowasecondmaximumatthecompacted8-cell/morula.Thismoleculeexhibitedhighexpressionaroundcontactareasbetweentrophecto-dermandzonapellucidaduringblastocysthatching.CD49dwashighlyexpressedintheoocyte,remainedsignificantlyexpressedthroughoutandafterblastocysthatchingwasexpressedonthepolartrophecto-derm.LikeCD44,CD49ddeclinedtoundetectablelevelsattheblastocystoutgrowthstage.ExpressionofbothVCAM-1andCDllawasundetectablethroughout.ThediametricaltemporalexpressionpatternofICAM-1andNCAMcomparedtoCD44andCD49dsuggestthatdynamicchangesinexpressionofadhesionmoleculesmaybeimportantforinteractionoftheembryowiththematernalcellularenvironmentaswellasforcontinuingdevelopmentandsurvivaloftheearlyembryo.

简介：IL-16isaligandandchemotacticfactorforCD4+Tcells.IL-16inhibitstheCD3mediatedlymphocyteactivationandproliferation.TheeffectsofIL-16onthetargetcellsaredependentonthecelltype,thepresenceofco-activatorsetc.TounderstandtheregulationfunctionandmechanismofIL-16ontargetcells,weuseda130a.a.recombinantIL-16tostudyitseffectsonthegrowthofJurkatTleukemiacellsinvitro.WefoundthattherIL-16stimulatedtheproliferationofJurkatcellsatlowdose(10^-9M),butinhibitedthegrowthofthecellsathigherconcentration(10^-5M).Resultsshowedthat10^-5MofrIL-16treatmentinducedanenhancedapoptosisinJurkatcells.ThetreatmentblockedtheexpressionofFasL,butup-regulatedthec-mycandBidexpressioninthecells.Pre-treatmentofPKCinhibitororMEK1inhibitormarkedlyincreasedordecreasedtherIL-16inducedgrowth-inhibitingeffectsonJurkatcells,respectively.TheresultssuggestedthattherIL-16mightbearegulatorforthegrowthorapoptosisofJurkatcellsatadose-dependentmanner.Thegrowth-inhibitingeffectsofrIL-16mightbeFas/FasLindependent,but,associatedwiththeactivationofPKC,up-regulatedexpressionofc-MycandBid,andtheparticipationoftheERKsignalpathwayinJurkatcells.

简介：Mammaliancelltotipotencyisasubjectthathasfascinatedscientistsforgenerations.AlonglastingquestionwhethersomeofthesomaticcellsretainstotipotencywasansweredbythecloningofDollyattheendofthe20thcentury.Thedawnofthe218thasbroughtforwardgreatexpectationsinharnessingthepoweroftotipotentcyinmedicine.Throughstemcellbiology,itispossibletogenerateanypartsofthehumanbodybystemcellengineering.Considerableresourceswillbedevotedtoharnesstheuntappedpotentialsofstemcellsintheforeseeablefuturewhichmaytransformmedicineasweknowtoday.Atthemolecularlevel,totipotencyhasbeenlinkedtoasingulartranscriptionfactoranditsexpressionappearstodefinewhetheracellshouldbetotipotent.NamedOct4,itcanactivateorrepresstheexpressionofvariousgenes.Curiously,verylittleisknownaboutOct4beyonditsabilitytoregulategeneexpression.ThemechanismbywhichOct4specifiestotipotencyremainsentirelyunresolved.Inthisreview,wesummarizerethestructureandfunctionofOct4andaddresstoOct4functioninmaintainingtotipotencyorpluripotencyofembryonicstemcels.

简介：Nitricoxide(NO)isapleiotropicregulator,criticaltonumerousbiologicalprocesses,includingva-sodilatation,neurotransmissionandmacrophage-mediatedimmunity.Thefamilyofnitricoxidesynthases(NOS)comprisesinducibleNOS(iNOS),endothelialNOS(eNOS),andneuronalNOS(nNOS).Interest-ingly,variousstudieshaveshownthatallthreeisoformscanbeinvolvedinpromotingorinhibitingtheetiologyofcancer.NOSactivityhasbeendetectedintumourcellsofvarioushistogeneticoriginsandhasbeenassociatedwithtumourgrade,proliferationrateandexpressionofimportantsignalingcomponentsassociatedwithcancerdevelopmentsuchastheoestrogenreceptor.ItappearsthathighlevelsofNOSexpression(forexample,generatedbyactivatedmacrophages)maybecytostaticorcytotoxicfortumorcells,whereaslowlevelactivitycanhavetheoppositeeffectandpromotetumourgrowth.Paradoxicallytherefore,NO(andrelatedreactivenitrogenspecies)mayhavebothgenotoxicandangiogenicproperties.IncreasedNO-generationinacellmayselectmutantp53cellsandcontributetotumourangiogenesisbyupregulatingVEGF.Inaddition,NOmaymodulatetumourDNArepairmechanismsbyupregulatingp53,poly(ADP-ribose)polymerase(PARP)andtheDNA-dependentproteinkinase(DNA-PK).Anunderstand-ingatthemolecularleveloftheroleofNOincancerwillhaveprofoundtherapeuticimplicationsforthediagnosisandtreatmentofdisease.

简介：AsapartofabasicresearchprojectonXeno-transplantion,wehavebeenengagedinthederivationofembryonicstemcelllinesfromChineseminiswine.Here,wereportedforthefirsttimetheestablishmentoftwoporcineEGcelllines(BPEG1andBPEG2)fromprimordialgermcellsofgenitalridgesofa28anda27dembryosrespectively.Theirpluripotentnaturehasbeenidentifiedbycolonymorphology,markercharacterizationaswellasbyinvitroandinvivodifferentiation.TheseporcineEGcellsarepotentiallyusefulforfurtherbasicstudies.

简介：One-cellmouseembryosfromKMstrainandB6C3F1strainwereculturedinM16medium,inwhich2-cellblockgenerallyoccurs.EmbryosofKMstrainexhibited2-cellblock,whereasB6C3F1embryos,whichareregardedasanonblockingstrain,proceededtothe4-cellstageinourculturecondition.Itisoftenassumedthattheblockofearlydevelopmentisduetothefailureofzygoticgeneactivation(ZGA)inculturedembryos.Inthisstudyweexaminedproteinsynthesispatternsbytwo-dimensionalgelelectrophoresisof[35S]methionineradiolabeled2-cellembryos.Embryosfromtheblockingstrainandthenonblockingstrainwerecomparedintheirdevelopmentbothinvitroandinvivo.ThedetectionofTRCexpression,amarkerofZGA,at42hposthCGinKMembryosdevelopedinvitrosuggestedthatZGAwasalsoinitiatedeveninthe2-cellarrestedembryos.Nevertheless,asignificantdelayofZGAwasobservedinKMstrainascomparedwithnormallydevelopedB6C3F1embryos.AttheverybeginningofmajorZGAasearlyas36hposthCG,TRChasalreadybeenexpressedinB6C3F1embryosdevelopedinvitroandKMembryosdevelopedinvivo.Butfor2-cellblockedKMembryos,TRCwasstillnotdetectableevenat38hposthCG.Theseevidencessuggestthat2-cell-blockedembryosdoinitiateZGA,andthat2-cellblockphenomenonisduenottothedisabilityininitiatingZGA,buttoadelayofZGA.

简介：VariableChargeX/Y(VCX/Y)isahumantestis-specificgenefamilythatlocalizedonXandYchromo-somes.Inthisstudy,VCYproteinwasexpressedinE.coliintheformofglutathione-S-transferase(GST)fusionprotein.Withthepurifiedfusionproteinasantigen,theanti-GST-VCYantibodywasgeneratedandthelocalizationofVCYproteininhumantestiswasdeterminedbyimmunohistochemistry.Inthetestisseminiferousepithelium,VCYproteinswerehighlyexpressedinnucleiofgermcells.Usingpropidiumio-didestainingandgreenfluorescentprotein(GFP)tagtechnologies,VCYandVCX-8rproteinsweremainlylocalizedinthenucleoliofCOS7cells.Inaddition,thecolocalizationforVCYandVCX-8rinCOS7cellswasalsoobserved.WithVCYcDNAasbait,acDNAfragmentofacidicribosomalproteinPOwasobtainedusingyeasttwo-hybridsystem.AlltheinformationaboveindicatesthatVCX/Yproteinfamilymightbeinvolvedintheregulationofribosomeassemblyduringspermatogenesis.

简介：Acell-freesystembasedupontheeggextractsfromgynogeneticgibelcarp(Carassiusauratusgibelio)orbisexualredcommoncarp(Cyprinuscarpioredvariety)wasdevelopedtoinvestigatedevelopmentalbehaviorsofthedemembranatedspermnuclei.Bothredcommoncarpandgibelcarpspermnucleicoulddecondensefullyandformpronucleiintheredcommoncarpeggextracts.Gibelcarpspermnucleicouldalsodecondensefullyandformpronucleiinthegibelcarpeggextracts,butredcommoncarpspermnucleicouldnotdecondensesufficientlyinthesameextracts.Thesignificantdifferencesofmorphologicalchangeswerefurtherconfirmedbyultrastructuralobservationoftransmissionelectronmicroscopy.Thedatafurtheroffercytologicalevidenceforgonochoristicreproductioninthegynogeneticallyreproducinggibelcarp.Inaddition,thespermnucleiinvitrodecondensationisdependentonthepHintheextracts,andthedecon-densedefficiencyisoptimalatpH7.However,noDNAreplicationwasobservedinthetwokindsofeggextractsduringtheincubationperiodofthespermnuclei.Itissuggestedthattheeggextractspreparedfromthegynogeneticgibelcarpshouldbeavalidinvitrosystemforstudyingmolecularmechanismongynogenesisandreproductionmodediversityinfish.

简介：Phytohormoneabscisicacid(ABA)wascriticalformanyplantgrowthanddevelopmentalprocessesincludingseedmaturation,germinationandresponsetoenvironmentalfactors.WiththepurposetodetectthepossibleABArelatedsignaltransductionpathways,wetriedtoisolateABA-regulatedgenesthroughcDNAmacroarraytechnologyusingABA-treatedriceseedlingasmaterials(undertreatmentfor2,4,8and12h).Of6144cDNAclonestested,37differentialclonesshowinginductionorsuppressionforatleastonetime,wereisolated.Ofthem30and7wereup-ordown-regulatedrespectively.Sequenceanalysesrevealedthattheputativeencodedproteinswereinvolvedindifferentpossibleprocesses,includingtranscription,metabolismandresistance,photosynthesis,signaltransduction,andseedmaturation.6cDNAcloneswerefoundtoencodeproteinswithunknownfunctions.RegulationbyABAof7selectedclonesrelatingtosignaltransductionormetabolismwasconfirmedbyreversetranscriptionPCR.Inaddition,somecloneswerefurthershowntoberegulatedbyotherplantgrowthregulatorsincludingauxinandbrassinosteroid,which,however,indicatedthecomplicatedinteractionsofplanthormones.PossiblesignaltransductionpathwaysinvolvedinABAwerediscussed.

简介：Clusterinisa75-80kDaheterodimericglycoprotein,thatisproducedinmosttissuesbutwhichexactbiologicalroleisstillnotclear.Particularly,itsroleinprotectionorpromotionofapoptosisisheavilydisputed,sincedatasupportingbothviewshavebeenreportedinseveralindependentstudies.Toclarifythisissue,andalsotodeterminewhetherclusterinexpressionitselfmightbeaffectedbyapoptosis,inthepresentstudy,ratthymocytesweretreatedwithdexamethasone,-asyntheticglucocorticoidthatelicitsapoptosisinthymocytes-,andclusterinmRNAexpressionwasanalyzedbysemi-quantitativeRT-PCRbeforeandafterinductionofapoptosis.Interestingly,neitherthetreatmentwithdexamethasoneinvitronortriggeringofapoptosisinvivoup-regulatedclusterinexpression,opposingtheviewthatclusterinisinvolvedinapoptoticprocesses.Ontheotherhand,anewclusterinmRNAisoformwasdetectedandisolated,whoseexpressionwasrestrictedtofreshlyisolatedthymocytes.Thisnovelisoformlacksthepost-translationalproteolyticcleavagesiteandisthereforepredictedtoencodeamonomericprotein.Thebiologicalfunctionundernormalcircumstances,however,willneedfurtherinvestigationsforclarification.Whileapoptosiscouldnotmodulateclusterinexpression,activationofthymocyteswithconcanavalinAandinterleukin-2resultedinup-regulationofclusterinmRNAlevel,indicatingthatclusterinexpressionisratherunderthecontrolofcellactivation-mediatedratherthanapoptosis-inducedsignals.

简介：Thec-erbB-2proto-oncogeneencodesa185kDaproteinp185,whichbelongstoepidermalgrowthfactorreceptorfamily.Amplificationofthisgenehasbeenshowntocorrelatewithpoorclinicalprognosisforcertaincancerpatients.ThemonoclonalantibodyA21whichdirectedagainstp185specificallyinhibitsproliferationoftumorcellsoverexpressingp185,henceallowsittobeacandidatefortargetedtherapy.InordertoovercomeseveraldrawbacksofmurineMAb,wecloneditsVHandVLgenesandconstructedthesingle-chainFv(scFv)throughapeptidelinker.TherecombinantscFvA21wasexpressedinEscherichiacoliandpurifiedbytheaffinitycolumn.SubsequentlyitwascharacterizedbyELISA,Westernblot,cellimmunohistochemistryandFACS.Alltheseassaysshowedthebindingactivitytoextracellulardomain(ECD)ofp185.BasedonthosepropertiesofscFvA21,wefurtherconstructedthescFv-Fcfusionmoleculewithahomodimerformandtherecombinantproductwasexpressedinmammaliancells.Inaseriesofsubsequentanalysisthisfusionproteinshowedidenticalantigenbindingsiteandactivitywiththeparentantibody.Theseanti-p185engineeredantibodieshavepromisedtobefurthermodifiedasatumortargetingdrugs,withaviewofapplicationinthediagnosisandtreatmentofhumanbreastcancer.