RationaleTheuseofmousegeneticmodelsrequiresanefficientsystemofuniqueanimalidentifiers.Themeansthattissuemustbeobtainedfromeachanimalforgenotypingandthateachanimalmustbetaggedsoitcanbequicklydistinguishedfromotheranimals.Avarietyofmethodshavebeenemployedtotagmiceincludingeartags,earpunches,tatoosandsubcutateouschips.Noneoftheseapproachesprovidetissuesotheymustbecoupledwithatissuebiopsy,usualyapieceoftailtip,forgenotyping.Alternatively,toebiopsyapproachsimultaneouslyprovidestissueandarecognizableidentifiertodistinguishanimals.Toebiopsieshaveotheradvantages,namelytheydonotcausechronicforeignbodyirritation,havelessinfectionpotential,cannotfalloffandrequirenospecializedequipment.(1-6)Thepotentialsideeffectsoftoebiopsiesaresimilartothatoftailbiopsiesandareminimalifanimalsarebiopsiedintherecommendedagerange,anddonothavehealthproblemsatthetimeoftheproceduresuchasskindiseases,impairedimmunityorthrombocytopenia.Likeallliveanimalprocedures,mouseidentificationrequirespropertrainingandpriorIACUCapproval.Forgenotypingproceduresthatareammenabletoaminimalamountofinputmaterial,cheekswabsarealessinvasivealternativetotoeortailbiopsies,butdoneedtobecoupledwithapermanenttaggingprocedure.(7)ApproachMousepupstypicallyspend3weekswiththeirmothersbeforebeingweaned.Duringthefirstweektheyaretoosmallforlongtermidentifcationmethods.Between7and10daysofagetheirtoesbecomewellseparatedandcanbebiopsiedwithsmalldissectingscissors.Atthisagethetissueisstillsoftandthetoebiopsyprocedureappearstocauseminimaldistress.A7dayoldpup,forexample,willtypicallyobjectmoretobeingpickedupandseparatedfromitslittermatesthanitwilltohavingitstailortoesbiopsied.Atolderages,mousepupsbecomemorealertandthetoetissuebecomesfirmerfromossification.Itispreferabletouseyoungeranimalsbecauseolderanimalsrequireadditionalstepsaretakentoprovideanalgesia(e.g.withinhaledisoflourane)andensurehemostasis.Theuseofanesthesiticssignificantlyincreasestheriskoftheproceduresobiopsiesshouldnotroutinelybeperformedonolderanimals.Procedure1.Theoperatorshouldwearglovesandprotectiveclothingasperroutineprotocol.2.Pickupamousepupbythescruffoftheneck.Whenholdingamousedonotsqueezetheanimalsohardthatitsbreathingisimpaired.Donotholdittoolooselyoritwillsquirmandbecomeagitated.Takingcaretoholdamouseproperlyisthemostimportantaspectofensuringitscomfortandsafety.3.Withasharppairofdissectingscissorsremoveamousetoeandletthetissuefallintoa1.5mLmicrocentrifugetube.Ifmorethanonetoeisbeingcollectedthenpoolthemintothesametube.Itisimportantdissectthetissueproximaltotheinterphalangealjointssoitcaneasilyberecognizedinthefuture.4.RefertothetoenumberingschemetoidentifytheanimalswithauniqueID.Thesystemusesatmosttwotoesfromeachfootandprovides0-9999uniqueIDs.InpracticesmallernumberscanbeusedaslongascareistakennottoaddthattwomicewiththesametoeIDstothesamecage.Cagescardsandinventoryrecordsshouldincludethecompleteuniqueidentifierforeach.5.Placethepupswhichhavebeenidentifiedintoanewcagetodistinguishthemfromtheirlittermates.Whenallofthepupshavebeenidentified,returnthepupstotheirmotherscage.6.PrepareDNAfromthetissuesaccordingtotheTailDNAprepprotocol.7.EnterthenewPupIDsintothemurinepathologydatabase(MPD)alongwithgenotypeinformationwhenitisavailable.References1.BaronBW,LanganG,HuoD,BaronJM,MontagA.SquamouscellcarcinomasoftheskinateartagsitesinagedFVB/Nmice.CompMed.2005Jun;55(3):231-5.2.CoverCE,KeenanCM,BettingerGE.EartaginducedStaphylococcusinfectioninmice.LabAnim.1989Jul;23(3):229-33.3.WaalkesMP,RehmS,KasprzakKS,IssaqHJ.Inflammatory,proliferative,andneoplasticlesionsatthesiteofmetallicidentificationeartagsinWistar[Crl:(WI)BR]rats.CancerRes.1987May1;47(9):2445-50.4.LeCalvezS,Perron-LepageMF,BurnettR.Subcutaneousmicrochip-associatedtumoursinB6C3F1mice:aretrospectivestudytoattempttodeterminetheirhistogenesis.ExpToxicolPathol.2006Mar;57(4):255-65.5.NadonNL,DraegerK.GenomicDNAanalysisfrommousetoelysates.TransgenicRes.1996May;5(3):209-11.6.VachonP.Anatomicalandhistologicalobservationsoffore-andhindlimbtoesinadultmiceafteramputationsperformedattheageoftwoweeks.CanJVetRes.1998Oct;62(4):311-3.7.MeldgaardM,BollenPJ,FinsenB.Non-invasivemethodforsamplingandextractionofmouseDNAforPCR.LabAnim.2004Oct;38(4):413-7.