AntibodyLabeling ThinsectionsofBIOLOGicalmaterial,mountedonspecimengrids,canbeeasilylabeledbyfloatingthem,section-sidedown,onsmalldropsofantibody.Thismethodwillworkforsectionsthroughresin-embeddedmaterialaswellasforthin,thawed,cryosections. IfalongpieceofParafilmisstucktoabenchbenchsurfacewithadropofwatertheantibodyincubationsandwashingstepscanbeperformedonthecleansurfaceoftheparafilm.Onlyexposeasmuchoftheparafilmasitisneededanddonotcontaminatethecleanparafilmsurface.Antibodylabelingprotocolsareavailableontheantibodylabelingpage.Asimplelabelingprocedureissummarizedbelow. Any"sticky"proteincanbeusedtocovernon-specificbindingsitesonthethawedsections.Beawarethatthechosenproteinmustnotreactwithanyoftheaffinityreagentstobeused(e.g.rabbitserumcannotbeusedwithproteinAgold;bovineserum(FCS)cannotbeusedasablockingagentifanti-BSAlabellingisbeingstudied). Weroutinelyuse10%FCSinPBSasablockingagent,butBSA,gelatin,ovalbuminandcoldwaterfishskingelatinhavebeenused.TheblockingagentsusedonWesternblotsshouldalsoworkonthesesectons. To"quench"freealdehydegroupsthatmaybepresentinthesection0.15%glycinecanbeaddedtotheblockingsolution. Specimengridsarefloatedwiththesidecontainingthesectionsontheliquid.DropsofPBS,ordilutedantibodies,areplacedonthecleansurfaceofparafilm.Thegridsaretransferredfromdroptodropontheparafilm.Makesurethesectionsdonotdryout.Theparafilmiskeptcovereduntilreadytouse. Theantibody,dilutedtoasuitableconcentration,inPBScontainingblockingagent,iscentrifugedfor1mininanEppendorftubebeforeuse.Thiswillremoveanyaggregatesformedduringstorage. Placesmalldropletsofantibody(3to5microliter)ontheparafilmsurfaceandfloatthegrids,withsectionsdown,onthem.Thegridsaretransferredfromtheblockingsolutionusingfineforceps.Toensurethattheantibodydropletsdonotdryout(andconcentrate)placeawetpieceoffilterpapernearthemandcoveritandthemwithaplasticdish. Afterantibodyincubationthegridsareremovedfromtheantibody,withforceps,andplacedontolargedropsofPBSontheparafilmsurface.Transferthegridsfromdroptodropeitherwithforcepsoralargewireloop.Takecarenottowetthetop,drysurfaceofthegrid. Liketheantibody,theproteinA-goldisdilutedinPBSwithblockingagentbutitisnotcentrifugedpriortouse.SmalldropletsofdilutedproteinA-gold(samevolumesasusedfortheantibodies)areplacedontheparafilmsurface,thegridsareplacedonthedropsandtheyareleftcoveredduringtheincubation. GohereifyouwanttoseeamethodofmakingcolloidalgoldprobesandcouplingthemtoproteinssuchasproteinA. Thisisthesameaswhenwashingafterantibodyincubation.Againtakecarenottowetthebackofthegrid. Althoughonlyashortwash,THISSTEPISVERYIMPORTANT.DONOTFORGETIT!Thisstepremovesallphosphatemoleculespriortoincubationwithuranylacetate.Phosphatespresentinthesectionswillprecipitatetheuranylsalts. Oncetheantibodyreactionshavetakenplacetheonlythinglefttodoisthefinalcontrastinganddryingstepwhichwillenableustoexaminethesectionsintheelectronmicroscope.Procedure
Blocking
Antibodylabeling: AntibodyIncubation
PBSWash
ProteinA-goldIncubation
PBSWash
WaterWash