BIPN 144 Week 8 Notes (part 1) (2)

BIPN 144 Week 8 Notes (part 1) (2) -...

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Unformatted text preview: BIPN144Week8Notes(Part1) Note:ThishasnotbeenreviewedbyDr.Bierandmayhaveerrors.Always trusttheprofessoroverthesenotes. Today'sTopicwasCellDeath!Mwahahaha! Dr.Bierstartedwithexamplesfromthewormworld.Hefirstpointedoutthatthe completecelllineageofthewormC.elegansismapped.Soaseachcelldivides,we nowexactlywhatitwillbecomeandwhereitwillgo.Thisisparticularlyinteresting becauseseveralcellsareprogrammedtodie!ThisleadtothediscoveryoftheCED genes(andEgl1). Apoptosisisprogrammedcelldeath,thisisdifferentfromzappingacellwithalaser. Inapoptosisacellthecelldecidestoterminateitselfproperly,itisgenetically regulated,anddifferentfromrandomkilling.Thecellevencutsupitsowngenetic materialtobereabsorbedbytheorganism,andpreparestodiewithoutcausinga lotoftrouble. IntheCEDmutants,thecellsthatshouldhavedied,didnotdie.Thiscaughtthe scientist'sattention.HereisanoverviewofwhatthedifferentCEDmutantsdid: Ced3or4mutantscelldeathwasblocked Ced9mutantsextracelldeath Egl1Mutantblockedcelldeath Ced9/Ced3doublemutantnocelldeath Egl1/Ced9doublemutantextracelldeath Afteralltheseexperiments,thispathwaywasestablished: Egl1--XCed9--XCed4Ced3Apoptosis Egl1inhibitsCed9.Ced9inhibitsCed4.Ced4activatesCed3.Ced3leadsto apoptosis.Thoughitdidn'tshowupinthescreens,cytochromecisalsoinvolved. Thisprocessishighlyconservedacrossspecies. Mouseequivalents: Egl1=Bax Ced9=Bcl2 Ced3=Caspace3 Ced4=Apaf Howitworks:PleaseStudyfigure7.23and7.27inthetextbook! IntheCellmembrane,thereisasortofequlibriumbetweenBCL2andBAX.Ifthere ismoreBCL2thanBAXthecelllives. IfthereismoreBAXthanBCL2thecelldies! WhenthereismoreBaxthanBCL2,BaxdestabilizestheMitochondriaand CytochromeCgetsoutandactivatesApaf.Apafcleavesprocaspace9,activating caspace9.Caspace9cleavesprocaspace3,activatingcaspace3.Caspace3frees CAD,anucleaseresultingincelldeath! Dr.Bierthendescribedanexperimentcarriedoutinvertebrates. Normally,theorganismgeneratesmoremotorneuronsthannecessary.Some undergoapoptosis,andyougetwhatweseeontheventrallefthandside.If, however,themuscle(s)thatthemotorneuronsusuallyinnervateisexcised,then evenmoremotorneuronsthannormalundergoapoptosis(righthandside). Conversely,ifyougraftinanadditionallimb(notpictured)thenahigherthan normalnumberofmotorneuronssurvive. Dr.BierthenintroducedustotheconceptofNeurotrophins,themostimportantof whichisNGF.ScientistsnoticedthatNGFexpressingtumorsinmiceattractedaxons fromthenervoussystem.Invitro,anNGFexpressingtumorwouldalsoattract axonsfromNStissue.NDFalsorescuescellsfromcelldeath.ThereceptorforNGFis TrkA.NGFbindsTrkAwithahighaffinity.Atthesametime,NGFalsobindsp75, withalowaffinity.TrkAisareceptortyrosinekinase.Thereisanexcellentfigurein thebookwhichnamesafewTrophicfactorsandtheirreceptors.Belowisa simplifiedrecreation. Hediscussedacouplemutants: NGFKOmouselookslikeTrkAKOmouse BDNFKOmouselookssimilar,butnotassevereasTrkBKomouse(stillhasNT4/5 activity) BDNF/NT4/5doubleKOlooksaboutthesameasTrkBKO. ThethreeimportanteffectsofNGF: 1) itisatrophicfactorrequiredforcellsurvival 2) Itisasignalthatpromotesaxonoutgrowth 3) Itisanattractivecuethatattractsaxons DrBierMentionedtwootherexperimentsinvolvingNGF. ThefirstdemonstratedthatNGFcanbetakenupbytheneuronsthroughtheaxonin aretrogradefashion.RadiolabeledNGFwasimagedorotherwisemonitoredasit movedupanaxon.Thisjourneytakesuptoseveraldays.NGFcanalsobepickedup directlyfromthecellbodyifitispresentnearthecellbody. Thenexycetofexperimentstookplaceina Thenextsetofexperimentstookplaceinacrazythreechamberedsystem Theneuronsarealwaysplacedintheenterchamber(ChamberC). Experiment1NGFwasputinallchambers. Results:NeuronsinCsurvived,andsentneuronsintoallchambers Experiment2NGFwasputinchamberConly. Results:Theneuronssurvived,butdidnotextendaxonsintootherchambers Experiment3NGFwasputinChamberAonly. Results:NeuronssurvivedandextendedneuronsintoChamberAonly. TheseexperimentssupportthethreeimportantfactsaboutNGFlistedabove. Dr.BierthendiscussedthedifferencesbetweenEGFandNGFSignaling. EGFcausesPC12cellstoProliferate,whereasNGFcausesthemtodifferentiate. Peoplewantedtoknowwhy. Theydidchimericreceptorstudies,andfoundthattheextracellularpartsoftheEGF andNGFcouldbeswitched.WhenthiswasdoneEGFadministrationwouldthen causedifferentiation,andNGFadministrationwouldcauseproliferation.They determinedthattheintracellulardomainsofthesereceptorswerethemost importantpartsindeterminingtheoutcomeofstimulation. TheyalsofoundthatactivationoftheEGFreceptorresultedinashortburstof signalingthatquicklytaperedoff.WhereasactivationoftheoftheNGFreceptor resultedinamoresustainedlevelofsignaling. Theyalsodidanexperimentwheretheyexposedthecellstoreallysuper ridiculouslyhighlevelsofEGF.BecausetherewassomuchEGF,thereceptorswere continuouslystimulatedforalongduration.Thislengthydurationofstimulation mimickedthesustainedstimulationcausedbyNGF,andasonewouldexpect resultedindifferentiation. ...
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This note was uploaded on 11/10/2010 for the course BIPN BIPN 144 taught by Professor Bier during the Spring '10 term at UCSD.

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