BIPN 144 Week 5 Notes(part 1)

BIPN 144 Week 5 Notes(part 1) - BIPN144Week5Notes(Part1)

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Unformatted text preview: BIPN144Week5Notes(Part1) Note:ThishasnotbeenreviewedbyDr.Bierandmayhaveerrors.Always trusttheprofessoroverthesenotes. Dr.BierStartedlecturebyreviewingthenotchsignalingsystem,whichhadrecently beenmadefamousbythemidterm,question#5.Hethendisplayedthefollowing image: Thisimagedepictstheseparationofaneuroblastfromtheneuroectoderm.Thetop pictureshowsaneuroblastdelaminating.Thenextimagedownshowsthe neuroblastandepithelialcells.Eachcell'splaneofdivisionisshownbyadashed line.Notethattheneuroblastplaneofisparalleltotheepithelium,whereasthe Epithelialplaneofdivisionisperpendiculartotheepithelium.Thenextportion downiswherethingsgetinteresting(describedfromlefttoright).Bazooka,coming downfromtheepithelium,causesInscutableandPinstocollectatthetopofthecell. ThesefactorsworktostopNumb/Prospero/Mirandafromaccumulatinginthetop ofthecell,sotheyaccumulateinthebottomofthecellinstead. Thesefactors(Numb/Prospero/Miranda)aregreatexamplesofLocalized Determinants.Alocalizeddeterminantisamoleculethatisasymmetrically distributedduringcelldivisionthatinfluencesthefateofthecellthatinheritsit. Thethirdimagefrotheleftshowsthatthesefactorsarestillasymmetrically distributedatthetimeofcelldivision.Theyellowthingsarethemitoticspindle poles.NotethatbythispointInscutableandPonshavedissipated. Thefinalimageisthetrickiestbecauseitrepresentsseveralmomentsintimeallat once.Thedivisionoftheneuroblastgivesriseto:1)anewneuroblast,indicatedby theUturnarrowanda2)Ganglionmothercell(GMC,showninpurple).ThisGMC willthendivideonce,intotwodaughtercells,eachwillbecomeaneuron.Overtime asthisentireprocessisrepeated,theseneuronswillformclusters.AccordingtoDr. Bier,inmetamorphicanimals,thenumberofneuronsintheseclusterswillincrease anddecreaseduringthedifferentdevelopmentalstagesoftheanimal'slife. Prosperoisresponsibleforturningoffthe"neuroblastgene"IfProsperoisknocked outthenthecellthatwouldnormallybecomeaGMCgetsconfused,andtriestobe bothaneuroblastandaGMC.Asusual,thisresultsincelldeath. ThiswholeneuroblastdivisionsystemiswhatoccursintheCentralNervoussystem. InthePeripheralNervousSystem,thingsareslightlydifferent.ThePNSequivalent ofaNeuroblastiscalledasensoryorganprecursor(SOP).Unlikeaneuroblast,the SOPdoesn'tselfrenew,itcreates2daughtercells,eachofthesedaughtercellsthen divideagain,yieldingatotalof4cells. DrBierthenDescribed3differentSensoryorgansformedbytheflyPNS,the MultipleDendriteCell(MD),theExternalSensoryOrgan(ES),andtheStretchor ChordotonalOrgan(CHO). TheMDistheeasiesttounderstand.TheSOPdividesinto2cells,andeachofthese cellsdividesagain,yielding4cells.Eachofthesecellsthenbecomesaneuronwith lotsofdendrites.Thesecellsactastouchreceptors.Theyareverysimple. Thenextorgan,theESorgan,ismorecomplex,itlookslikethis: Therearefourmainpartstothisorgan,theHairCell,theSocketcell,theGlialCell, andtheNeuron.Thehaircelldetectsmovementandwiggles.Thiswiggling stimulatestheendofthedendritefoundatthebaseofthehaircell.Thissendsan impulsetothecellbodyanddowntheaxontotheCNS.TheGlialcellwrapsaround thedendrite,andhelpswithsignaling.SoonI'llgooverhowthisorgandevelops. TheCHOlookslikethis,itisresponsiblefordetectingstretch. Thisorganconsistsofasheathcell,acapcell,aneuronandaligamentcell.The sheathandligamentcellseachhaveoneendattachedtotheepithelium,shownhere asaperpendicularblackline.WhentheCHOisstretched,thesheathcelltugsonthe capcell.Thecapcelltugsontheneuron'sdendrite,andthedendritesignalstothe neuron,whichcommunicateswiththeCNS. Afterintroducingthese3organtypesDr.Bierdescribedanexperimentthatwas designedtodeterminewhatmadeanSOPbecomeanESorganinsteadofaCHOor thereverse.ThescientistfocusedinonaTranscriptionFactorcalledcut.Under normalconditions,anESSOPwillexpresscut,andaCHOSOPwillnot. Thescientistthengeneratedacut()mutant.Intheabsenceofcut,SOP'sthatcould normallyhavebecomeESSOP'sbecameCHOSOP'sinstead.Thescientistthen forcedcutexpressioninallSOP's,andtheSOP'sthatnormallywouldhavebecome CHOSOP'sbecameESSOP'sinstead.Thescientistconcludedthatcutdeterminesthe fateoftheseSOP's.Thesefindingsaresummarizedgraphicallyinthefollowing diagram. DrBierthenexplainedNotchsignalingonemoretime,andthenshowedusthethe SOPlineagethatproducesanESorgan. WestartwithanSOP.Numbaccumulatesinthebottomportionofthecell.TheSOP thendivides.CellIIbgetsthemajorityoftheNumb.CellIIadoesnot.Thereisthen somenotchsignalingbetweenthesetwocellstodeterminewhichwillmaintain neuralpotential.However,inthiscasethediceareloaded.Numb,bindstothenotch receptorresultinginreducednotchactivity.Withthisadvantage,cellIIbwinsthe notch/deltatugofwar.CellIIathendividesformingthesocketandhaircells.Cell IIBdividesagainaswell,andonceagainoneofthetwodaughtercellswillhave morenumbthantheother.Thesetwocellswillonceagainundergonotch/delta signalingtodeterminewhogetstobetheneuronandwhogetstobetheglialcell (Ew!Whowouldwanttobeaglialcell!)Thecellwiththenumbismorelikelytowin thenotch/deltatugofwarandbecometheneuron!Thissystemensuresthatweget oneofeachtypeofcellrequiredtomakeacompleteESorgan. ...
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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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