BIPN 144 Week 7 Notes (part2)

BIPN 144 Week 7 Notes (part2) - BIPN144Week7Notes(Part2...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: BIPN144Week7Notes(Part2) Note:ThishasnotbeenreviewedbyDr.Bierandmayhaveerrors.Always trusttheprofessoroverthesenotes. Dr.BierbeganthisdaywithareviewoftheSperryexperimentandthehemisected retin/hemisectedtectumexperiments.HealsopointedoutthatEphinteractionis repulsive. TheaxonshaveasortofsetpointofhowmuchEphtheycantolerate,andwhenthey reachthatpointtheystop. Here'sananalogy,thinkoftheaxonsasboatssailingtowardthetectum.Eph Receptorsarelikeholesinthetopoftheboat.Asyouapproachtheposteriorendof thetectum,theweathergetsworseandworsewithmoreandmorerain.Itwilltake longerforboatswithonlyafewholes(NasalRetina)tofillwithrainandsinkthan boatsthatareriddledwithholes(TemporalRetina).Ihopethathelps. Hethendescribedanexperimentwheretheresearcherscutoutdifferentareasof theretinal.Theythentookanteriorandposteriorportionsofthetectumandground themup,andeliminatedeverythingbutthesurfacereceptors.Theythenplatedout theeyesonsubstrateformedfromthegrounduptectum. TheNasalmostretinalaxonsdidn'treallycareiftheyweregrowingonAnterioror posteriortectum,however,theTemporalmostretinalaxonscouldn'thandlethe stenchofEphontheposteriortectum,andgotovertotheAnteriortectumasfastas possible.SeeBelow. NasalRetinalaxonsarerelativelyinsensitivetoEph,whereasTemporalRetinal axonsareverysensitivetoEph. DrBierthenmentionedthatfishkeepgrowingtheirentirelives.Theireyesand tectumgrowtoo.Buttheretinagrowsradially,whereasthetectumjustextends.In ordertomaintaintheproperneuralgeography,thenewformingnasalmostretinal axonssortofinvadetheedgesoftheanteriortectum,andcrowdtheotheraxons over.Thetemporalmostretinalaxonssimplyprojecttothenewlyformedposterior tectum. Theimportantthingstounderstandabouttheseexperimentsare: 1) only2molecules(EphandEphreceptors)cancontrolthisentireprocess (muchsimplerthanthesperrychemoaffinitymodel).And 2) thissystemcanbetterexplainhowthefisheyegrows,andtheresultsofthe hemisectionexperimentsthancantheChemoaffinitymodel. Drbierthendiscussedthetheformationoftheflyvisualsystem.Erlyonfibers projectfromthelightsensitiveBuldwig'sOrgantowardthebrain.Thesepioneer fibersareusefulforhelpingothernervefiberstofindtheirwaylateron.A researcherobservedthatinsomemutants,errorsoccurredinthispathfinding process,andthisleadtothediscoveryofDSCAM.DSCAMisareceptorself adhesivemolecule,howeverthisselfadhesioncausesrepulsion!(KissandSplit) Thepathwaylookssomethinglikethis: DSCAMDockPAK(kinase)Rho/Rac/CDC42Actin/Myosin(growth cone). AllknownpathfindingcuesgothroughtheRho/Rac/CDC42pathway. FlyDSCAMisaverycoolgene.Itconsistsofatleast9exons.Oftheseatleast threeexonshavemultiplevariations.Exon4has12forms,exon6has48forms andexon9has33forms.Thismeansthatthereare30,000differentpossibilities forDSCAM.AndtheDSCAMProteinsaresoprecisethattheonlyselfadhere whenbothDSCAM'sareidentical.EachcellmakesonlyafewDSCAMsplice variations.Thiseffectivelygiveseachindividualneuronawayforitsbranchesto recognizeandrepulseoneanother,buttogetalongjustfinewithbranchesfrom otherneurons.BranchesofthesameneuronwillexpressthesameDSCAMsplice variationsandrepulseeachother.Branchesfromdifferentcellswillhave differentDSCAMsplicevariations,andwillnotrepulseeachother. ThisisparticularlyimportantinMushroombodies,astructureintheflybrain thatisassociatedwithlearningandmemory.TheMushroombodyhasalong projectionthatbifurcates.Atthebifurcationpoint,DSCAMselfadhesion,andthe resultantrepulsionareresponsiblefordirectingthebifurcatingaxonal projectionawayfromtheaxonbranchthatcontinuesintheprimarydirection.If thereisnoDSCAM,thesetwobrancheswouldadheretogetherinsteadofgoing offinotherdirections.IfthesameisoformofDSCAMisforcedtobeexpressedin allneurons,thenthebranchesoftheseneuronsallrepulseeachother,andflyoff indifferentdirections.Icantimaginethatthatanimalwouldbeveryhappy. ...
View Full Document

  • Spring '10
  • Bier
  • axonssortofinvadetheedgesoftheanteriortectum,andcrowdtheotheraxons over.Thetemporalmostretinalaxonssimplyprojecttothenewlyformedposterior tectum, TheNasalmostretinalaxonsdidn'treallycareiftheyweregrowingonAnterioror posteriortectum,however,theTemporalmostretinalaxonscouldn'thandlethe stenchofEphontheposteriortectum,andgotovertotheAnteriortectumasfastas, Drbierthendiscussedthetheformationoftheflyvisualsystem.Erlyonfibers projectfromthelightsensitiveBuldwig'sOrgantowardthebrain.Thesepioneer fibersareusefulforhelpingothernervefiberstofindtheirwaylateron.A, otherneurons.BranchesofthesameneuronwillexpressthesameDSCAMsplice variationsandrepulseeachother.Branchesfromdifferentcellswillhave differentDSCAMsplicevariations,andwillnotrepulseeachother
Ask a homework question - tutors are online