BIPN 144 Week 5 Notes(part 2)

BIPN 144 Week 5 Notes(part 2) - BIPN144Week5Notes

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Unformatted text preview: BIPN144Week5Notes Note:ThishasnotbeenreviewedbyDr.Bierandmayhaveerrors.Always trusttheprofessoroverthesenotes. Thursady Dr.Bierstartedlecturewiththebelowimageandadiscussionaboutthecompound eye. Heypointedoutthatlookingthroughacompoundeyeisnothinglikelooking throughakaleidoscope.Insteaditprovidesalowresolutionimage,butwithvery highspeed,aseach"eye"(andIthinkhereeyemeansfacetofacompoundeye) connectsdirectlytothebrain.Manyanimals,likethemongoose,seeveryfast.Each "eye"has8cells. Aflylarvaehasasortof"preeyesack."Inthissackistheimaginaldisc,illustrated inAandBabove.TheprocessillustratedinBaboveisimportanttounderstand.This ismidwaythroughaprocess.ThisprocessbeginswithHedgehogsignalingonthe posteriorendoftheimaginaldisc.HedgehogactivatesDPP.Dpp,inturnactivates theproductionofmorehedgehog.(Thisisapositivefeedbackloop.)Dppisonly producedinfrontofHhexpression,notintheareawhereHhisalreadybeing produced. WhereDppisactivethetissueisslightlyindented.Thisindentedareaiscalledthe furrow.AstheareaexpressingHhexpands,thefurrow`moves'likeawavefromthe posteriorendofthedisctowardstheanteriorend. FigureCaboveshowsthatthedevelopmentofeyecellsiscompletedfirstinthe posteriorendoftheimaginaldisc,whereHhsignalingstarted.Overtime,themore anteriorcellscatchup.FigureCalsoshowshoweyecellsarerecruitedtotheR8cell overtime.howeverthisisnotthatimportantforustoknow.CellR8developsfirst. R8cellsareseparatedbynotchsignaling.R8theninducesothercellstohelpform theeye.Thesecellsarealinducedbythesamesignalingmethod,exceptR7,whichis inducedlast.R7cellsareinducedbytheBoss/Sevenlesspathway. Finally,figureDgivesusourfirstintroductiontotheBossLigandandthesevenless receptor.R8cellsproduceBoss,whichsignalstothesevenlessreceptoronR7cells. R7cellsareresponsibleforseeingUVlight.AcleverscientistnamedBillperformed aUVbasedassaytofindUVblindflies.Hediscoveredthatmutantslackingthe sevenlessreceptordevelopednoR7cells.Laeronitwasdiscoveredthatmutants lackingtheBossligandwerelikewiseUVblindandhadnoR7cells. DrBierthenpresenteduswiththeBoss/SevenlessPathway. Interestingfunfact:Bossisshortfor`brideofsevenless.'Sos,anotherproteininthe pathwaystandsfor`sonofsevenless' Irrelevantfact:SonofSamwasthenameofaserialkillerwhowasarrestedin1977. Atonepointheclaimedthathecommittedhiscriminalactsbecausehisneighbor's dogtoldhimto.Seriously.Prettymessedup.WhydoIknowthisstuff? BelowistheBoss/SevenlessPathway. Boss -> Sevenless Signaling in Drosophila R7 Photoreceptor Sevenless BOSS Drk Sos RAS-GTP Raf KSR RAS-GDP GAP Dsor (MAPKK) Rolled (MAPK) Signaling Cell (R8) Receiving Cell (R7) NUCLEUS Pnt Phyl Yan PO 4 Pnt PO Yan 4 Phyl R7 FATE SOhereiswhat'sgoingon.NormallySevenlessisaproteinmonomerfloating aroundinthecytoplasm.WhenBoss,bindstosevenless,itcauses2sevenless monomerstodimerize.Onesevenlesschainthenphosphorylatestheotherresulting inalotofdeliciousnegativecharges.Ataboutthispoint,DrkandSosjointheparty. Drkdockstothesevenlessdimmer,andSos(sonofsevenless,notSonofSam)is attachedtoDrk.SosactsasacatalystinthephosphorylationofRASGDPturningit intoRASGTP.ThisisimportantbecauseRASGTPisactive,whereasRASGDPis inactive.GAPcanlikewiseinactivateRASGTPbydephosphorylatingit,convertingit backintoRASGDP.RASGTPactivatesRaf,RafactivatesDsor,andDsoractivates Rolledwhichslipsintothenucleus. BeforeRolledgetsintotheNucleus,hereiswhat'sgoingon: Pntisinactive. Yanisactive. YanisactivelyrepressingPhyl. AfterRolledworksitsmagic,hereiswhat'sgoingon: PntandYanarebothphosphorylated. ThisinactivatesYan. ItalsoactivatesPnt. PntactivatesPhyl,leadingtotheR7fate. AflycanstillgetbyseeingUVlightwithonlyonegoodcopyofsevenless.(However multipleheterozygousmutationslikesevenlessANDSoscanrenderaflyUVblind) NowtheMosaicAssay!! Careful,thisiswhereeverythinggetscrazy!Thisexperimentisdoneinsevenless heterozygous(+/)mutants.Whenanearlyeyecellisreadytodivide,itwilldouble itsDNA.ByzappingthisdoubledDNAwithanXRay,scientistscaninducegene mismatchingintheresultantdaughtercells.Thatis,insteadofeachdaughtercell gettingonegoodcopyandonebadcopyofthesevenlessgene,onedaughtercelss willgetbothgoodcopies,andtheotherwillgettwobadcopies.Asthesecells continuetodivide,theywillresultinalargelyheterozygous(+/)eye,withclusters ofwildtype(+/+)cellsandfullmutantKO(/)cells. ThescientiststheexaminedtheedgewhereKO(/)cellclustersmetupwith Heterozygote(+/)cellclusters. Alongthisedge,thescientistssearchedforeyecellclustersthathadhadanR7cell. TheythenaskedthemselvesinthesecellclustersthathaveR7cells,whichcells(R1 R8)haveamutantcopyofsevenless. Thisisreallyachallengingconcept,andIwillcoveritinSectiontoday,butIlltryand makeitclearerheretoo.RememberthateyeformationstartswithR8cells,which theninduceneighboringcellstobecomepartoftheeyecluster.Alongthemutant/ normaledgeinourXrayzappedflyeye,anyoneofthecellsthatformtheeye cluster(R1R8)couldpotentiallybeoneofthesevenlessKO(/)mutantcells.The scientistswantedtoknowwhichcellinthecluster(R1R8)neededtohavea functionalsevenlessgeneinordertogiverisetoanR7cell.Theyaccomplishedthis bylookingatmultipleeyeclustersthathadafunctionalR7cell,andrecordingwhich cellsineachoftheseclustershadmutant(/)copiesofsevenless.Theydiscovered thatineyeclusterswithafunctionalR7cell,anyofthecellscouldhavemutant copiesofsevenless,exceptforR7. SofirsttheyfounttheKO/Normalborder ThentheyidentifiedclusterswithafunctionalR7cell Thentheywentthroughtheindividualcells(R1toR8)inthatclusterandrecorded whichhadKOmutant(/)copiesofsevenless. IntheseborderclusterstithfunctionalR7cells,TheyfoundR1cellswithmutant copiesofsevenless,R2cellswithmutantcopiesofsevenless,R3cells,R4cellsR5 cellsR6cells,andR8cells,allwithmutantcopiesofsevenlessbutnoR7cellswith mutantcopiesofsevenless.Theythereforeconcludedthatfunctionalsevenless geneswererequiredinandonlyintheR7cellinordertohaveaneyeclusterwitha functionalR7cell. AfterthisDrBierbrieflydescribedthefollowingfigure,showingdevelopmentofthe vertebrateeye.Thiswillbediscussedmoreinmynotesforweek6. ...
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