BIPN 144 Week 4 Notes

BIPN 144 Week 4 Notes - BIPN144Week4Notes

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Unformatted text preview: BIPN144Week4Notes Note:ThishasnotbeenreviewedbyDr.Bierandmayhaveerrors.Always trusttheprofessoroverthesenotes. Becausewehaveonlyashorttimebeforethemidterm,Ihavedecidedthatinstead ofdoingathoroughwriteupofTuesdayslectureandsendingitoutaftertheexam,I willdoanabbreviatedwriteup,focusingonkeyfeaturesandsenditoutnow. Signalinginthevertebrateneuraltube. Thetopimageillustratesanormallyformingneuraltube.Asinthepartitioning modeloftheflyneuroectoderm,therearetwoopposingfactorswhicharelargely responsibleforactivating/repressinggenes.Shh(analogoustoDorsal)isactivein theventralregionsandisproducedoriginallyfromthenotochord,andlaterbythe floorplate.BMP'scomprisethedorsalsignal.Theyareproducedoriginallyfromthe nonneuroectodermandlaterfromthedorsalmostportionoftheneuraltube. AcrazyscientistdidsomeSpemannlikeexperimentsbygraftinginanadditional notochordthisisdepictedinthelowerimage.Asyoucansee,itwasabletoalter thedevelopmentoftheneuraltubeandgeneratedasecondfloorplate,etc.He repeatedthisexperimentwithabeadsoakedinShhinsteadofanotochordandgot thesameresults.Healsoattemptedgraftinginalaterstagedfloorplate,andagain gotthesameresults. SonicHedgehog(Shh)Signaling Inthevertebrateneuraltube,Shhsignalingstartsinthenotochord.Shhactivates theTFHNF3Binthenotochord.ThisresultsintheproductionofevenmoreShh.At thispoint,thereissomuchShh,thatitbeginstoactivateHNF3Binthefloorplate. This,inturn,resultsinShhbeingproducedbythefloorplate.Hooray!Shhisa morphogen. DrosophilaGastrulation ThisdiagramshowshowgastrulationoccursintheFly.Theimportantconceptwe needtoworryaboutishowcellsdecidetobecomeneuronsorventralepidermis.As youcanseeinfigureIabove,neuroblastsdelaminatefromtheNeuro/Epiregion andmoveclosertothemesoderm.Whereasthecellswhichdonotdelaminate, becomeventralepidermis.ChrisDoedidanexperimentwherehezappednewly formingneuroblastswithalaserjustastheyweredelaminating.Hediscoveredthat whenaneuroblastwaszapped,oneofitstwoneighborswouldbecomeaneuroblast instead.Thisgaverisetotheconceptoflateralinhibition.Lateralinhibitionisthe processbywhichcellsinarowsignaltotheirneighboringcells,regulatingwhich cellswillbecomeneuroblastsandwhichwillbecomeventralepidermis.Lateral inhibitioniscarriedoutbythenotchsystem. EquivalenceGroupAgroupofcellsthatallhavethesamedevelopmental potential.Example:neuroectodermallcellsarecompetent,orcouldgiveriseto neuroblasts.THISDOESNOTMEANTHATALLCELLSWITHINTHEEQUIVALENCE GROUPAREEQUAL. NotchSignaling: Topcellsarestillintugowarstage,"fate"hasnotyetbeendecided.Bottomcells, fatehasbeendecided,leftcellwillbecomeneuroblast,rightcellwillbecomeventral epidermis. Whatsgoingon:InitiallycellsproducebothDelta(ligand)andnotch(receptor).The insideportionofnotchhasacrazylittleguysittingonitcalledSu(H).Whendelta bindstoaNotchreceptor,presenilin(theactiveportionofgammasecretase) cleavesoftheinternalNotch/Su(H)complex.Thiscomplexthengoesdowntothe nucleuswhereit1)turnsoffASC(cannolongerbecomeneural)and2)turnson ventralepidermalgenes.Thecellwillnowbecomeskin.Thecellalsolosesthe abilitytoproduceDelta. ...
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