ta notes week 2

ta notes week 2 - BIPN144Week2Notes(part1)

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Unformatted text preview: BIPN144Week2Notes(part1) Note:ThishasnotbeenreviewedbyDr.Bierandmayhaveerrors.Always trusttheprofessoroverthesenotes. Brieflyreviewedregulatoryregion/codingregion Dr.Bierintroduced2importantkindsofMolecules: 1)Signalsusuallyaprotein(sometimesasmallcompoundlikeRetinoicAcid,but notinthisclass)whichissecreted,itthendiffusesandbindstoreceptorsand triggersaresponse. Sometimessignalsareboundtothemembranesofthecellsthatproducethem, howeverwehaven'treallycoveredtheseinclassyet,justbeawarethattheyexist SeeFigure18 2)TranscriptionFactors(TF's)AproteinthatbindstoDNAintheregulatory regionandeitheractivates(inwhichcaseitiscalledanactivator)orrepresses(in whichcaseitiscalledarepressor)theprocessoftranscription.TF'scanbesequence specific,bindingonlytoaspecificsequenceofDNA Inadditiontothesetwoimportanttypesofmolecules,DrBierintroducedtheKey ConceptofaMorphogen. Morphogenakindofsignalthatis: 1) producedbyonegroupofcellsanddiffusestocellshatdonotproduceit 2) Itisdistributedinagradedfashion(havinganadjacentsourceandsinkthe sinkeliminatesittherebymaintainingupascenariowherecellsclosestto thesourceexperienceahigherconcentration,whiledistantcellsgetlessor none) Seefigure19 3) Differentconcentrationsofmorphogenelicitdifferent(distinct)responses. Mostcommonly,morphogenselicit3differentconcentrationdependent responses,howeversomemorphogenshaveupto5possibleresponsesand someonly2). InresponsetoaquestionDrBierdefinedthetermgradient Gradientmoleculepresentinagradedfashion DrBierthenintroducedustoavisualdepictionofaflyembryo(figure1.6inthetext book).Andthenbrieflydescribedthegermlayers: 1) Ectoderm(outerlayer)formsepidermisandNS 2) Mesoderm(middlelayer)formsmuscle,bloodandfat 3) Endoderm(innerlayer)formsthegut Thiscanbealittleconfusingbecauseintheearlieststages,theflyembryois organizedmoreintolevels,likestoriesofabuilding.Thegermlayersdonotassume theirouter,middle,andinnerrelativelocationsuntillateronindevelopment. Wethentookacloserlookattheflyembryoinearlydevelopmentandtheeffectsof aspecialmorphogen(andTF)calledDorsal.SeeFigure37A (Note:DorsalisnotatypicalMorphogen. Asmentionedabove,DorsalisbothaTFandamorphogen.Dorsalisalocalized maternalfactor,meaningitisproducedonlyundercontrolofthemother. (AsopposedtoZygoticgenes,whicharetheembryosowngenesthatgetactivated bymaternalfactors). Dorsalhas3majorresponsesitactivatesgenesineachofthethreeregionsthatwill becomethegermlayers.Astudentaskedwhyitwascalleddorsalwhenitis obviouslyaventralizingfactor.Theanswerwashatgenesareoftennamedforthe effectoftheirabsence.Inthiscase,mutantsthathavenodorsaldisplayonlythe uppermost(ordorsal)germlayer.Thiscanbeconfusing.Sorry. DrBierthenwentthroughtheembryolayerbylayertoexplainwhatwasgoingon, beginningwiththeMesoderm(Redinaboveimage)whichreceivesthehighest concentrationofDorsal. 1)HighConcentrationofDorsal ActivatesTwistTwistisanactivatorofMesodermgenes ActivatesSnailSnailisarepressorofNeuralgenes,andthereforestops tissuefrombecomingneuraltissue 2)MidlevelsofDorsal ActivatesBrinker(Brk)repressesepidermalgenes ASCgenesareactiveTF'sthatactivateneuralgenes o ASCgenesarenotdependentondorsalforactivation,howeverthey orenotexpressedinothergermlayersbecauseinothergermlayers theyareactivelyrepressed ActivatesSOGasignalwhichrepressesDPP Rhomboid(Rho)alsoactiveinthisregion,producesventralskin.Don't worrymuchaboutthis. 3)LowtoNoDorsal ActivatesDPPasignalwhich: o ActivatesEpidermalgenes o RepressesNeuralgenes o (alsoappearstoreinforceitsownexpressionpositivefeedback) ...
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