4/5/15%1%What%makes%cells%different?%1. Understand%that%differences%in%gene%expression%are%a%result%of%a%sequence%of%events%that%occur%as%cells%divide%and%process%signals.%2. Know%that%these%events%result%in%both%transient%and%heritable%acDvaDon%(or%inacDvaDon)%of%specific%subsets%of%genes%(cellular%memory).%3. Know%the%two%kinds%of%events%that%influence%gene%expression:%cytoplasmic%events%(cellLautonomous;%intrinsic)%and%cellLcell%signaling%events%(cellLcell%interacDon,%cellLnonLautonomous;%extrinsic).%4. Understand%how%morphogen%gradients%act%to%determine%cell%fates.%Fate%mapping%in%chick%embryo%Learning%goals:%Wednesday:%%More%acDve%learning.%Students%learn%beSer%when%they%are%already%familiar%with%basic%concepts%prior%to%class%Dme.%%But%it%is%also%clear%the%students%don’t%like%to%do%this.%%So%to%encourage%you%to%read%I’m%going%to%give%you%onLline%quizzes%for%the%next%two%class%periods%–%these%count%for%2%%of%your%final%grade.%%1) Read%the%assigned%material%(on%the%last%slide%today)%2) Go%to%Blackboard%and%take%the%short%quiz%on%the%material.%3) Get%5%out%of%the%eight%quesDons%right%and%get%full%credit%for%the%quiz.%%Less%than%5%–%no%credit.%4) Come%to%class%prepared%to%think%and%communicate.%4/5/15%2%Fer$liza$on+Cleavage+ Gastrula$on+ Neurula$on+ Organogenesis+zygote+blastomere+blastula+Cell%shape%changes%Cell%growth%Central%quesDons%in%Developmental%Biology:%1. How+do+different+cells+come+to+express+different+genes?++Developmental+events+and+gene+regula$on+(L17F19)+2. How+do+cells+come+to+be+different+in+an+organized+and+reproducible+way?+Regional+Specifica$on/Axis+forma$on+(L20F23)+3. How+do+cells+organize+into+$ssues+and+organs?++Morphogenesis+(L20F22)+4. How+do+similar+cells+organize+into+different+shapes+and+paUerns?++PaUern+forma$on+(L23)+5. How+do+organisms+maintain+$ssues+and+organs?+Stem+cells+(L24)+Germ+layers:+Ectoderm+Endoderm+Mesoderm+Describe%Perturb%%experimental%%geneDc%Central%quesDons%in%Developmental%Biology:%%1. How+do+different+cells+come+to+express+different+genes?++2. How+do+cells+come+to+be +diffe r e nt+in+an+organized+and+reproducible+way?+3. How+do+cells+organize+into+$ ssue s+and+organs?++4. How+do+similar+cells+organiz e +into+different+shapes+and+paUerns?++5. How+do+organisms+maintain+$ssues+and+organs?++4/5/15%3%What%makes%cells%different?%411%cell%types%in%humans%Review%DifferenDal%Gene%expression%%Describing%Development:%how%can%we%know%the%fate%of%a%cell?%%lineage%tracing%%%fate%mapping%%How%are%cell%fates%specified?%%DeterminaDon%vs.%DifferenDaDon%%Two%mechanisms%by%which%cells%become%determined%%Cell%autonomous%determinaDon%%CondiDonal%determinaDon%%%inducDon%%%morphogen%gradients%%%%%4/5/15%4%Differen$al+Gene+Expression:%%• %%All%cells%in%an%organism%have%the%same%DNA%sequence.%• %%Different%cells%express%different%subsets%of%genes.%• %%Cells%“remember”%their%idenDty.%%%Two+components+of+differen$al+gene+expression:+%What%is%the%nature%of%the%switches%that%turn%genes%on%or%off%and%keep%them%on%or%off?%%What%are%the%events%that%turn%parDcular%switches%on%or%off?%%%%Developmental%events:%%Asymmetric%divisions%%%(Localized%cytoplasmic%determinants)%%Cell%signaling%%Morphogen%gradients%TranscripDonal%and%posSranscripDonal%controls%%4/5/15%5%What%are%the%developmental%events%that%cause%cells%to%be%different?%Start%with%descripDon%of%development:%%Which%of%the%embryonic%blastomeres%gives%rise%to%which%cell%types?%%In%other%words,%for%a%given%early%embryonic%blastomere,%what%is%its%Developmental+Fate%or%Cell+Fate?%Review%DifferenDal%Gene%expression%%Describing%Development:%how%can%we%know%the%fate%of%a%cell?%%lineage%tracing%%%fate%mapping%%How%are%cell%fates%specified?%%DeterminaDon%vs.%DifferenDaDon%%Two%mechanisms%by%which%cells%become%determined%%Cell%autonomous%determinaDon%%CondiDonal%determinaDon%%%inducDon%%%morphogen%gradients%%%%%4/5/15%6%Cell%lineage%tracing%AB%P1%ABa%ABp%EMS%P2%How%do%we%know%the%developmental%fate%of%a%cell?%%%Molecular%Biology%of%the%Cell,%Figure%22L18%Cell%lineage%of%the%nematode%C.#elegans#4/5/15%7%Could%you%determine%the%complete%cell%lineage%of%a%frog%embryo?%%Frog%blastula%Frog%blastula%How%do%we%know%the%developmental%fate%of%a%cell%when%a%complete%cell%lineage%is%not%possible?%Fate+mapping+4/5/15%8%To%derive%a%fate%map,%mulDple%experiments%are%required.%Dye%injecDons%can%be%used%for%fate%mapping.%Fate%map%of%the%frog%at%the%beginning%of%gastrulaDon%4/5/15%9%%%%%%%How%do%we%know%the%developmental%fate%of%a%cell?%%Cell%lineage%tracing%%%%%%%%%%%%%%%%%%or % %%%%fate%mapping%C.#elegans%cell%lineage% Fate%map%of%frog%at%gastrulaDon%What%is%the%value%of%a%fate%map?%4/5/15%10%Review%DifferenDal%Gene%expression%%Describing%Development:%how%can%we%know%the%fate%of%a%cell?%%lineage%tracing%%%fate%mapping%%How%are%cell%fates%specified?%%DeterminaDon%vs.%DifferenDaDon%%Two%mechanisms%by%which%cells%become%determined%%Cell%autonomous%determinaDon%%CondiDonal%determinaDon%%%inducDon%%%morphogen%gradients%%%%%4/5/15%11%Decisions%about%cell%fate%are,%for%the%most%part,%irreversible%and%occur%in%two%steps:%Differen$a$on:%the%process%of%expressing%cellLtype%specific%characters.%%(Second%step)%%Determina$on:%%Cells%become%commiSed%irreversibly%to%a%parDcular%developmental%fate.%%DeterminaDon%typically%precedes%overt%differenDaDon.%%(First%step)%Molecular%Biology%of%the%Cell,%Figure%22L7%Opera$onal+defini$on+of+determina$on:+%TransplantaDon%of%cells%from%their%normal%posiDon%to%a%new%posiDon%in%the%embryo%does%not%change%their%normal%fate.%%4/5/15%12%Commitment%to%a%parDcular%cell%fate%is%progressive.%Cells%have%memory!%Ectoderm+vs.+endoderm+vs.+mesoderm +ventral+++vs.+++dorsal + +notochord+++++vs.+++++intermediate+mesoderm++++ +back+muscle+++++++++vs.+++++++++heart
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