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U of M BIOLOGY 4361 - Cell-Cell Communication in Development

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Cell-Cell Communication in DevelopmentGeneral Questions:Cell–Cell Communication - TopicsInduction and CompetenceInduction - Vertebrate Eye DevelopmentInduction and CompetenceCompetence FactorsStepwise InductionLens InductionReciprocal InductionMouse Lens – Reciprocal InductionInstructive and Permissive InteractionsInduction Between Epithelia and MesenchymeSkin Epithelium & MesenchymeRegional Specificity of InductionGenetic Specificity of InductionInducing SignalsParacrine Factor FamiliesSignal TransductionRTK PathwayRTK Pathway – Mitf STAT Pathway – Casein GeneHedgehog PathwayWnt PathwaysSMAD PathwayApoptosisApoptosis SignalsJuxtacrine SignalingExtracellular Matrix SignalsMaintaining Differentiation - 1Maintaining Differentiation - 2Maintaining Differentiation - 3Maintaining Differentiation - 4Community EffectCell-Cell Communication in DevelopmentBiology 4361 - Developmental BiologyOctober 9, 2007General Questions:2. How are cell organized into tissues and organs? [Morphogenesis]1. How do cells differentiate? [Differentiation]3. How do cells know when to stop dividing? [Growth]4. How is gametogenesis accomplished? [Reproduction]5. How do changes in development create new body forms? [Evolution]6. How is development of an organism integrated into the larger context of its habitat? [Environmental integration]Cell–Cell Communication - TopicsParacrine factors – inducer moleculesSignal transduction cascadesCell death pathwaysJuxtacrine signalingCross-talk between pathwaysMaintenance of the differentiated stateInduction and competenceInduction and CompetenceCompetence – the ability of a cell or tissue to respond to a specific inductive signal.Induction – interaction at close range between two or more cells or tissues with different histories and properties.Inducer – tissue that produces a signal that changes cellular behavior.Responder – tissue being induced.Development depends on the precise arrangement of tissues and cells.- organ construction is precisely coordinated in time and space- arrangements of cells and tissues change over timeNote – the target tissue must be capable of responding = competenceInduction - Vertebrate Eye DevelopmentLens placode (tissue thickening) induced in head ectodermby close contact with neural (brain) tissueThe developing lens induces brain to form the optic cup(Reciprocal Induction)Induction and CompetencePax6Pax6Competence FactorsCompetence – the ability of a cell or tissue to respond to a specific inductive signal- actively acquired (and can also be transient)During lens induction Pax6 is expressed in the head ectoderm, but not in other regions of surface ectodermPax6 is a competence factor for lens inductionStepwise InductionInducersOften multiple inducer tissues operate on a structure; e.g. for frog lens:-1stinducer - pharyngeal endoderm & heart-forming mesoderm-2ndinducer - anterior neural plate (including signal for ectoderm Pax6 synthesis)Inducers are molecular components; e.g. optic vesicle inducers: - BMP4 (bone morphogenic protein 4)- Fgf8 (fibroblast growth factor 8)- induces Sox2 and Sox3 transcription factors- induces L-Maf transcription factorLens InductionReciprocal InductionABCDMouse Lens – Reciprocal InductionInstructive and Permissive Interactionsa signal from the inducing cell is necessary for initiating new gene expression in the responding cellGeneral principles of instructive interactions:1. In the presence of tissue A, responding tissue B develops in a certain way.2. In the absence of tissue A, responding tissue B does not develop in that way.3. In the absence of tissue A, but in the presence of tissue C, tissue B does not develop in that way.Permissive:- e.g. optic vesicle placed under a new region of head ectoderm- without inducing cell, the responding cell is not capable of differentiating (in that particular way).- tend to restrict the cell’s developmental options- tend to regulate the degree of expression of the remaining developmental potential of the cell.Instructive:the responding tissue has already been specified; needs only an environment that allows the expression of those traits.Induction Between Epithelia and MesenchymeEpithelia – sheets or tubes of connected cells- originates from any cell layerMesenchyme – loosely packed, unconnected cells- derived from mesoderm or neural crestAll organs consist of an epithelium and an associated mesenchyme.Many inductive events involve interactions between epithelia and mesenchyme.Regional specificity of inductionGenetic specificity of inductionGeneral properties of epithelial-mesenchymal inductions:Mesenchyme plays an instructive role – initiating gene activity in responding epithelial cellsSkin Epithelium & MesenchymeEpitheliumMesenchymeinductivesignalsepithelial derivatives:- feathers- hair - mammary glands- scales - sweat glandsRegional Specificity of InductionThe source of the mesenchyme (the inducing tissue) determines the structure of the epithelial derivative.Genetic Specificity of InductionMesenchyme induces epithelial structures -- but can only induce what the epithelium is genetically able to produceInducing SignalsAlso:autocrine (self-generated) signalsendocrine signalsParacrine Factor FamiliesFibroblast growth factor (FGF)Hedgehog familyWingless family (Wnt)TGF-β superfamily (TGF = transforming growth factor)-TGF-β family- Activin family- Bone morphogenic proteins (BMPs)-Vg1 familySignal TransductionInducing signals are transduced at the cell membrane; i.e. an external signal (a paracrine factor or hormone) is transmitted into the interior of the cell= hormone or paracrine factorautophosphorylationintracellularsignale.g. receptor tyrosine kinase (RTK)(kinase = protein phosphorylating enzyme)receptorspansmembraneligand binding = conformational changeRTK Pathway2. RTK dimerized1. ligand binding3. RTK phosphorylation4. adaptor protein binding5. GNRP binding6. GNRP activates Ras(G protein)7. Ras-GDP → Ras-GTP(8. GAP recycles Ras)9. active Ras activates Raf(protein kinase C)10. Raf phosphorylates MEK11. MEK phosphorylates ERK (a kinase)12. ERK phosphorylatestranscription factors13. transcription activatesRTK Pathway – MitfStem cell factor (a paracrine factor) stimulates genes needed for melanocyte production.STAT Pathway – Casein GeneHedgehog PathwayWnt Pathwayscanonical Wnt pathwaySMAD PathwayApoptosisApoptosis – programmed cell deathe.g. - embryonic neural growth- embryonic brain produces 3X neurons found at birth - hand


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U of M BIOLOGY 4361 - Cell-Cell Communication in Development

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