Bài giảng Biology - Chapter 19: Cellular Mechanismsof Development

Cellular Mechanismsof DevelopmentChapter 191Overview of DevelopmentDevelopment is the successive process of systematic gene-directed changes throughout an organism’s life cycle -Can be divided into four subprocesses: -Growth (cell division) -Differentiation -Pattern formation -Morphogenesis2Cell DivisionAfter fertilization, the diploid zygote undergoes a period of rapid mitotic divisions -In animals, this period is called cleavage -Controlled by cyclins and cyclin- dependent kinases (Cdks)During cleavage, the zygote is divided into smaller & smaller cells called blastomeres -Moreover, the G1 and G2 phases are shortened or eliminated3Cell Division4Cell DivisionCyclinDegradationCMG2interphasemitosiscytokinesisG2SG1MCMitosisDNA SynthesisAdult Cell CycleSG1 Cdk /G1cyclinCdk /S cyclinMitosisDNA SynthesisActiveCell Cycle of Early Frog BlastomereActiveActiveCyclinSynthesisActive Cdk /G2cyclinCMSSMCdk /cyclinCdkInactivea.b.5Cell DivisionCaenorhabditis elegans -One of the best developmental models -Adult worm consists of 959 somatic cells -Transparent, so cell division can be followed -Researchers have mapped out the lineage of all cells derived from the fertilized egg6Nematode Lineage Mapa.b.Egg andsperm lineEggPharynxCuticle-making cellsVulvaEggSpermAdult NematodeVulvaGonadGonadGonadNervous systemPharynxIntestineCuticleIntestineNervoussystemCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.7Cell DivisionBlastomeres are nondifferentiated and can give rise to any tissueStem cells are set aside and will continue to divide while remaining undifferentiated -Tissue-specific: can give rise to only one tissue -Pluripotent: can give rise to multiple different cell types -Totipotent: can give rise to any cell type8Cell DivisionCleave in mammals continues for 5-6 days producing a ball of cells, the blastocyst -Consists of: -Outer layer = Forms the placenta -Inner cell mass = Forms the embryo -Source of embryonic stem cells (ES cells)9EggSpermBlastocystEmbryoEmbryonic stem-cellcultureInner cellmassOnce sperm cell and egg cell have joined, cellcleavage produces a blastocyst. The inner cell massof the blastocyst develops into the human embryo.Embryonic stem cells (ES cells) areisolated from the inner cell mass10Cell DivisionA plant develops by building its body outward -Creates new parts from stem cells contained in structures called meristems -Meristematic stem cells continually divide -Produce cells that can differentiate into the various plant tissues -Leaves, roots, branches, and flowersThe plant cell cycle is also regulated by cyclins and cyclin-dependent kinases11Cell DifferentiationA human body contains more than 210 major types of differentiated cellsCell determination commits a cell to a particular developmental pathway -Can only be “seen” by experiment -Cells are moved to a different location in the embryo -If they develop according to their new position, they are not determined12DonorNo donorRecipientBefore OvertDifferentiationRecipientAfter OvertDifferentiationNormalNot Determined(early development)Determined(later development)Tail cells aretransplantedto headTail cells developinto head cells in headTail cells developinto tail cells in headTail cells aretransplantedto headTailHeadCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.13Cell DifferentiationCells initiate developmental changes by using transcriptional factors to change patterns of gene expressionCells become committed to follow a particular developmental pathway in one of two ways: 1) via differential inheritance of cytoplasmic determinants 2) via cell-cell interactions14Cell DifferentiationCytoplasmic determinants -Tunicates are marine invertebrates -Tadpoles have tails, which are lost during metamorphosis into the adult -Egg contains yellow pigment granules -Become asymmetrically localized following fertilization -Cells that inherit them form muscles 15Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.a.n2nEmbryo(diploid) 2nLarva(diploid) 2nSperm(haploid) nEgg(haploid) nPigmentgranulesAdult tunicate(diploid) 2nMEIOSISMEIOSISMETAMORPHOSIS16Cell DifferentiationCytoplasmic determinants -Female parent provides egg with macho-1 mRNA -Encodes a transcription factor that can activate expression of muscle- specific genes17Cell DifferentiationInduction is the change in the fate of a cell due to interaction with an adjacent cellIf cells of a frog embryo are separated: -One pole (“animal pole”) forms ectoderm -Other pole (“vegetal pole”) forms endoderm -No mesoderm is formedIf the two pole cells are placed side-by-side, some animal-pole cells form the mesoderm 18Cell DifferentiationAnother example of induction is the formation of notochord and mesenchyme in tunicates -Arise from mesodermal cells that form at the vegetal margin of 32-cell stage embryo -Cells receive a chemical signal from underlying endodermal cells -Anterior cells differentiate into notochord -Posterior cells differentiate into mesenchyme19AnteriorPosteriorAnteriorPosteriora.b.c.21FGF signalingSagittal sectionLongitudinal sectionLongitudinal sectionDorsal nerve cord (NC)Mesenchymal cells (Mes)Tail muscle cells (Mus)32-Cell Stage64-Cell StageAnteriorPosterior21Notochord (Not)Ventral endoderm (En)Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.20Cell DifferentiationThe chemical signal is a fibroblast growth factor (FGF) molecule -The FGF receptor is a tyrosine kinase that activates a MAP kinase cascade -Produces a transcription factor that triggers differentiationThus, the combination of macho-1 and FGF signaling leads to four different cell types21Cell Differentiationa.FGF Signal received?MesenchymeMuscleNotochordFGF Signal received?Macho-1 inherited?Nerve cordFirst StepCell TypesSecond StepYesNoYesNoYesNoFGFFGF ReceptorRas/MAPKPathwayT-EtsMacho-1Cell membranePMesenchymePrecursor CellsSuppression of musclegenes and activationof mesenchyme genesb.22Cell DifferentiationNoFGFFGF ReceptorRas/MAPKPathwayT-EtsCell membraneNerve cordPrecursor CellsFGFFGF ReceptorTranscriptionof notochord genesPNotochord Precursor CellsNoFGFFGF ReceptorRas/MAPKPathwayTranscription of muscle genesMusclePrecursor Cells Suppression of notochordgenes and activationof nerve cord genesNo Macho-1No Macho-1Macho-1Cell membraneCell membraneT-EtsT-EtsRas/MAPKPathway23CloningUntil very recently, biologists thought that determination and cell differentiation were irreversible in animalsNuclear transplant experiments in mammals were attempted without success -Finally, in 1996 a breakthrough Geneticists at the Roslin Institute in Scotland performed the following procedure:24Cloning1. Differentiated mammary cells were removed from the udder of a six-year old sheep2. Eggs obtained from a ewe were enucleated3. Cells were synchronized to a resting state4. The mammary and egg cells were combined by somatic cell nuclear transfer (SCNT)5. Successful embryos (29/277) were placed in surrogate mother sheep6. On July 5, 1996, Dolly was born25DevelopmentImplantationBirth of CloneGrowth to AdulthoodEmbryo begins todevelop in vitro.Embryo isimplanted intosurrogatemother.After a five-month pregnancy, alamb genetically identical to thesheep from which the mammarycell was extracted is born.EmbryoPreparationCell FusionCell DivisionMammary cell is extracted and grown in nutrient-deficient solution that arrests the cell cycle.Egg cell is extracted.Nucleus is removed fromegg cell with a micropipette.Nucleus containingsource Mammary cell isinserted insidecovering of egg cell.Electric shock fuses cellmembranes and triggerscell division.26CloningDolly proved that determination in animals is reversible -Nucleus of a differentiated cell can be reprogrammed to be totipotentReproductive cloning refers to the use of SCNT to create an animal that is genetically identical to another -Scientists have cloned cats, rabbits, rats, mice, goats and pigs27CloningReproductive cloning has inherent problems 1. Low success rate 2. Age-associated diseasesNormal mammalian development requires precise genomic imprinting -The differential expression of genes based on parental originCloning fails because there is not enough time to reprogram the genome properly28CloningIn therapeutic cloning, stem cells are cloned from a person’s own tissues and so the body readily accepts them Initial stages are the same as those of reproductive cloning -Embryo is broken apart and its embryonic stem cells extracted -Grown in culture and then used to replace diseased or injured tissue29CloningThe skin cellnucleus is insertedinto the enucleatedhuman egg cell.Cell cleavageoccurs as theembryo begins todevelop in vitro.The embryoreaches theblastocyst stageThe nucleus from a skin cell of a diabeticpatient is removed.The nucleus from a skin cell of a healthy patient is removed.Early embryoBlastocystInner cellmassEScellsDiabeticpatientHealthypatient30CloningTherapeutic CloningReproductive CloningEmbryonic stem cells(ES cells) are extractedand grown in culture.The blastocyst is kept intact andis implanted into the uterus of asurrogate mother.The resulting baby isa clone of thehealthy patient.The stem cells are developedinto healthy pancreatic islet cellsneeded by the patient.The healthy tissue isinjected or transplantedinto the diabetic patient.Healthy pancreatic islet cellsDiabeticpatient31CloningHuman embryonic stem cells have enormous promise for treating a wide range of diseases -However, stem cell research has raised profound ethical issues Very few countries have permissive policy towards human reproductive cloning -However, many permit embryonic stem cell research32CloningEarly reports on a variety of adult stem cells indicated that they may be pluripotent -Since then these results have been challenged33Pattern FormationIn the early stages of pattern formation, two perpendicular axes are established -Anterior/posterior (A/P, head-to-tail) axis -Dorsal/ventral (D/V, back-to-front) axisPolarity refers to the acquisition of axial differences in developing structuresPosition information leads to changes in gene activity, and thus cells adopt a fate appropriate for their location34Drosophila EmbryogenesisDrosophila produces two body forms -Larva – Tubular eating machine -Adult – Flying sex machine axes are establishedMetamorphosis is the passage from one body form to anotherEmbryogenesis is the formation of a larva from a fertilized egg35Drosophila EmbryogenesisBefore fertilization, specialized nurse cells move maternal mRNAs into maturing oocyte -These mRNA will initiate a cascade of gene activations following fertilizationEmbryonic nuclei do not begin to function until approximately 10 nuclear divisions later36Drosophila EmbryogenesisAfter fertilization, 12 rounds of nuclear division without cytokinesis produces a syncytial blastoderm -4000 nuclei in a single cytoplasmMembranes grow between the nuclei forming the cellular blastodermWithin a day of fertilization, a segmented, tubular body is formed37c.b.NursecellsAnteriorPosteriorMovement ofmaternal mRNAOocyteFolliclecellsFertilized egga.d.e.Three larval stagesSyncytial blastodermCellular blastodermNuclei line up alongsurface, and membranesgrow between them toform a cellular blastoderm.Segmented embryo prior to hatchingMetamorphosisAbdomenThoraxHeadHatching larvaCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.NucleusEmbryo38Drosophila EmbryogenesisNüsslein-Volhard and Wieschaus elucidated how the segmentation pattern is formed -Earned the 1995 Nobel PrizeTwo different genetic pathways control the establishment of the A/P and D/V polarity -Both involve gradients of morphogens -Soluble signal molecules that can specify different cell fates along an axis39About 21/2 hours after fertilization, bicoid protein turns on a series of brief signals from so-called gap genes. The gap proteins act to divide the embryo into large blocks. In this photo, fluorescent dyes in antibodies that bind to the gap proteins Krüppel (orange) and Hunchback (green) make the blocks visible; the region of overlap is yellow.Forming the SegmentsLaying Down the Fundamental RegionsSetting the Stage for SegmentationBicoidHairyKrüppelHunchbackEngrailedEstablishing the Polarity of the EmbryoCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Fertilization of the egg triggers the production of bicoid protein from maternal RNA in the egg. The bicoid protein diffuses through the egg, forming a gradient. This gradient determines the polarity of the embryo, with the head and thorax developing in the zone of high concentration (green fluorescent dye in antibodies that bind bicoid protein allows visualization of the gradient).About 0.5 hr later, the gap genes switch on the “pair-rule” genes, which are each expressed in seven stripes. This is shown for the pair-rule gene hairy . Some pair-rule genes are only required for even-numbered segments while others are only required for odd numbered segments.The final stage of segmentation occurs when a “segment- polarity” gene called engrailed divides each of the seven regions into halves, producing 14 narrow compartments. Each compartment corresponds to one segment of the future body. There are three head segments (H, bottom right), three thoracic segments (T, upper right), and eight abdominal segments (A, from top right to bottom left).40Establishment of the A/P axisNurse cells secrete maternally produced bicoid and nanos mRNAs into the oocyte -Differentially transported by microtubules to opposite poles of the oocyte -bicoid mRNA to the future anterior pole -nanos mRNA to the future posterior pole -After fertilization, translation will create opposing gradients of Bicoid and Nanos proteins41a.b.bicoid mRNA movestoward anterior endbicoidmRNAMovement ofmaternal mRNANucleusMicrotubulesNursecellsFolliclecellsnanos mRNA movestoward posterior endPosteriorAnteriorPosteriorAnteriornanosmRNACopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.42Establishment of the A/P axisBicoid and Nanos control translation of two other maternal mRNAs, hunchback and caudal, that encode transcription factors -Hunchback activates anterior structures -Caudal activates posterior structuresThe two mRNAs are not evenly distributed -Bicoid inhibits caudal mRNA translation -Nanos inhibits hunchback mRNA translation43ConcentrationAnteriorAnteriora. Oocyte mRNAsc. Early cleavage embryo proteinsb. After fertilizationPosteriorPosteriornanos mRNAhunchback mRNAbicoid mRNAcaudal mRNANanos proteinHunchback proteinBicoid proteinCaudal proteinConcentrationAnteriorPosteriornanos mRNAhunchback mRNAbicoid mRNAcaudal mRNANanos proteinHunchback proteinBicoid proteinCaudal proteinCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.44Establishment of the D/V axisMaternally produced dorsal mRNA is placed into the oocyte -Not asymmetrically localizedOocyte nucleus synthesizes gurken mRNA -Accumulates in a crescent on the future dorsal side of embryoAfter fertilization, a series of steps results in selected transport of Dorsal into ventral nuclei, thus forming a D/V gradient4546Production of Body PlanThe body plan is produced by sequential activation of three classes of segmentation genes 1. Gap genes -Map out the coarsest subdivision along the A/P axis -All 9 genes encode transcription factors that activate the next gene class47Production of Body Plan 2. Pair-rule genes -Divide the embryo into seven zones -The 8 or more genes encode transcription factors that regulate each other, and activate the next gene class 3. Segment polarity genes -Finish defining the embryonic segments48Production of Body PlanSegment identity arises from the action of homeotic genes -Mutations in them lead to the appearance of normal body parts in unusual places -Ultrabithorax mutants produce an extra pair of wings49Production of Body PlanHomeotic gene complexes -The HOM complex genes of Drosophila are grouped into two clusters -Antennapedia complex, which governs the anterior end of the fly -Bithorax complex, which governs the posterior end of the fly -Interestingly, the order of genes mirrors the order of the body parts they control 50Production of Body PlanHomeotic gene complexes -All of these genes contain a conserved 180-base sequence, the homeobox -Encodes a 60-amino acid DNA-binding domain, the homeodomain -Homeobox-containing genes are termed Hox genes -Vertebrates have 4 Hox gene clusters51Production of Body PlanDrosophila HOM genesThoraxAntennapedia complexHeadAbdomenBithorax complexFruit flyFruit flyembryoMouseHox 1Hox 2Hox 3Hox 4Mouseembryoa.b.Drosophila HOM ChromosomesMouse Hox ChromosomeslabpbDfdScrAntpUbxabd-Aabd-B52Pattern Formation in PlantsThe predominant homeotic gene family in plants is the MADS-box genes -Found in most eukaryotic organisms, although in much higher numbers in plantsMADS-box genes encode transcriptional regulators, which control various processes: -Transition from vegetative to reproductive growth, root development and floral organ identity53MorphogenesisMorphogenesis is the formation of ordered form and structure -Animals achieve it through changes in: -Cell division -Cell shape and size -Cell death -Cell migration -Plants use these except for cell migration54MorphogenesisCell division -The orientation of the mitotic spindle determines the plane of cell division in eukaryotic cells -If spindle is centrally located, two equal-sized daughter cells will result -If spindle is off to one side, two unequal daughter cells will result55MorphogenesisCell shape and size -In animals, cell differentiation is accomplished by profound changes in cell size and shape -Nerve cells develop long processes called axons -Skeletal muscles cells are large and multinucleated56MorphogenesisCell death -Necrosis is accidental cell death -Apoptosis is programmed cell death -Is required for normal development in all animals -“Death program” pathway consists of: -Activator, inhibitor and apoptotic protease57a.b.InhibitorCED-9Bcl-2CED-4Apaf1Caspase-8 or -9ApoptosisCED-3ApoptosisInhibitor:Activator:ApoptoticProtease:Caenorhabditis elegansMammalian CellOrganismInhibitionActivationCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.58MorphogenesisCell migration -Cell movement involves both adhesion and loss of adhesion between cells and substrate -Cell-to-cell interactions are often mediated through cadherins -Cell-to-substrate interactions often involve complexes between integrins and the extracellular matrix (ECM)59Development of Seed PlantsPlant development occurs in five main stages:1. Early embryonic cell division -First division is off-center -Smaller cell divides to form the embryo -Larger cell divides to form suspensor -Cells near it ultimately form the root -Cells on the other end, form the shoot60Development of Seed Plants2. Embryonic tissue formation -Three basic tissues differentiate: -Epidermal, ground and vascular3. Seed formation -1-2 cotyledons form -Development is arrested4. Seed germination -Development resumes -Roots extend down, and shoots up61Development of Seed Plants5. Meristematic development and morphogenesis -Apical meristems at the root and shoot tips generate a large numbers of cells -Form leaves, flowers and all other components of the mature plant62a. Early cell divisionEmbryoEmbryoSuspensorb. Tissue formationd. Germinationc. Seed formation meristemSeed wallShoot apicalmeristemRoot apicalShoot apical meristemCotyledonse. Meristematic development and morphogenesisRoot apicalmeristemEpidermalcellsGroundtissue cellsVasculartissue cellsCotyledonsCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.63Environmental EffectsBoth plant and animal development are affected by environmental factors -Germination of a dormant seed proceeds only under favorable soil and day conditions -Reptiles have a temperature-dependent sex determination (TSD) mechanism -The water flea Daphnia changes its shape after encountering a predatory fly larva 64Environmental Effects65Environmental EffectsIn mammals, embryonic and fetal development have a longer time course -Thus they are more subject to the effects of environmental contaminants, and blood-borne agents in the mother -Thalidomide, a sedative drug -Many pregnant women who took it had children with limb defects66Environmental EffectsEndocrine disrupting chemicals (EDCs) -Interfere with synthesis, transport or receptor-binding of endogenous hormones -Derived from three main sources -Industrial wastes (polychlorinated biphenyls or PCBs) -Agricultural practices (DDT) -Effluent of sewage-treatment plants67