Presentation on theme: "Embryonic Development"— Presentation transcript:
1 Embryonic Development Timing and coordination of gene activation
2 Genetic Basis of Development Figure 21.8AgendaTurn in your take-home quiz (Place on music stand)Timing and coordination of developmentCytoplasmic Determinants and the maternal effectInduction through cell signalingHomeotic Genes and segment determinationApoptosisScience Skills Practice (Homework if we don’t get to it)“Copy Cat”
3 Cell Division - Morphogenesis –Differentiation Figure 21.4a, bAnimal development. Formation of three germ layers, body cavity, gut, and nervous system.Cells actively migrate during development.Certain cells in each developed tissue remain as partially differentiated stem cells to replace cells that are old or damaged.Plant development. Morphogenesis involves cell division and selective cell expansion. Cells cannot move.The apical meristems located in the roots and shoots remain undifferentiated throughout the plants life for growth.Zygote(fertilized egg)Eight cellsBlastula(cross section)GastrulaAdult animal(sea star)CellmovementGutCell divisionMorphogenesisObservable cell differentiationSeedleavesShootapicalmeristemRootPlantEmbryoinside seedTwo cells(a)(b)
4 Evidence that all cells in a developed organism have all the genetic material Figure 21.6EXPERIMENTResearchers enucleated frog egg cells by exposing them to ultraviolet light, which destroyed the nucleus. Nuclei from cells of embryos up to the tadpole stage were transplanted into the enucleated egg cells.Frog embryoFrog egg cellFrog tadpoleLess differentiated cellDonor nucleusTransplantedEnucleatedegg cellFully differentiated(intestinal) celltransplantedMost developinto tadpoles<2% developWhy are the fully differentiated cells less successful in developing into tadpoles?
5 Timing and coordination of development Cells specialize by activating master control genesWhat is the function of master control genes?DNAOFFmRNAAnother transcription factorMyoDMuscle cell (fully differentiated)MyoD protein (transcription factor)Myoblast (determined)Embryonic precursor cellMyosin, other muscle proteins, and cell-cycle blocking proteinsOther muscle-specific genesMaster control gene myoDNucleus12
6 How do cells know which master control genes to activate during differentiation and morphogenesis? Cytoplasmic Determinants and the maternal effectInduction by cell signaling
7 Induction: Cell signaling changes gene expression Figure 21.11bSignaltransductionpathwayreceptormolecule(inducer)Induction by nearby cells. The cells at the bottom of the early embryo depicted here are releasing chemicals that signal nearby cells to change their gene expression.NUCLEUSEarly embryo(32 cells)Cell signals made by cells early on in in differentiationAffect transcription factors in the nucleus of cells near byChange gene expression of target cell
8 Pattern Formation in Drosophila Translation of bicoid mRNAFertilizationNurse cellsEgg cellbicoid mRNADevelopingegg cellBicoid mRNAin matureunfertilized egg100 µmBicoid protein inearly embryoAnterior end(b) Gradients of bicoid mRNA and Bicoid protein in normal egg and early embryo.123Figure 21.14bBicoid mRNA is placed in the egg cell by nurse cells (maternal effect)There is a gradient of Bicoid mRNA and ProteinWhat experimental evidence suggests that high Bicoid protein concentration causes Anterior (head) segments develop?
9 C. elegans- a model of induction What experimental evidence showed that cell to cell signaling or cell to cell contact between adjacent cells was essential for correct differentiation and morphogenesis?4AnteriorEMBRYOPosteriorReceptorSignalproteindaughtercell of 3Will go on toform muscleand gonadsform adultintestine123Induction of the intestinal precursor cell at the four-cell stage.(a)
10 Cytoplasmic Determinants Figure 21.11aUnfertilized egg cellMolecules of aa cytoplasmicdeterminantFertilizationZygote(fertilized egg)Mitotic cell divisionTwo-celledembryoNucleusmRNA, protein or other signaling molecules in the cytoplasm of the unfertilized eggUnevenly distributedMitosis creates cells with different sets of cytoplasmic determinantsHow might these cytoplasmic determinants regulate gene expression?Molecules ofanother cyto-plasmic deter-minant
11 Homeotic GenesHomeotic genes are regulatory genes that determine where certain anatomical structures, such as appendages, will develop in an organism during morphogenesis.These seem to be the master genes of developmentMutant with legs growing out of headNormalWhat are the functional (protein) products of Homeotic genes that enable them to determine cell fate?What part of the DNA would they interact with?
12 Four general phases for body formation Organize body along major axesOrganize into smaller regions (organs, legs)Cells organize to produce body partsCells themselves change morphologies and become differentiated
13 Programmed Cell Death (Apoptosis) Cell signaling is involved in programmed cell deathIs essential for normal development.2 µmFigure 21.17
14 Apoptosis is essential for morphogenesis of hands and feet Figure 21.19Interdigital tissue1 mm
16 Homeotic Genes and Evolution What is the evidence that homeotic genes are evolutionarily conserved?What does this figure mean? Adultfruit flyFruit fly embryo(10 hours)FlychromosomeMousechromosomesMouse embryo(12 days)Adult mouseFigure 21.23
17 A. Drosophila's eight Hox genes in a single cluster and 39 HOX genes in humans. B. Expression patterns of Hox and HOX genes along the anterior-posterior axis in invertebrates and vertebrates.
18 Hox genes in the Animal Kingdom: increasing numbers and types of Hox genes (animal homeotic genes), increased body plan complexity
19 Hox genes determine the number and types of vertebrae in animals How does homeotic gene regulation help organisms evolve different body plans?Hox genes determine the number and types of vertebrae in animalsHoxc-6 determines that in the chicken the 7 vertebrae will develop into ribsSnake: Hoxc-6 is expanded dramatically toward the head and toward the rear so all these vertebrae develop ribs.
20 Start homework!Science Skills Practice: how do we know enhancers regulate gene expressionScience Skills practice: Hox genes and segment development