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Chapter 21

Chapter 21. The Genetic Basis of Development. Model Organisms. Embryonic Development. Cell Division Cell differentiation Morphogenesis Body plan and body axes Animals: Movements of cells and tissues Plants: Apical meristems. Animal development. Gut. Cell movement. LE 21-4. Zygote

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Chapter 21

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  1. Chapter 21 The Genetic Basis of Development

  2. Model Organisms

  3. Embryonic Development • Cell Division • Cell differentiation • Morphogenesis • Body plan and body axes • Animals: Movements of cells and tissues • Plants: Apical meristems

  4. Animal development Gut Cell movement LE 21-4 Zygote (fertilized egg) Eight cells Blastula (cross section) Gastrula (cross section) Adult animal (sea star) Cell division Morphogenesis Observable cell differentiation Seed leaves Plant development Shoot apical meristem Root apical meristem Two cells Zygote (fertilized egg) Embryo inside seed Plant

  5. Differential Gene Expression • Genomic equivalence? • Totipotency in plants – Fig, 21.5 • Cells dedifferentiated • Dedifferentiation in animal cells? • Cloning

  6. Transverse section of carrot root LE 21-5 2-mg fragments Fragments cul- tured in nutrient medium; stir- ring causes single cells to shear off into liquid. Single cells free in suspension begin to divide. Embryonic plant develops from a cultured single cell. Plantlet is cul- tured on agar medium. Later it is planted in soil. A single somatic (nonreproductive) carrot cell developed into a mature carrot plant. The new plant was a genetic duplicate (clone) of the parent plant. Adult plant

  7. Frog embryo Frog egg cell Frog tadpole UV LE 21-6 Fully differ- entiated (intestinal) cell Less differ- entiated cell Donor nucleus trans- planted Donor nucleus trans- planted Enucleated egg cell Most develop into tadpoles <2% develop into tadpoles

  8. Mammary cell donor Egg cell donor LE 21-7 Egg cell from ovary Nucleus removed Cells fused Cultured mammary cells are semistarved, arresting the cell cycle and causing dedifferentiation Nucleus from mammary cell Grown in culture Early embryo Implanted in uterus of a third sheep Surrogate mother Embryonic development Lamb (“Dolly”) genetically identical to mammary cell donor

  9. Stem Cells in Animals • Stem cells • Embryonic • Totipotent • Adult • Pluripotent stem cells

  10. Embryonic stem cells Adult stem cells LE 21-9 Totipotent cells Pluripotent cells Cultured stem cells Different culture conditions Different types of differentiated cells Liver cells Nerve cells Blood cells

  11. Differentiation • Transcriptional regulation of gene expression during development • Determination and tissue-specific proteins • Master regulatory genes • Cytoplasmic determinants and cell-cell signals • Cytoplasmic determinants • Induction

  12. Nucleus Master control gene myoD Other muscle-specific genes LE 21-10_3 DNA Embryonic precursor cell OFF OFF Determination mRNA OFF MyoD protein (transcription factor) Myoblast (determined) Differentiation mRNA mRNA mRNA mRNA Myosin, other muscle proteins, and cell-cycle blocking proteins MyoD Another transcription factor Muscle cell (fully differentiated)

  13. Unfertilized egg cell Sperm Molecules of another cytoplasmic determinant LE 21-11a Molecules of a cytoplasmic determinant Nucleus Fertilization Zygote (fertilized egg) Mitotic cell division Two-celled embryo Cytoplasmic determinants in the egg

  14. Early embryo (32 cells) LE 21-11b Signal transduction pathway NUCLEUS Signal receptor Signal molecule (inducer) Induction by nearby cells

  15. Pattern Formation • Pattern formation – the body plan • Positional information • Cytoplasmic determinants • Induction

  16. Follicle cell Egg cell developing within ovarian follicle Nucleus Egg cell Nurse cell LE 21-12a Fertilization Laying of egg Fertilized egg Egg shell Nucleus Embryo Multinucleate single cell Early blastoderm Plasma membrane formation Yolk Late blastoderm Body segments Cells of embryo Segmented embryo 0.1 mm

  17. Hatching Larval stages (3) LE 21-12b Pupa Metamorphosis Thorax Head Abdomen Adult fly 0.5 mm Dorsal BODY AXES Anterior Posterior Ventral

  18. LE 21-13 Eye Leg Antenna Wild type Mutant

  19. Cell Signaling: Body Plan • Axis establishment • Maternal effect genes (aka, egg-polarity genes) • Morphogens • Segmentation pattern – genes • Identity of body parts • Homeotic genes (Hox genes) • Apoptosis

  20. Tail Head LE 21-14 Wild-type larva Tail Tail Mutant larva (bicoid) Drosophila larvae with wild-type and bicoid mutant phenotypes Nurse cells Egg cell Developing egg cell bicoid mRNA Bicoid mRNA in mature unfertilized egg Fertilization Translation of bicoid mRNA 100 m m Bicoid protein in early embryo Anterior end Gradients of bicoid mRNA and Bicoid protein in Normal egg and early embryo

  21. Table 21-UN425

  22. Ced-9 protein (active) inhibits Ced-4 activity Mitochondrion LE 21-18 Death signal receptor Ced-4 Ced-3 Inactive proteins No death signal Cell forms blebs Ced-9 (inactive) Death signal Active Ced-4 Active Ced-3 Other proteases Nucleases Activation cascade Death signal

  23. Morphological Diversity • Widespread conservation of developmental genes among animals • Homeobox  homeodomain • Not only present in Hox genes

  24. LE 21-23a Adult fruit fly Fruit fly embryo (10 hours) Fly chromosome

  25. Mouse chromosomes LE 21-23b Mouse embryo (12 days) Adult mouse

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