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Animal Development

Animal Development. Ch. 47 Mechanisms of Morphogenesis and cell Fate. Mechanisms of Morphogenesis. Cell movement in Morphogenesis Only animals experience cell movement Cytoskeleton plays a large role

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Animal Development

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  1. Animal Development Ch. 47 Mechanisms of Morphogenesis and cell Fate

  2. Mechanisms of Morphogenesis • Cell movement in Morphogenesis • Only animals experience cell movement • Cytoskeleton plays a large role cells crawl within embryo using cytoskeletal fibers to extend and retract cellular protrusions Like amoeboid movement Cell adhesion molecules and ECM are involved

  3. Ectoderm Figure 47.15-5 Neuralplate Microtubules Actinfilaments Neural tube

  4. Figure 47.16 Convergence Extension

  5. Mechanisms of Morphogenesis • Apoptosis- programed cell death • example: tails cells in humans • example: inner digit cells

  6. Cell Fate Specification • Determination- cell or group of cells become committed to a particular fate • Differentiation is the resulting specialization • All cells have the same genes just a matter of gene expression • HHMI Embryonic Stem Cells and Cell Fate • http://www.hhmi.org/biointeractive/creating-embryonic-stem-cell-lines

  7. Cell Fate Specification • Fate maps- diagrams showing the structures from each region of the embryo

  8. Epidermis Epidermis Figure 47.17 Centralnervoussystem Notochord Mesoderm Endoderm Blastula Neural tube stage(transverse section) (a) Fate map of a frog embryo 64-cell embryos Blastomeresinjected with dye Larvae (b) Cell lineage analysis in a tunicate

  9. Cell Fate Specification • Fate maps- diagrams showing the structures from each region of the embryo • Example axis formation • bilateral symmetry • gray crescent is the future dorsal side (opposite sperm entry) • different genes are expressed because different aprts are exposed to different environment

  10. Dorsal Figure 47.21 Right Anterior Posterior Left Ventral (a) The three axes of the fully developed embryo First cleavage Animal pole Pigmentedcortex Animalhemisphere Point ofspermnucleusentry Futuredorsalside Vegetalhemisphere Gray crescent Vegetal pole (b) Establishing the axes

  11. 2 1a 1b Figure 47.22-2 EXPERIMENT Control egg(dorsal view) Experimental egg(side view) Experimentalgroup Controlgroup Graycrescent Graycrescent Thread RESULTS Normal Belly piece Normal

  12. Can Cell Fate Be Modified? • Development potential- what it can become • First two cells are totipotent- can become a new organism • Mammals are totipotent to 8 cells • 16 cells to trophoblast or (inner cell mass) cells are not totipotent but nuclei are • These cells would be pluripotent; can become almost any cell (can’t become the placenta)

  13. Cell Fate Induction • “Organizer” inactivate BM4 (bone morphogenic protein) on dorsal side • Positional information and pattern formation relate to molecular signaling

  14. Formation of Vertebrate Limbs • Apical ectodermal ridge (AER) regulates limb bud development by secreting proteins that signal fibroblast growth factor (FGF). • Zone of polarizing activity (ZPA) regulates limb buds development by secreting a protein growth factor Sonic Hedgehog. • Cells nearest the ZPA give rise to posterior structures. • Hox genes determine if front or hind limbs

  15. Figure 47.24 Anterior Limb bud AER ZPA Limb buds 2 Posterior 50 m Digits Apicalectodermalridge (AER) 3 4 Anterior Ventral Proximal Distal Dorsal Posterior (a) Organizer regions (b) Wing of chick embryo

  16. EXPERIMENT Figure 47.25 Anterior New ZPA Donorlimbbud Hostlimbbud ZPA Posterior RESULTS 4 3 2 2 3 4

  17. Formation of Vertebrate Limbs • Sonic hedgehog is a ligand (protein) that diffuses to form a concentration gradient and has different effects on cells of the developing embryo depending on its concentration. • SSH remains important in the adult. It controls cell division of adult stem cells and has been implicated in development of some cancers.

  18. Cilia and cell fate • Monocilia • Stationary single projections on nearly all animal cells • A19cts as antenna on cell surface to receive signals from multiple proteins

  19. MOST IMPORTANT TO REMEMBER • PRODUCTS OF GENES ALLOW CELLS TO SPECIALIZE

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