1. ANIMAL DEVELOPMENT CH. 47 MECHANISMS OF MORPHOGENESIS AND CELL FATE 1

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 2

3. FIGURE 47.15-5 Ectoderm Neural plate Microtubules Actin filaments Neural tube 3

4. FIGURE 47.16 Extension Convergence 4

5. MECHANISMS OF MORPHOGENESIS Apoptosis- programed cell death example: tails cells in humans example: inner digit cells 5

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 6

7. CELL FATE SPECIFICATION Fate maps- diagrams showing the structures from each region of the embryo 7

8. FIGURE 47.17 Epidermis Central nervous system Notochord Mesoderm Endoderm BlastulaNeural tube stage (transverse section) (a) Fate map of a frog embryo 64-cell embryos Blastomeres injected with dye Larvae (b) Cell lineage analysis in a tunicate 8

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 9

10. FIGURE 47.21 Dorsal Right AnteriorPosterior Ventral Left (a) The three axes of the fully developed embryo (b) Establishing the axes Animal hemisphere Vegetal hemisphere Animal pole Vegetal pole Point of sperm nucleus entry Gray crescent Pigmented cortex Future dorsal side First cleavage 10

11. FIGURE 47.22-2 Control egg (dorsal view) 2 1a1b Gray crescent Control group Experimental group Experimental egg (side view) Gray crescent Thread Normal Belly piece EXPERIMENT RESULTS 11

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) 12

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14. CELL FATE INDUCTION “Organizer” inactivate BM4 (bone morphogenic protein) on dorsal side Positional information and pattern formation relate to molecular signaling 14

15. 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

16. FIGURE 47.24 Limb buds 50  m Anterior Limb bud AER ZPA Posterior Apical ectodermal ridge (AER) (a) Organizer regions (b) Wing of chick embryo Digits Anterior Proximal Dorsal Posterior Ventral Distal 2 3 4 16

17. FIGURE 47.25 Donor limb bud Host limb bud ZPA Anterior Posterior New ZPA 4 4 3 3 2 2 EXPERIMENT RESULTS 17

18. 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

19. 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

20. MOST IMPORTANT TO REMEMBER PRODUCTS OF GENES ALLOW CELLS TO SPECIALIZE 20