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ANIMAL DEVELOPMENTCH. 47 MECHANISMS OF MORPHOGENESIS AND CELL FATE

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MECHANISMS OF MORPHOGENESISCell movement in Morphogenesis

Only animals experience cell movementCytoskeleton plays a large role

cells crawl within embryo using cytoskeletal fibers to extend and retract cellular protrusionsLike amoeboid movementCell adhesion molecules and ECM are involved

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FIGURE 47.15-5 Ectoderm

Neuralplate

Microtubules

Actinfilaments

Neural tube

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FIGURE 47.16

ExtensionConvergence

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MECHANISMS OF MORPHOGENESISApoptosis- programed cell death

example: tails cells in humansexample: inner digit cells

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CELL FATE SPECIFICATIONDetermination- cell or group of cells become committed to a particular fateDifferentiation is the resulting specializationAll cells have the same genes just a matter of gene expression

HHMI Embryonic Stem Cells and Cell Fatehttp://www.hhmi.org/biointeractive/creating-embryonic-stem-cell-lines

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CELL FATE SPECIFICATIONFate maps- diagrams showing the structures from each region of the embryo

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FIGURE 47.17Epidermis EpidermisCentral

nervoussystemNotochord

Mesoderm

EndodermBlastula 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

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CELL FATE SPECIFICATIONFate maps- diagrams showing the structures from each region of the embryoExample axis formation

bilateral symmetrygray crescent is the future dorsal side (opposite

sperm entry)different genes are expressed because different aprts are exposed to different environment

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FIGURE 47.21 DorsalRight

Anterior Posterior

VentralLeft

(a) The three axes of the fully developed embryo

(b) Establishing the axes

Animalhemisphere

Vegetalhemisphere

Animal pole

Vegetal pole

Point ofspermnucleusentry

Gray crescent

Pigmentedcortex

Futuredorsalside

First cleavage

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FIGURE 47.22-2

Control egg(dorsal view)

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1a 1b

Graycrescent

Controlgroup

Experimentalgroup

Experimental egg(side view)

Graycrescent

Thread

Normal NormalBelly piece

EXPERIMENT

RESULTS

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CAN CELL FATE BE MODIFIED?Development potential- what it can becomeFirst two cells are totipotent- can become a new organismMammals are totipotent to 8 cells 16 cells to trophoblast or (inner cell mass) cells are not totipotent but nuclei areThese cells would be pluripotent; can become almost any cell (can’t become the placenta)

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

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FORMATION OF VERTEBRATE LIMBSApical 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

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FIGURE 47.24

Limb buds50 m

AnteriorLimb bud

AER

ZPAPosterior

Apicalectodermalridge (AER)

(a) Organizer regions (b) Wing of chick embryo

Digits

Anterior

Proximal

DorsalPosterior

Ventral

Distal

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FIGURE 47.25

Donorlimbbud

Hostlimbbud

ZPA

Anterior

Posterior

New ZPA

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4

3

3

2 2

EXPERIMENT

RESULTS

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FORMATION OF VERTEBRATE LIMBSSonic 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.

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CILIA AND CELL FATE

MonociliaStationary single projections on nearly all animal cellsA19cts as antenna on cell surface to receive signals from multiple proteins

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MOST IMPORTANT TO REMEMBER

PRODUCTS OF GENES ALLOW CELLS TO SPECIALIZE