ANIMAL
DEVELOPMENT
1
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
2
cells crawl within embryo using cytoskeletal
fibers to extend and retract cellular protrusions
Like amoeboid movement
Cell adhesion molecules and ECM are involved
Ectoderm
Neural
plate
Microtubules
Actin
filaments
Neural tube
3
FIGURE 47.15-5
4
FIGURE 47.16
MECHANISMS OF
MORPHOGENESIS
Apoptosis- programed cell death
example: tails cells in humans
5
example: inner digit cells
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
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http://www.hhmi.org/biointeractive/creating-embryonic-stemcell-lines
CELL FATE
SPECIFICATION
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Fate maps- diagrams showing the structures from each
region of the embryo
Epidermis
Central
nervous
system
Notochord
Epidermis
Mesoderm
Endoderm
Blastula
Neural 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
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FIGURE 47.17
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)
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different genes are expressed because different aprts
are exposed to different environment
FIGURE 47.21
Dorsal
Right
Anterior
Posterior
Left
Ventral
(a) The three axes of the fully developed embryo
Animal pole
Vegetal
hemisphere
Vegetal pole
(b) Establishing the axes
Point of
sperm
nucleus
entry
Pigmented
cortex
Future
dorsal
side
Gray
crescent
10
Animal
hemisphere
First
cleavage
FIGURE 47.22-2
EXPERIMENT
Control egg
(dorsal view)
Experimental egg
(side view)
1a Control
1b Experimental
group
group
Gray
crescent
Gray
crescent
Thread
2
Normal
Belly piece
Normal
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RESULTS
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
12
These 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 side
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Positional information and pattern formation relate to
molecular signaling
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.
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Hox genes determine if front or hind limbs
FIGURE 47.24
Anterior
Limb bud
AER
ZPA
Posterior
Limb buds
50 m
2
Digits
Apical
ectodermal
ridge (AER)
Anterior
3
4
Ventral
Proximal
Distal
Dorsal
Posterior
(b) Wing of chick embryo
16
(a) Organizer regions
EXPERIMENT
Anterior
New
ZPA
Donor
limb
bud
Host
limb
bud
ZPA
Posterior
RESULTS
4
3
2
2
4
3
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FIGURE 47.25
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.
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SSH remains important in the adult. It controls cell
division of adult stem cells and has been
implicated in development of some cancers.
CILIA AND CELL FATE
Monocilia
Stationary single
projections on nearly
all animal cells
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A19cts as antenna
on cell surface to
receive signals from
multiple proteins
MOST IMPORTANT TO
REMEMBER
20
PRODUCTS OF
GENES ALLOW
CELLS TO
SPECIALIZE