Chapter 47 Animal Development

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Chapter 47 Animal Development
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From eggs to organisms
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Figure 47.1 A homunculus inside the head of a
human sperm
Preformation a series of successively smaller
embryos within embryos
Epigenesis the form of animal emerges gradually
from a formless eggs( Aristotle)
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Fertilization activate the egg and brings
together the nuclei of sperm and eggs
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• The Acrosomal reaction
• ?release of enzyme from acrosomal vesicle
• ? elongation of acrosomal process and
  penetration
• through jelly coat
• ? binding of acrosomal process to specific
• receptors on eggs
• ? fusion of sperm and egg plasma causes
  influx of
• sodium and membrane depolarization
• ? fast block to polyspermy

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2. The Cortical reaction ? release of Ca2
from the site of sperm entry ? 2nd messenger
( IP and DAG) induced by Ca2 release
opens Ca2 channel on egg'ss ER ? cortical
granule release content into periventilline
layer ? formation of fertilization
envelope) slow block to poly spermy
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Figure 47.2 The acrosomal and cortical reactions
during sea urchin fertilization
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Figure 47.3 A wave of Ca2 release during the
cortical reaction
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3. Activation of eggs ? DAG activate H
channel , causes pH change and induce
metabolic rate ? fusion of sperm and egg
nucleus ? DNA synthesis begin ? cell
division begins in 90 minutes
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Figure 47.4 Timeline for the fertilization of
sea urchin eggs
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• Fertilization of mammals
• Migration of sperm through follicle cells
• 2. Binding induces acrosomal reaction
• 3. Binding of sperm cells to ZP3 receptor in coat
  of
• zona pellucida
• 4. Nucleus of both eggs and sperm did not fuse
  until the 1st division of the zygote

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Figure 47.5 Fertilization in mammals
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• Cleavage partitions the zygote into many smaller
  cells
• Three stages after fertilization
• Cell division ?????
• ? cell undergo S and M phase of cell cycle
  but skip
• G1 and G2 phase
• ? partition cytoplasm of zygote into many
  smaller
• cells called blastomere ( distribution
  of different
• cytoplasmic content in the different
  regions)
• ? polarity defined by substances that are
• heterogeneously distributed in the
  cytoplasm of
• the eggs

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Figure 47.6 Cleavage in an echinoderm (sea
urchin) embryo
45-90 min after fertilization
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Figure 47.7 The establishment of the body axes
and the first cleavage plane in an amphibian
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Figure 47.8x Cleavage in a frog embryo
Animal pole
Vegetal pole
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2. Gastrulation ??? ? rearrangement of cells
of blastula ? transformation of blastula into
three layer embryonic germ layer ectoderm
nervous system and outer layer of skin
endoderm digestive tract and associated organs
mesoderm dermis, kidney, hearts, muscles
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Figure 47.9 Sea urchin gastrulation (Layer 1)
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Figure 47.9 Sea urchin gastrulation (Layer 2)
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Figure 47.9 Sea urchin gastrulation (Layer 3)
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Figure 47.10 Gastrulation in a frog embryo
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Table 47.1 Derivatives of the Three Embryonic
Germ Layers in Vertebrates
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3. Organogenesis???? ? folds, splits and dense
clustering( condensation) of cells ?
notochord ( dorsal mesoderm)?neuroplate(
dorsal ectoderm) ? somite ( mesoderm) ?
backbone of animals ?axial skeleton ?
morphogenesis and differentiation continue to
refine organs as they formed
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Figure 47.11 Organogenesis in a frog embryo
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Amniote embryos develop in a fluid filled sac
with shell or uterus Amniotes within the shells
or uterus, embryos
surrounded by fluid within a sac formed by
membrane called amnion
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• Avian development
• ? meroblastic cleavage cell division occurs
  only in
• a small yolk-free cytoplasm atop of the large
  mass
• of yolk
• ? The tissue layer out side the embryo develop
  into
• four extra embryonic membrane( yolk sac,
  amnion,
• chorion, and allantois)

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Figure 47.12 Cleavage, gastrulation, and early
organogenesis in a chick embryo
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Figure 47.13 Organogenesis in a chick embryo
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Figure 47.14 The development of extra embryonic
membranes in a chick
( filled with amnionic fluid for protection)
(Waste storage)
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Figure 47.15 Early development of a human embryo
and its extraembryonic membranes
7 days, 100 cells
implantation
Inward movement of epiblast starts the gatrulation
Development of extraembryonic membrane
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The cellular and molecular basis of morphogenesis
and differentiation in Animals Morphogenesis
cell movement , shape and position
change of developing cells
? invagination and
evagination
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Figure 47.16 Change in cellular shape during
morphogenesis
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Figure 47.17 Convergent extension of a sheet of
cells

• Convergent extension
• ? cells of tissue layer rearrange to become
  narrower
• and longer
• Possible guide by ECM( Ecm act as a track to
  guide
• the movement of the cells)

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Figure 47.18 The extracellular matrix and cell
migration
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Figure 47.19 The role of a cadherin in frog
blastula formation
CAM cell adhesion molecule cadhesrin
Experimental inject with antisense cadhedrin
control
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• The developmental fate of cells depends on the
  cytoplasmic determinants and cell-cell induction
• The heterogeneous distribution of cytoplasmic
• determinants in the unfertilized eggs lead
  to
• regional differentiation in the early
  embryo
• 2. Induction, interaction among the embryo
  cells
• themselves induces gene experssion

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Figure 47.20 Fate maps for two chordates
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Figure 47.21 Experimental demonstration of the
importance of cytoplasmic determinants in
amphibians
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Figure 47.22 The organizer of Spemann and
Mangold
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• BMP-4( bone morphogenic proteins)
• Locate at ventral side of gastrula
• Organizer produce proteins to inhibit the BMP-4
• activity

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Figure 47.23 Organizer regions in vertebrate
limb development
AER
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• AER( Apical Ectodermal Ridge)
• required for proximal-distal axis and
  patterning of
• this axis
• EGF epidermal growth factor is responsible for
  the
• growth signal

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• ZPA (Zone of Polarizing Area)
• Responsible for pattern formation along anterior-
• posterior axis
• ?secret sonic hedgehog, which is important for
  the
• growth of limb bud growth

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Figure 47.24 The experimental manipulation of
positional information
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Figure 47.6x Sea urchin development, from
single cell to larva
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Figure 47.8d Cross section of a frog blastula
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