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Chapter 47 Animal Development
From eggs to organisms
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)
Fertilization activate the egg and brings
together the nuclei of sperm and eggs
1. 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
2. The Cortical reaction
 release of Ca+2 from the site of sperm entry
 2nd messenger ( IP and DAG) induced by Ca+2
release opens Ca+2 channel on egg's’s ER
 cortical granule release content into periventilline
layer
 formation of fertilization envelope) slow block to
poly spermy
Figure 47.2 The acrosomal and cortical reactions during sea urchin
fertilization
Figure 47.3 A wave of Ca2+ release during the cortical reaction
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
Figure 47.4 Timeline for the fertilization of sea urchin eggs
Fertilization of mammals
1. 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
Figure 47.5 Fertilization in mammals
Cleavage partitions the zygote into many smaller cells
Three stages after fertilization
1. Cell division 細胞分裂期
 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
Figure 47.6 Cleavage in an echinoderm (sea urchin) embryo
45-90 min after
fertilization
Figure 47.7 The establishment of the body axes and the first cleavage
plane in an amphibian
(More concentrate yolk)
灰月區
Figure 47.8x Cleavage in a frog embryo
Animal pole
Vegetal
pole
2. Gastrulation 原腸期
 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…
Figure 47.9 Sea urchin gastrulation (Layer 1)
Figure 47.9 Sea urchin gastrulation (Layer 2)
Figure 47.9 Sea urchin gastrulation (Layer 3)
Figure 47.10 Gastrulation in a frog embryo
Table 47.1 Derivatives of the Three Embryonic Germ Layers in
Vertebrates
外胚層
內胚層
中胚層
3. Organogenesis器官形成
 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
Figure 47.11 Organogenesis in a frog embryo
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
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)
Figure 47.12 Cleavage, gastrulation, and early organogenesis in a
chick embryo
Figure 47.13 Organogenesis in a chick embryo
Figure 47.14 The development of extra embryonic membranes in a
chick
( filled with amnionic fluid for
protection)
(Waste storage)
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
The cellular and molecular basis of morphogenesis
and differentiation in Animals
Morphogenesis: cell movement , shape and position
change of developing cells
 invagination and evagination
Figure 47.16 Change in cellular shape during morphogenesis
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)
Figure 47.18 The extracellular matrix and cell migration
Figure 47.19 The role of a cadherin in frog blastula formation
CAM: cell adhesion molecule
cadhesrin
Experimental: inject with
antisense cadhedrin
control
The developmental fate of cells depends on the
cytoplasmic determinants and cell-cell induction
1. 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
Figure 47.20 Fate maps for two chordates
Figure 47.21 Experimental demonstration of the importance of cytoplasmic
determinants in amphibians
Figure 47.22 The “organizer” of Spemann and Mangold
Primary organizer of embryo
BMP-4( bone morphogenic proteins)
Locate at ventral side of gastrula
Organizer produce proteins to inhibit the BMP-4
activity
Figure 47.23 Organizer regions in vertebrate limb development
AER
AER( Apical Ectodermal Ridge)
 required for proximal-distal axis and patterning of
this axis
EGF: epidermal growth factor is responsible for the
growth signal
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
Figure 47.24 The experimental manipulation of positional information
Figure 47.6x Sea urchin development, from single cell to larva
Figure 47.8d Cross section of a frog blastula
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