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LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 47
Animal Development
Lectures by
Erin Barley
Kathleen Fitzpatrick
© 2011 Pearson Education, Inc.
Overview: A Body-Building Plan
• A human embryo at about 7 weeks after
conception shows development of distinctive
features
1 mm
© 2011 Pearson Education, Inc.
Concept 47.1: Fertilization and cleavage
initiate embryonic development
• Fertilization is the formation of a diploid zygote
from a haploid egg and sperm
© 2011 Pearson Education, Inc.
The Acrosomal Reaction
• The acrosomal reaction is triggered when the
sperm meets the egg
• The acrosome at the tip of the sperm releases
hydrolytic enzymes that digest material
surrounding the egg
© 2011 Pearson Education, Inc.
Figure 47.3-1
Basal body
(centriole)
Sperm
head
Acrosome
Jelly coat
Sperm-binding
receptors
Vitelline layer
Egg plasma membrane
Figure 47.3-2
Basal body
(centriole)
Sperm
head
Acrosome
Jelly coat
Sperm-binding
receptors
Hydrolytic enzymes
Vitelline layer
Egg plasma membrane
Figure 47.3-3
Sperm
nucleus
Basal body
(centriole)
Sperm
head
Acrosome
Jelly coat
Sperm-binding
receptors
Acrosomal
process
Actin
filament
Hydrolytic enzymes
Vitelline layer
Egg plasma membrane
Figure 47.3-4
Sperm
plasma
membrane
Sperm
nucleus
Basal body
(centriole)
Sperm
head
Acrosome
Jelly coat
Sperm-binding
receptors
Acrosomal
process
Actin
filament
Fused
plasma
membranes
Hydrolytic enzymes
Vitelline layer
Egg plasma membrane
Figure 47.3-5
Sperm
plasma
membrane
Sperm
nucleus
Basal body
(centriole)
Sperm
head
Acrosome
Jelly coat
Sperm-binding
receptors
Fertilization
envelope
Acrosomal
process
Actin
filament
Cortical
Fused
granule
plasma
membranes
Hydrolytic enzymes
Perivitelline
space
Vitelline layer
Egg plasma membrane
EGG CYTOPLASM
• Gamete contact and/or fusion depolarizes the egg
cell membrane and sets up a fast block to
polyspermy
© 2011 Pearson Education, Inc.
The Cortical Reaction
• Fusion of egg and sperm also initiates the cortical
reaction
• Seconds after the sperm binds to the egg, vesicles
just beneath the egg plasma membrane release
their contents and form a fertilization envelope
• The fertilization envelope acts as the slow block
to polyspermy
© 2011 Pearson Education, Inc.
• The cortical reaction requires a high concentration
of Ca2 ions in the egg
• The reaction is triggered by a change in Ca2
concentration
• Ca2 spread across the egg correlates with the
appearance of the fertilization envelope
© 2011 Pearson Education, Inc.
Fertilization in Mammals
• Fertilization in mammals and other terrestrial
animals is internal
• Secretions in the mammalian female reproductive
tract alter sperm motility and structure
• This is called capacitation and must occur before
sperm are able to fertilize an egg
© 2011 Pearson Education, Inc.
• Sperm travel through an outer layer of cells to
reach the zona pellucida, the extracellular matrix
of the egg
• When the sperm binds a receptor in the zona
pellucida, it triggers a slow block to polyspermy
• No fast block to polyspermy has been identified in
mammals
© 2011 Pearson Education, Inc.
Figure 47.5
Zona pellucida
Follicle cell
Sperm
basal body
Sperm
nucleus
Cortical
granules
Cleavage
• Fertilization is followed by cleavage, a period of
rapid cell division without growth
• Cleavage partitions the cytoplasm of one large cell
into many smaller cells called blastomeres
• The blastula is a ball of cells with a fluid-filled
cavity called a blastocoel
© 2011 Pearson Education, Inc.
Figure 47.6
50 m
(a) Fertilized egg
(b) Four-cell stage (c) Early blastula
(d) Later blastula
Cleavage Patterns
• In frogs and many other animals, the distribution of
yolk (stored nutrients) is a key factor influencing
the pattern of cleavage
• The vegetal pole has more yolk; the animal pole
has less yolk
• The difference in yolk distribution results in animal
and vegetal hemispheres that differ in appearance
© 2011 Pearson Education, Inc.
Figure 47.7
Zygote
2-cell
stage
forming
Gray crescent
0.25 mm
8-cell stage (viewed
from the animal pole)
4-cell
stage
forming
8-cell
stage
Animal
pole
0.25 mm
Blastula (at least 128 cells)
Vegetal pole
Blastula
(cross
section)
Blastocoel
Figure 47.7a-5
Animal pole
Gray crescent
Zygote
2-cell stage
forming
Blastocoel
Vegetal pole
4-cell stage
forming
8-cell stage
Blastula
(cross section)
Concept 47.2: Morphogenesis in animals
involves specific changes in cell shape,
position, and survival
• After cleavage, the rate of cell division slows and
the normal cell cycle is restored
• Morphogenesis, the process by which cells
occupy their appropriate locations, involves
– Gastrulation, the movement of cells from the
blastula surface to the interior of the embryo
– Organogenesis, the formation of organs
© 2011 Pearson Education, Inc.
• The three layers produced by gastrulation are
called embryonic germ layers
– The ectoderm forms the outer layer
– The endoderm lines the digestive tract
– The mesoderm partly fills the space between the
endoderm and ectoderm
• Each germ layer contributes to specific structures
in the adult animal
Video: Sea Urchin Embryonic Development
© 2011 Pearson Education, Inc.
Figure 47.8
ECTODERM (outer layer of embryo)
• Epidermis of skin and its derivatives (including sweat glands,
hair follicles)
• Nervous and sensory systems
• Pituitary gland, adrenal medulla
• Jaws and teeth
• Germ cells
MESODERM (middle layer of embryo)
• Skeletal and muscular systems
• Circulatory and lymphatic systems
• Excretory and reproductive systems (except germ cells)
• Dermis of skin
• Adrenal cortex
ENDODERM (inner layer of embryo)
• Epithelial lining of digestive tract and associated organs
(liver, pancreas)
• Epithelial lining of respiratory, excretory, and reproductive tracts
and ducts
• Thymus, thyroid, and parathyroid glands
Gastrulation in Sea Urchins
• Gastrulation begins at the vegetal pole of the
blastula
• Mesenchyme cells migrate into the blastocoel
• The vegetal plate forms from the remaining cells of
the vegetal pole and buckles inward through
invagination
© 2011 Pearson Education, Inc.
• The newly formed cavity is called the
archenteron
• This opens through the blastopore, which will
become the anus
© 2011 Pearson Education, Inc.
Figure 47.9
Animal
pole
Blastocoel
Mesenchyme
cells
Vegetal plate
Vegetal
pole
Blastocoel
Filopodia
Mesenchyme
cells
Blastopore
Archenteron
50 m
Blastocoel
Ectoderm
Key
Future ectoderm
Future mesoderm
Future endoderm
Mouth
Mesenchyme
(mesoderm forms
future skeleton)
Archenteron
Blastopore
Digestive tube (endoderm)
Anus (from blastopore)
Gastrulation in Frogs
• Frog gastrulation begins when a group of cells on
the dorsal side of the blastula begins to
invaginate
• This forms a crease along the region where the
gray crescent formed
• The part above the crease is called the dorsal lip
of the blastopore
© 2011 Pearson Education, Inc.
Figure 47.10
1
CROSS SECTION
SURFACE VIEW
Animal pole
Blastocoel
Dorsal
lip of
blastopore
Early
Vegetal pole
gastrula
Blastopore
Blastocoel
shrinking
2
3
Blastocoel
remnant
Dorsal
lip of
blastopore
Archenteron
Ectoderm
Mesoderm
Endoderm
Key
Future ectoderm
Future mesoderm
Future endoderm
Late
gastrula
Blastopore
Blastopore
Yolk plug
Archenteron
Figure 47.11
Fertilized egg
Primitive
streak
Embryo
Yolk
Primitive streak
Epiblast
Future
ectoderm
Blastocoel
Migrating
cells
(mesoderm)
Endoderm
Hypoblast
YOLK
Gastrulation in Humans
• Human eggs have very little yolk
• A blastocyst is the human equivalent of the
blastula
• The inner cell mass is a cluster of cells at one
end of the blastocyst
• The trophoblast is the outer epithelial layer of the
blastocyst and does not contribute to the embryo,
but instead initiates implantation
© 2011 Pearson Education, Inc.
Figure 47.12
1 Blastocyst reaches uterus.
Uterus
Endometrial epithelium
(uterine lining)
Inner cell mass
Trophoblast
Blastocoel
2 Blastocyst implants
(7 days after fertilization).
Expanding region of
trophoblast
Maternal
blood
vessel
Epiblast
Hypoblast
Trophoblast
3 Extraembryonic membranes
start to form (10–11 days),
and gastrulation begins
(13 days).
Expanding region of
trophoblast
Amniotic cavity
Epiblast
Hypoblast
Yolk sac (from hypoblast)
Extraembryonic mesoderm cells
(from epiblast)
Chorion (from trophoblast)
4 Gastrulation has produced a
three-layered embryo with
four extraembryonic
membranes.
Amnion
Chorion
Ectoderm
Mesoderm
Endoderm
Yolk sac
Extraembryonic mesoderm
Allantois
Figure 47.12a
Endometrial epithelium
(uterine lining)
Uterus
Inner cell mass
Trophoblast
Blastocoel
1 Blastocyst reaches uterus.
Figure 47.12b
Expanding region of
trophoblast
Maternal
blood
vessel
Epiblast
Hypoblast
Trophoblast
2 Blastocyst implants
(7 days after fertilization).
Figure 47.12c
Expanding region of
trophoblast
Amniotic cavity
Epiblast
Hypoblast
Yolk sac (from hypoblast)
Extraembryonic mesoderm
cells (from epiblast)
Chorion (from trophoblast)
3 Extraembryonic membranes
start to form (10–11 days),
and gastrulation begins
(13 days).
Figure 47.12d
Amnion
Chorion
Ectoderm
Mesoderm
Endoderm
Yolk sac
Extraembryonic mesoderm
Allantois
4 Gastrulation has produced a
three-layered embryo with
four extraembryonic
membranes.
Developmental Adaptations of Amniotes
• The colonization of land by vertebrates was made
possible only after the evolution of
– The shelled egg of birds and other reptiles as well
as monotremes (egg-laying mammals)
– The uterus of marsupial and eutherian mammals
© 2011 Pearson Education, Inc.
• The four extraembryonic membranes that form
around the embryo
–
–
–
–
The chorion functions in gas exchange
The amnion encloses the amniotic fluid
The yolk sac encloses the yolk
The allantois disposes of waste products and
contributes to gas exchange
© 2011 Pearson Education, Inc.
Organogenesis
• During organogenesis, various regions of the
germ layers develop into rudimentary organs
• Early in vertebrate organogenesis, the notochord
forms from mesoderm, and the neural plate forms
from ectoderm
© 2011 Pearson Education, Inc.
Figure 47.13
Eye
Neural folds
Neural
fold
Tail bud
Neural plate
SEM
1 mm
Neural
fold
Somites
Neural tube
Neural
plate
Notochord
Neural
crest cells
1 mm
Neural
crest
cells
Coelom
Notochord
Somite
Ectoderm
Mesoderm
Endoderm
Neural
crest cells
Outer layer
of ectoderm
Archenteron
(a) Neural plate formation
Neural
tube
(b) Neural tube formation
Archenteron
(digestive
cavity)
(c) Somites
• The neural plate soon curves inward, forming the
neural tube
• The neural tube will become the central nervous
system (brain and spinal cord)
Video: Frog Embryo Development
© 2011 Pearson Education, Inc.
Figure 47.13b-3
Neural
fold
Neural plate
Neural
crest cells
Neural
crest cells
(b) Neural tube formation
Neural
tube
Outer layer
of ectoderm
Figure 47.13c
Eye
SEM
Neural tube
Notochord
Coelom
Somites
Tail bud
1 mm
Neural
crest
cells
Somite
(c) Somites
Archenteron
(digestive
cavity)
Figure 47.14
Neural tube
Notochord
Eye
Forebrain
Somite
Coelom
Endoderm
Mesoderm
Ectoderm
Archenteron
Lateral
fold
Heart
Blood
vessels
Somites
Yolk stalk
These layers
form extraembryonic
membranes.
(a) Early organogenesis
Yolk sac
Neural
tube
YOLK
(b) Late organogenesis
Mechanisms of Morphogenesis
• Morphogenesis in animals but not plants involves
movement of cells
© 2011 Pearson Education, Inc.
Figure 47.15-1
Ectoderm
Figure 47.15-2
Ectoderm
Neural
plate
Microtubules
Figure 47.15-3
Ectoderm
Neural
plate
Microtubules
Actin
filaments
Figure 47.15-4
Ectoderm
Neural
plate
Microtubules
Actin
filaments
Figure 47.15-5
Ectoderm
Neural
plate
Microtubules
Actin
filaments
Neural tube
• The cytoskeleton promotes elongation of the
archenteron in the sea urchin embryo
• This is convergent extension, the
rearrangement of cells of a tissue that cause it to
become narrower (converge) and longer (extend)
• Convergent extension occurs in other
developmental processes
• The cytoskeleton also directs cell migration
© 2011 Pearson Education, Inc.
Figure 47.16
Programmed Cell Death
• Programmed cell death is also called apoptosis
• At various times during development, individual
cells, sets of cells, or whole tissues stop
developing and are engulfed by neighboring cells
• For example, many more neurons are produced in
developing embryos than will be needed
• Extra neurons are removed by apoptosis
© 2011 Pearson Education, Inc.
Concept 47.3: Cytoplasmic determinants
and inductive signals contribute to cell
fate specification
• Determination is the term used to describe the
process by which a cell or group of cells becomes
committed to a particular fate
• Differentiation refers to the resulting
specialization in structure and function
© 2011 Pearson Education, Inc.
Figure 47.17
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
Figure 47.21
Dorsal
Right
Anterior
Posterior
Left
Ventral
(a) The three axes of the fully developed embryo
Animal pole
Animal
hemisphere
Vegetal
hemisphere
Vegetal pole
(b) Establishing the axes
Point of
sperm
nucleus
entry
Gray
crescent
Pigmented
cortex
Future
dorsal
side
First
cleavage
Restricting Developmental Potential
• Hans Spemann performed experiments to
determine a cell’s developmental potential (range
of structures to which it can give rise)
• Embryonic fates are affected by distribution of
determinants and the pattern of cleavage
• The first two blastomeres of the frog embryo are
totipotent (can develop into all the possible cell
types)
© 2011 Pearson Education, Inc.
Figure 47.22-1
EXPERIMENT
Control egg
(dorsal view)
Experimental egg
(side view)
1a Control
group
Gray
crescent
1b Experimental
group
Gray
crescent
Thread
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
RESULTS
Normal
Belly piece
Normal
Formation of the Vertebrate Limb
• Inductive signals play a major role in pattern
formation, development of spatial organization
• The molecular cues that control pattern formation
are called positional information
• This information tells a cell where it is with respect
to the body axes
• It determines how the cell and its descendents
respond to future molecular signals
© 2011 Pearson Education, Inc.
• The wings and legs of chicks, like all vertebrate
limbs, begin as bumps of tissue called limb buds
© 2011 Pearson Education, Inc.
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
(a) Organizer regions
(b) Wing of chick embryo
Figure 47.24b
2
Digits
Anterior
3
4
Ventral
Distal
Proximal
Dorsal
Posterior
(b) Wing of chick embryo
Figure 47.25
EXPERIMENT
Anterior
New
ZPA
Donor
limb
bud
Host
limb
bud
ZPA
Posterior
RESULTS
4
3
2
2
4
3
• Sonic hedgehog is an inductive signal for limb
development
• Hox genes also play roles during limb pattern
formation
© 2011 Pearson Education, Inc.
Cilia and Cell Fate
• Ciliary function is essential for proper specification
of cell fate in the human embryo
• Motile cilia play roles in left-right specification
• Monocilia (nonmotile cilia) play roles in normal
kidney development
© 2011 Pearson Education, Inc.
Figure 47.26
Lungs
Heart
Liver
Spleen
Stomach
Large intestine
Normal location
of internal organs
Location in
situs inversus