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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.
Figure 47.2
EMBRYONIC DEVELOPMENT
Sperm
Zygote
Adult
frog
Egg
Metamorphosis
Blastula
Larval
stages
Gastrula
Tail-bud
embryo
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.
Fertilization
• Molecules and events at the egg surface play a
crucial role in each step of fertilization
– Sperm penetrate the protective layer around the
egg
– Receptors on the egg surface bind to molecules
on the sperm surface
– Changes at the egg surface prevent polyspermy,
the entry of multiple sperm nuclei into the egg
© 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 47.3-5
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.
Egg Activation
• The rise in Ca2+ in the cytosol increases the rates
of cellular respiration and protein synthesis by the
egg cell
• With these rapid changes in metabolism, the egg
is said to be activated
• The proteins and mRNAs needed for activation
are already present in the egg
• The sperm nucleus merges with the egg nucleus
and cell division begins
© 2011 Pearson Education, Inc.
• In mammals the first cell division occurs 1236
hours after sperm binding
• The diploid nucleus forms after this first division of
the zygote
© 2011 Pearson Education, Inc.
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
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.
Gastrulation
• Gastrulation rearranges the cells of a blastula
into a three-layered embryo, called a gastrula
© 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
© 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)
• Cells continue to move from the embryo surface
into the embryo by involution
• These cells become the endoderm and
mesoderm
• Cells on the embryo surface will form the
ectoderm
© 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
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.
• In both adaptations, embryos are surrounded
by fluid in a sac called the amnion
• This protects the embryo from desiccation and
allows reproduction on dry land
• Mammals and reptiles including birds are
called amniotes for this reason
© 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)
© 2011 Pearson Education, Inc.
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.
• Cells in a multicellular organism share the same
genome
• Differences in cell types are the result of the
expression of different sets of genes
© 2011 Pearson Education, Inc.
Fate Mapping
• Fate maps are diagrams showing organs and
other structures that arise from each region of an
embryo
• Classic studies using frogs indicated that cell
lineage in germ layers is traceable to blastula cells
© 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
• Later studies of C. elegans used the ablation
(destruction) of single cells to determine the
structures that normally arise from each cell
• The researchers were able to determine the
lineage of each of the 959 somatic cells in the
worm
© 2011 Pearson Education, Inc.
Time after fertilization (hours)
Figure 47.18
Zygote
0
First cell division
Nervous
system,
outer skin,
musculature
10
Musculature, gonads
Outer skin,
nervous system
Germ line
(future
gametes)
Musculature
Hatching
Intestine
Intestine
Anus
Mouth
Eggs
Vulva
POSTERIOR
ANTERIOR
1.2 mm
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
• In mammals, embryonic cells remain totipotent
until the 8-cell stage, much longer than other
organisms
• Progressive restriction of developmental potential
is a general feature of development in all animals
• In general tissue-specific fates of cells are fixed by
the late gastrula stage
© 2011 Pearson Education, Inc.