Download ANIMAL DEVELOPMENT

ANIMAL
DEVELOPMENT
E l ti off
Evolution
Development
(Evo/Devo)
(
)
evolutionaryy
developmental
bi l
biology
Figure 47.6
50 m
(a) Fertilized egg
(b) Four-cell stage (c) Early blastula
( ) Later blastula
(d)
Figure 27.UN01
Eukarya
Archaea
Bacteria
Figure 32.11
Ct
Ctenophora
h
Eumeta
azoa
Me
etazoa
ANCESTRAL
COLONIAL
FLAGELLATE
Porifera
Cnidaria
Acoela
Bilateria
Chordata
Platyhelminthes
L
Lophotro
ochozoa
a Ecdysozoa
Deute
erostomiia
Echinodermata
Rotifera
Ectoprocta
Brachiopoda
Mollusca
Annelida
Nematoda
Arthropoda
ontogeny recapitulates phylogeny
phylogeny"" (ORP
ORP))
我們的身體裡有一條魚
我們的身體裡有
條魚
Recapitulation theory


The theory of recapitulation,
recapitulation, often
expressed as "ontogeny recapitulates
phylogeny"" (ORP
phylogeny
ORP))- is a hypothesis that in
developing from embryo to adult, animals go
through
g stages
g resembling
g or representing
p
g
successive stages in the evolution of their
remote ancestors..
Th conceptt originated
The
i i t d iin th
the 1790
1790s among
the German Natural philosophers and, as
proposed
p
p
by
y Étienne Serres in 1824–
1824–26,,
became known as the "Meckel"Meckel-Serres Law".
In 1866, the German zoologist Ernst
Haeckel proposed that the embryonic
development of an individual organism (its
ontogeny) followed the same path as the
evolutionary history of its species (its
phylogeny).
Ontogeny recapitulates
Phylogeny"" (ORP
Phylogeny
ORP))
Ontogeny recapitulates
Ph l
Phylogeny
can nott explain
l i
chick development
p
This is clearly not the case — a fact
recognized by many scientists even when
the idea of ontogeny recapitulating
phylogeny was introduced. If you observe a
chick's
chick
s development,
development you will find that the
chick embryo may resemble the embryos of
reptiles and fish at points in its development,
but it doesn't recapitulate the forms of its
adult ancestors.
Root of EvoEvo-Devo
Edward B. Lewis discovered homeotic
genes rooting the emerging discipline of
genes,
evo--devo in molecular genetics.
evo
genetics. In 2000,
a special section of the Proceedings of
the National Academy of Sciences
(PNAS) was devoted to "evo"evo
evo-devo
devo",and
and
an entire 2005 issue of the Journal of
Experimental Zoology Part B: Molecular
and Developmental Evolution was
devoted to the key evoevo-devo topics of
evolutionary innovation and
morphological novelty
novelty.
Edward B. Lewis a Nobel Prize
winner in 1995
His Nobel Prize winning studies with
Drosophila,, (including the discovery of the
Drosophila
Drosophila Bithorax complex and elucidation of
its function)
function), founded the field of
developmental genetics and laid the
groundwork for our current understanding of
th universal,
the
i
l evolutionarily
l ti
il conserved
d
strategies controlling animal development. He
is credited with development of the
complementation
l
t ti test.
test
t t. His
Hi kkey publications
bli ti
iin
the fields of genetics
genetics,, developmental biology,
biology,
radiation and cancer are presented in the book
G
Genes,
Development and Cancer,
Cancer
C
, which was
released in 2004.
Model
Og i
Organisms
生物 experimental
i
t l models
d l
Escherchia coli
大腸菌
Saccharomyces
cerevisiae
Dictyostelium
discoideum
酵母菌
黏菌
Dictyostelium
y
discoideum
黏菌
Caenorhabditis elegans
秀麗線蟲
Drosophila
melanogaster
Xenopus laevis
蛙
果蠅
Danio rerio
斑馬魚
Arabidopsis
p
thaliana
阿拉伯芥
The mouse as a model for human development
人
小鼠
Ontogeny recapitulates Phylogeny
Phylogeny""
(ORP
ORP))
This idea is an extreme one. If it were strictly true, it
would predict, for example, that in the course of a
chick's development, it would go through the following
stages:
g
a single
g celled organism,
g
a multi-celled
invertebrate ancestor, a fish, a lizard-like reptile, an
ancestral bird,, and then finally,
y, a babyy chick.
Ancestral characters are often, but not always,
preserved in an organism
organism'ss development. For
example, both chick and human embryos go
through a stage where they have slits and
arches in their necks like the gill slits and gill
arches of fish. These structures are not gills and
do not develop into gills in chicks and humans
humans,
but the fact that they are so similar to gill
structures in fish at this p
point in development
p
supports the idea that chicks and humans share
a common ancestor with fish. Thus,
developmental characters, along with other lines
of evidence, can be used for constructing
phylogenies
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
p
Lectures by
Erin Barley
Kathleen Fitzpatrick
© 2011 Pearson Education, Inc.
Figure 32.11
Ct
Ctenophora
h
Eumeta
azoa
Me
etazoa
ANCESTRAL
COLONIAL
FLAGELLATE
Porifera
Cnidaria
Acoela
Bilateria
Chordata
Platyhelminthes
L
Lophotro
ochozoa
a Ecdysozoa
Deute
erostomiia
Echinodermata
Rotifera
Ectoprocta
Brachiopoda
Mollusca
Annelida
Nematoda
Arthropoda
Figure 32.10
Porifera
Cnidaria
Eum
metazoa
M
Metazoa
ANCESTRAL
COLONIAL
FLAGELLATE
Ctenophora
Pro
otostomiia
Billateria
Deutero
ostomia
a
Ectoprocta
Brachiopoda
p
Echinodermata
Chordata
Platyhelminthes
R tif
Rotifera
Mollusca
Annelida
Arthropoda
Nematoda
Figure 32.UN02
535–525 mya:
Cambrian explosion
565 mya:
Ediacaran biota
365 mya:
Early land
animals
Origin and
diversification
of dinosaurs
Diversification
of mammals
Era
Paleozoic
Neoproterozoic
1,000
542
251
Millions of years ago (mya)
Mesozoic
Cenozoic
65.5
0
Concept : Animal are multicellular,
heterotrophic eukaryotes with tissues that
d l from
develop
f
embryonic
b
i layers
l
• Th
There are exceptions
ti
to
t nearly
l every criterion
it i ffor
distinguishing animals from other life-forms
• Several
S
l characteristics,
h
t i ti
ttaken
k ttogether,
th sufficiently
ffi i tl
define the group
• Animals
A i l are h
heterotrophs
t t h th
thatt iingestt th
their
i ffood
d
© 2011 Pearson Education, Inc.
Cell Structure and Specialization
• Animals are multicellular eukaryotes
• Their cells lack cell walls
g
by
y structural
• Their bodies are held together
proteins such as collagen
• Nervous tissue and muscle tissue are unique,
defining characteristics of animals
• Tissues are groups of cells that have a common
structure, function, or both
© 2011 Pearson Education, Inc.
Reproduction and Development
• Most animals reproduce sexually
sexually, with the diploid
stage usually dominating the life cycle
• After a sperm fertilizes an egg
egg, the zygote
undergoes rapid cell division called cleavage
• Cleavage
Cl
leads
l d to
t formation
f
ti off a multicellular,
lti ll l
hollow blastula
• The blastula undergoes gastrulation, forming a
gastrula with different layers of embryonic tissues
© 2011 Pearson Education, Inc.
Figure 32.2-1
Zygote
Z
t
Cleavage
Eight-cell
stage
g
Figure 32.2-2
Zygote
Z
t
Cleavage
Blastocoel
Cleavage
Eight-cell
stage
g
Blastula
Cross section
of blastula
Figure 32.2-3
Zygote
Z
t
Cleavage
Blastocoel
Cleavage
Eight-cell
stage
g
Blastula
Cross section
of blastula
Gastrulation
Blastocoel
Endoderm
Ectoderm
Archenteron
Cross section
of gastrula
Bl t
Blastopore
RESULTS
1 Early stages of
d
development
l
100 m
Figure 32.6
2 32-cell stage
Site of
gastrulation
3 Early gastrula
stage
g
4 Embryos with
blocked -catenin
activity
Site of
gastrulation
• Many animals have at least one larval stage
• A larva is sexually immature and morphologically
distinct from the adult; it eventually undergoes
metamorphosis
• A juvenile
j
il resembles
bl an adult,
d lt but
b t iis nott yett
sexually mature
© 2011 Pearson Education, Inc.
• Most animals,
animals and only animals
animals, have Hox genes
that regulate the development of body form
• Although the Hox family of genes has been highly
conserved, it can produce a wide diversity of
animal morphology
© 2011 Pearson Education, Inc.
Concept : The history of animals spans
more than half a billion years
• The animal kingdom includes a great diversity of
living species and an even greater diversity of
extinct ones
• The
Th common ancestor
t off living
li i animals
i l may h
have
lived between 675 and 800 million years ago
• This ancestor may have resembled modern
choanoflagellates, protists that are the closest
living relatives of animals
© 2011 Pearson Education, Inc.
Figure 32.3
Individual
choanoflagellate
Ch
Choanoflagellates
fl
ll t
OTHER
EUKARYOTES
Sponges
An
nimals
Other animals
Collar cell
(choanocyte)
Neoproterozoic Era (1 Billion
Billion–542
542 Million
Years Ago)
• Early members of the animal fossil record include
the Ediacaran biota
biota, which dates from 565 to 550
million years ago
© 2011 Pearson Education, Inc.
Mesozoic Era (251
(251–65
65.55 Million Years Ago)
• Coral reefs emerged
emerged, becoming important marine
ecological niches for other organisms
• The ancestors of plesiosaurs were reptiles that
returned to the water
• During
D i th
the M
Mesozoic
i era, di
dinosaurs were th
the
dominant terrestrial vertebrates
• The first mammals emerged
gp
plants and insects diversified
• Flowering
© 2011 Pearson Education, Inc.
Cenozoic Era (65.5 Million Years Ago to
the Present)
• The beginning of the Cenozoic era followed mass
extinctions of both terrestrial and marine animals
• These extinctions included the large, nonflying
di
dinosaurs
and
d th
the marine
i reptiles
til
• Mammals increased in size and exploited vacated
ecological niches
global climate cooled
• The g
© 2011 Pearson Education, Inc.
Concept : Animals can be characterized by
“body plans”
• Zoologists sometimes categorize animals
according to a body plan,
plan a set of morphological
and developmental traits
• Some
S
developmental
d
l
t l characteristics
h
t i ti are
conservative
 For example, the molecular control of gastrulation
is conserved among diverse animal groups
© 2011 Pearson Education, Inc.
Symmetry
• Animals can be categorized according to the
symmetry of their bodies, or lack of it
• Some animals have radial symmetry
symmetry, with no
front and back, or left and right
© 2011 Pearson Education, Inc.
Figure 32.7
(a) Radial symmetry
(b) Bilateral symmetry
• Two
Two-sided
sided symmetry is called bilateral symmetry
• Bilaterally symmetrical animals have
–
–
–
–
A dorsal (top) side and a ventral (bottom) side
A right and left side
Anterior (head) and posterior (tail) ends
Cephalization, the development of a head
© 2011 Pearson Education, Inc.
• Radial animals are often sessile or planktonic
(drifting or weakly swimming)
• Bilateral animals often move actively and have a
central nervous system
© 2011 Pearson Education, Inc.
Tissues
• Animal body plans also vary according to the
organization of the animal’s tissues
• Tissues are collections of specialized cells isolated
from other tissues by membranous layers
• During
D i d
development,
l
t th
three germ llayers give
i rise
i tto
the tissues and organs of the animal embryo
© 2011 Pearson Education, Inc.
• Ectoderm is the germ layer covering the embryo’s
embryo s
surface
• Endoderm is the innermost germ layer and lines
the developing digestive tube, called the
archenteron
© 2011 Pearson Education, Inc.
Figure 32.8
(a) Coelomate
Coelom
Digestive tract
(from endoderm)
Body covering
(f
(from
ectoderm)
t d
)
Tissue layer
lining coelom
and
d suspending
di
internal organs
(from mesoderm)
(b) Pseudocoelomate
Body covering
(from ectoderm)
Pse docoelom
Pseudocoelom
Digestive tract
(from endoderm)
Muscle layer
(from
mesoderm)
(c) Acoelomate
Body covering
Tissue(f
(from
ectoderm)
d
) Ti
filled region
(from
mesoderm)
Wall of digestive cavity
(from endoderm)
• Coelomates and pseudocoelomates belong to the
same grade
• A grade is a group whose members share key
biological features
• A grade
d iis nott necessarily
il a clade,
l d an ancestor
t
and all of its descendents
© 2011 Pearson Education, Inc.
Protostome and Deuterostome Development
• Based on early development
development, many animals can
be categorized as having protostome
development or deuterostome development
© 2011 Pearson Education, Inc.
Cleavage
• In protostome development
development, cleavage is spiral
and determinate
• In deuterostome development
development, cleavage is radial
and indeterminate
• With iindeterminate
d t
i t cleavage,
l
each
h cellll iin th
the early
l
stages of cleavage retains the capacity to develop
i t a complete
into
l t embryo
b
• Indeterminate cleavage makes possible identical
twins, and embryonic stem cells
© 2011 Pearson Education, Inc.
Figure 32.9
Protostome development
(examples: molluscs,
annelids)
( ) Cleavage
(a)
Cl
Deuterostome development
(examples: echinoderms,
chordates)
Eight-cell stage
Eight-cell stage
Spiral and determinate
Radial and indeterminate
(b) Coelom formation
Coelom
Archenteron
Coelom
Mesoderm
Blastopore
Blastopore
Solid masses of mesoderm
split and form coelom.
(c) Fate of the
blastopore
Mesoderm
Folds of archenteron
form coelom.
Anus
Mouth
Digestive tube
Key
Ectoderm
Mesoderm
Endoderm
Mouth
Mouth develops from blastopore.
Anus
Anus develops from blastopore.
Figure 32.9a
(a) Cleavage
Protostome development
(examples: molluscs,
annelids))
Eight-cell stage
Deuterostome development
(examples: echinoderms,
chordates))
Eight-cell stage
Key
Ectoderm
Mesoderm
Endoderm
Spiral and determinate
Radial and indeterminate
Coelom Formation
• In protostome development
development, the splitting of solid
masses of mesoderm forms the coelom
• In deuterostome development
development, the mesoderm
buds from the wall of the archenteron to form the
coelom
© 2011 Pearson Education, Inc.
Figure 32.9b
(b) Coelom
formation
Protostome development
(examples: molluscs,
annelids)
Deuterostome development
(examples: echinoderms,
chordates)
C
Coelom
Archenteron
c e te o
Coelom
Key
ey
Ectoderm
Mesoderm
Endoderm
Mesoderm
Blastopore
Solid masses of mesoderm
p and form coelom.
split
Blastopore
Mesoderm
Folds of archenteron
form coelom.
Fate of the Blastopore
• The blastopore forms during gastrulation and
connects the archenteron to the exterior of the
gastrula
• In protostome development, the blastopore
becomes the mouth
• In deuterostome development, the blastopore
b
becomes
th
the anus
© 2011 Pearson Education, Inc.
Figure 32.9c
(c) Fate of the
blastopore
Protostome development
(examples: molluscs,
annelids)
Deuterostome development
(examples: echinoderms,
chordates)
Anus
Mouth
Digestive tube
Key
Ectoderm
Mesoderm
Endoderm
Mouth
Mouth develops from blastopore.
Anus
Anus develops from blastopore.
Concept : New views of animal phylogeny
are emerging from molecular data
• Zoologists recognize about three dozen animal
phyla
• Phylogenies now combine morphological,
molecular, and fossil data
• Current debate in animal systematics has led to
the development
p
of multiple
p hypotheses
yp
about the
relationships among animal groups
© 2011 Pearson Education, Inc.
• One hypothesis of animal phylogeny is based
mainly on morphological and developmental
comparisons
© 2011 Pearson Education, Inc.
Figure 32.10
Porifera
Cnidaria
Eum
metazoa
M
Metazoa
ANCESTRAL
COLONIAL
FLAGELLATE
Ctenophora
Pro
otostomiia
Billateria
Deutero
ostomia
a
Ectoprocta
Brachiopoda
p
Echinodermata
Chordata
Platyhelminthes
R tif
Rotifera
Mollusca
Annelida
Arthropoda
Nematoda
• One hypothesis of animal phylogeny is based
mainly on molecular data
© 2011 Pearson Education, Inc.
Figure 32.11
Ct
Ctenophora
h
Eumeta
azoa
Me
etazoa
ANCESTRAL
COLONIAL
FLAGELLATE
Porifera
Cnidaria
Acoela
Bilateria
Chordata
Platyhelminthes
L
Lophotro
ochozoa
a Ecdysozoa
Deute
erostomiia
Echinodermata
Rotifera
Ectoprocta
Brachiopoda
Mollusca
Annelida
Nematoda
Arthropoda
Points of Agreement
1. All animals share a common ancestor
2. Sponges are basal animals
3 Eumetazoa
3.
E
t
is
i a clade
l d off animals
i l
(eumetazoans) with true tissues
4. Most animal phyla belong to the clade Bilateria,
and are called bilaterians
5. Chordates and some other phyla belong to the
clade Deuterostomia
© 2011 Pearson Education, Inc.
Progress in Resolving Bilaterian
Relationships
• The morphology-based tree divides bilaterians into
two clades: deuterostomes and protostomes
• In contrast, recent molecular studies indicate three
bil t i clades:
bilaterian
l d
D
Deuterostomia,
t
t i E
Ecdysozoa,
d
and
d
Lophotrochozoa
• Ecdysozoans shed their exoskeletons through a
process called ecdysis
© 2011 Pearson Education, Inc.
Vertebrate Development:
p
A Bodyy
Building Plan
• A human embryo
y at about 7 weeks after
conception shows development of distinctive
features
© 2011 Pearson Education, Inc.
Figure 47.1
1 mm
• Development occurs at many points in the life
cycle of an animal
• This includes metamorphosis and gamete
production, as well as embryonic development
© 2011 Pearson Education, Inc.
Figure 47.2
EMBRYONIC DEVELOPMENT
Sperm
Zygote
Adult
frog
Egg
Metamorphosis
Blastula
Larval
stages
Gastrula
Tail-bud
embryo
• Although animals display different body plans
plans,
they share many basic mechanisms of
development and use a common set of
regulatory genes
• Biologists use model organisms to study
development, chosen for the ease with which
they can be studied in the laboratory
© 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.
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
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 47.3-1
Basal body
(centriole)
p
Sperm
head
Acrosome
Jelly coat
Sperm-binding
receptors
Vitelline layer
Egg plasma membrane
Figure 47.3-2
Basal body
(centriole)
p
Sperm
head
Acrosome
Jelly coat
Sperm-binding
receptors
Hydrolytic enzymes
Vitelline layer
Egg plasma membrane
Figure 47.3-3
Sperm
nucleus
Basal body
(centriole)
p
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)
p
Sperm
head
Acrosome
Jelly coat
Sperm-binding
receptors
Acrosomal
process
Actin
filament
Fused
plasma
membranes
b
Hydrolytic enzymes
Vitelline layer
Egg plasma membrane
Figure 47.3-5
Sperm
plasma
membrane
Sperm
nucleus
Basal body
(centriole)
p
Sperm
head
Acrosome
Jelly coat
Sperm-binding
receptors
Fertilization
envelope
l
Acrosomal
process
Actin
filament
Cortical
Fused
granule
plasma
membranes
b
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
egg, vesicles
just beneath the egg plasma membrane release
their contents and form a fertilization envelope
• The fertilization envelope acts as the slow block
t polyspermy
to
l
© 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
• Ca
C 2 spread
d across th
the egg correlates
l t with
ith th
the
appearance of the fertilization envelope
© 2011 Pearson Education, Inc.
Figure 47.4
EXPERIMENT
10 sec after
fertilization
25 sec
35 sec
1 min
10 sec after
f tili ti
fertilization
20 sec
30 sec
500 m
RESULTS
1 sec before
f tili ti
fertilization
CONCLUSION
Point of sperm
nucleus
entry
Spreading
wave of Ca2
Fertilization
envelope
500 m
m
Figure 47.4a
EXPERIMENT
10 sec after
fertilization
25 sec
35 sec
1 min
10 sec after
fertilization
20 sec
30 sec
500 m
RESULTS
1 sec before
fertilization
500 m
Figure 47.4b
CONCLUSION
Point
P
i t off sperm
nucleus
entry
Spreading
wave of Ca2
Fertilization
envelope
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
l d presentt iin th
the egg
• The sperm nucleus merges with the egg nucleus
and cell division begins
© 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
Thi is
i called
ll d capacitation,
it ti
and
d mustt occur b
before
f
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
pellucida,
• No fast block to polyspermy has been identified in
mammals
l
© 2011 Pearson Education, Inc.
Figure 47.5
Zona pellucida
Follicle cell
Sperm
basal body
Sperm
nucleus
Cortical
granules
• In mammals the first cell division occurs 1236
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,
cleavage a period of
rapid cell division without growth
• Cleavage partitions the cytoplasm of one large cell
into many smaller cells called blastomeres
• The
Th blastula
bl t l is
i ab
ballll off cells
ll with
ith a flfluid-filled
id fill d
cavity called a blastocoel
© 2011 Pearson Education, Inc.
Figure 47.6
50 m
(a) Fertilized egg
(b) Four-cell stage (c) Early blastula
( ) Later blastula
(d)
Cleavage Patterns
• In frogs and many other animals
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
d vegetal
t lh
hemispheres
i h
th
thatt diff
differ iin appearance
© 2011 Pearson Education, Inc.
• The first two cleavage furrows in the frog form
four equally sized blastomeres
• The third cleavage is asymmetric
asymmetric, forming
unequally sized blastomeres
© 2011 Pearson Education, Inc.
• Holoblastic cleavage,
cleavage complete division of the
egg, occurs in species whose eggs have little or
moderate amounts of yolk
yolk, such as sea urchins
and frogs
• Meroblastic cleavage,
cleavage incomplete division of the
egg, occurs in species with yolk-rich eggs, such as
reptiles and birds
© 2011 Pearson Education, Inc.
Figure 47.7
Zygote
2-cell
2
ll
stage
forming
Gray crescent
0.25 mm
8-cell stage (viewed
f
from
the
h animal
i l pole)
l )
4-cell
stage
forming
8 cell
8-cell
stage
Animal
pole
0.25 mm
Blastula (at least 128 cells)
V
Vegetal
l pole
l
Blastula
(cross
section)
Blastocoel
Figure 47.7a-1
Zygote
Figure 47.7a-2
Gray crescent
Zygote
2-cell stage
forming
Figure 47.7a-3
Gray crescent
Zygote
2-cell stage
forming
4-cell stage
forming
Figure 47.7a-4
Animal pole
Gray crescent
Zygote
2-cell stage
forming
Vegetal pole
4-cell stage
forming
8-cell stage
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)
Figure 47.7b
0 25 mm
0.25
Animal
pole
8-cell stage (viewed
from the animal pole)
Figure 47.7c
0 25 mm
0.25
Blastocoel
Blastula (at least 128 cells)
Regulation of Cleavage
• Animal embryos complete cleavage when the ratio
of material in the nucleus relative to the cytoplasm
is sufficiently large
© 2011 Pearson Education, Inc.
Concept 47.2: Morphogenesis in animals
involves specific changes in cell shape,
position,
ii
and
d survival
i l
• After
f cleavage, the rate off 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 partl
partly fills the space bet
between
een the
endoderm and ectoderm
• E
Each
h germ llayer contributes
t ib t tto specific
ifi structures
t t
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
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
d ducts
d
• 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
th vegetal
the
t l pole
l and
db
buckles
kl iinward
d th
through
h
invagination
© 2011 Pearson Education, Inc.
• The newly formed cavity is called the
archenteron
• This opens through the blastopore,
blastopore which will
become the anus
© 2011 Pearson Education, Inc.
Figure 47.9
Animal
pole
Blastocoel
Mesenchyme
cells
Vegetal plate
Vegetal
g
pole
Blastocoel
Filopodia
Mesenchyme
cells
Bl t
Blastopore
Archenteron
50 m
Blastocoel
Ectoderm
Key
Future ectoderm
Future mesoderm
Future endoderm
Mouth
Mesenchyme
(mesoderm forms
future skeleton)
A h t
Archenteron
Blastopore
Di
Digestive
i tube
b (endoderm)
( d d
)
Anus (from blastopore)
Figure 47.9a-1
Blastocoel
Animal
pole
Mesenchyme
cells
Vegetal Vegetal
pole
plate
Key
Future ectoderm
Future mesoderm
Future endoderm
Figure 47.9a-2
Blastocoel
Animal
pole
Mesenchyme
cells
Vegetal Vegetal
pole
plate
Key
Future ectoderm
Future mesoderm
Future endoderm
Figure 47.9a-3
Blastocoel
Animal
pole
Mesenchyme
cells
Filopodia
Vegetal Vegetal
pole
plate
Archenteron
Key
Future ectoderm
Future mesoderm
Future endoderm
Figure 47.9a-4
Blastocoel
Animal
pole
Mesenchyme
cells
Filopodia
Vegetal Vegetal
pole
plate
Archenteron
Blastocoel
Archenteron
Key
Future ectoderm
Future mesoderm
Future endoderm
Blastopore
Figure 47.9a-5
Blastocoel
Animal
pole
Mesenchyme
cells
Filopodia
Vegetal Vegetal
pole
plate
Archenteron
Blastocoel
Archenteron
Key
Future ectoderm
Future mesoderm
Future endoderm
Digestive tube
(endoderm)
Ectoderm
Blastopore
Mouth
Mesenchyme
(mesoderm forms
future skeleton)
Anus
(from blastopore)
Figure 47.9b
Blastocoel
Filopodia
Mesenchyme
cells
Blastopore
Archenteron
50 m
Gastrulation in Frogs
• Frog gastrulation begins when a group of cells on
the dorsal side of the blastula begins to
invaginate
g
• This forms a crease along the region where the
gray
g
y crescent formed
• The part above the crease is called the dorsal lip
of the blastopore
p
© 2011 Pearson Education, Inc.
• Cells continue to move from the embryo surface
into the embryo by involution
• These cells become the endoderm and
mesoderm
• Cells
C ll on th
the embryo
b
surface
f
will
ill fform th
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
Bl
t
Yolk plug
Archenteron
Figure 47.10a
1
CROSS SECTION
SURFACE VIEW
Animal pole
Bl t
Blastocoel
l
Key
Future
ectoderm
Future
mesoderm
Future
endoderm
Dorsal
lip
p of
blastopore
Early
E
l
Vegetal pole
gastrula
Blastopore
Dorsal
lip of
blastopore
Figure 47.10b
2
Key
Future
ectoderm
Future
mesoderm
Future
endoderm
Blastocoel
shrinking
Archenteron
Figure 47.10c
3
Key
Future
ectoderm
Future
mesoderm
Future
endoderm
Late
gastrula
Blastopore
Blastocoel
remnant
Ectoderm
Mesoderm
Endoderm
Blastopore
Yolk plug
A h
Archenteron
Gastrulation in Chicks
• Prior to gastrulation,
gastrulation the embryo is composed of
an upper and lower layer, the epiblast and
hypoblast respectively
hypoblast,
• During gastrulation, epiblast cells move toward the
midline of the blastoderm and then into the
embryo toward the yolk
© 2011 Pearson Education, Inc.
• The midline thickens and is called the primitive
streak
• The hypoblast cells contribute to the sac that
surrounds the yolk and a connection between the
yolk and the embryo
embryo, but do not contribute to the
embryo itself
© 2011 Pearson Education, Inc.
Figure 47.11
Fertilized egg
Primitive
streak
Embryo
Yolk
Primitive streak
Epiblast
p
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
d off the
th blastocyst
bl t
t
• 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.
• Following implantation,
implantation the trophoblast
continues to expand and a set of
extraembryonic membranes is formed
• These enclose specialized structures outside of
the embryo
• Gastrulation involves the inward movement from
th epiblast,
the
ibl t th
through
h a primitive
i iti streak,
t k similar
i il
to the chick embryo
© 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)
(f
ibl t)
Chorion (from trophoblast)
4 Gastrulation has produced a
three-layered
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
yp
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
Ch
i (from
(f
trophoblast)
t
h bl t)
3 Extraembryonic membranes
start to form (10–11
(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
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.
• In both adaptations
adaptations, embryos are surrounded
by fluid in a sac called the amnion
• This
Thi protects
t t the
th embryo
b
ffrom desiccation
d i
ti and
d
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
Th yolk
The
lk sac encloses
l
th
the yolk
lk
The allantois disposes of waste products and
contributes
t ib t tto gas exchange
h
© 2011 Pearson Education, Inc.
Organogenesis
• During organogenesis,
organogenesis various regions of the
germ layers develop into rudimentary organs
• Early in vertebrate organogenesis
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
E t d
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
Figure 47.13a
Neural folds
1 mm
Neural Neural
fold
plate
Notochord
Ectoderm
Mesoderm
Endoderm
Archenteron
A
h t
(a) Neural plate formation
• The neural plate soon curves inward
inward, forming the
neural tube
• The neural tube will become the central nervous
system (brain and spinal cord)
© 2011 Pearson Education, Inc.
Figure 47.13b-1
(b) Neural tube formation
Neural
fold
Neural plate
Figure 47.13b-2
Neural
fold
Neural plate
Neural
crest cells
(b) Neural tube formation
Figure 47.13b-3
Neural
fold
Neural plate
Neural
crest cells
Neural
crest cells
(b) Neural tube formation
Neural
tube
Outer layer
y
of ectoderm
• Neural crest cells develop along the neural tube
of vertebrates and form various parts of the
embryo (nerves
(nerves, parts of teeth
teeth, skull bones
bones, and so
on)
• Mesoderm lateral to the notochord forms blocks
called somites
• Lateral
L t l tto the
th somites,
it
th
the mesoderm
d
splits
lit tto fform
the coelom (body cavity)
© 2011 Pearson Education, Inc.
Figure 47.13c
Eye
SEM
Neural tube
Notochord
Coelom
Somites
Tail bud
1 mm
Neurall
N
crest
cells
Somite
(c) Somites
Archenteron
(di
(digestive
ti
cavity)
Figure 47.13d
Neural folds
1 mm
Figure 47.13e
Eye
SEM
Somites
T il bud
Tail
b d
1 mm
• Organogenesis in the chick is quite similar to that
in the frog
© 2011 Pearson Education, Inc.
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
y organogenesis
g
g
Yolk sac
Neural
tube
YOLK
((b)) Late organogenesis
g
g
Figure 47.14a
Neural tube
Notochord
Somite
Archenteron
Coelom
Endoderm
Mesoderm
Ectoderm
Lateral
fold
Yolk stalk
These layers
form extraembryonic
membranes.
(a) Early organogenesis
Yolk sac
YOLK
Figure 47.14b
Eye
ye
Forebrain
Heart
Blood
vessels
Somites
Neural
tube
(b) Late organogenesis
• The mechanisms of organogenesis in
invertebrates are similar, but the body plan is very
different
• For example, the neural tube develops along the
ventral side of the embryo in invertebrats
invertebrats, rather
than dorsally as occurs in vertebrates
© 2011 Pearson Education, Inc.
Mechanisms of Morphogenesis
• Morphogenesis in animals but not plants involves
movement of cells
© 2011 Pearson Education, Inc.
The Cytoskeleton in Morphogenesis
• Reorganization of the cytoskeleton is a major force
in changing cell shape during development
• For example,
example in neurulation,
neurulation microtubules oriented
from dorsal to ventral in a sheet of ectodermal
cells help lengthen the cells along that axis
© 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
• Thi
This iis convergentt extension,
t
i
th
the
rearrangement of cells of a tissue that cause it to
become narrower (converge) and longer (extend)
• Convergent extension occurs in other
d
developmental
l
t l 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
cells,
cells, or whole tissues stop
developing and are engulfed by neighboring cells
• For example,
example many more neurons are produced in
developing embryos than will be needed
• Extra neurons are removed by apoptosis
© 2011 Pearson Education, Inc.
• 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 affter fertilization (h
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))
g
Musculature
Hatching
g
Intestine
Intestine
Anus
Mouth
Eggs
Vulva
POSTERIOR
ANTERIOR
1.2 mm
Figure 47.18a
• Germ cells are the specialized cells that give rise
to sperm or eggs
• Complexes of RNA and protein are involved in the
specification of germ cell fate
• In
I C.
C elegans,
l
such
h complexes
l
are called
ll d P
granules, persist throughout development, and
can be
b d
detected
t t d iin germ cells
ll off th
the adult
d lt worm
© 2011 Pearson Education, Inc.
Figure 47.19
100 m
• P granules are distributed throughout the newly
fertilized egg and move to the posterior end before
the first cleavage division
• With each subsequent cleavage, the P granules
are partitioned into the posterior-most cells
• P granules act as cytoplasmic determinants, fixing
germ cellll ffate
t att the
th earliest
li t stage
t
off development
d
l
t
© 2011 Pearson Education, Inc.
Figure 47.20
20 m
1 Newly fertilized egg
2 Zygote prior to first division
3 Two-cell embryo
4 Four-cell embryo
Axis Formation
• A body plan with bilateral symmetry is found
across a range of animals
• This body plan exhibits asymmetry across the
dorsal-ventral and anterior-posterior axes
• The
Th right-left
i ht l ft axis
i iis llargely
l symmetrical
ti l
© 2011 Pearson Education, Inc.
• The anterior
anterior-posterior
posterior axis of the frog embryo is
determined during oogenesis
• The animal-vegetal
animal vegetal asymmetry indicates where
the anterior-posterior axis forms
• The
Th d
dorsal-ventral
l
t l axis
i iis nott d
determined
t
i d until
til
fertilization
© 2011 Pearson Education, Inc.
• Upon fusion of the egg and sperm
sperm, the egg
surface rotates with respect to the inner cytoplasm
• This cortical rotation brings molecules from one
area of the inner cytoplasm of the animal
hemisphere to interact with molecules in the
vegetal cortex
• This
Thi lleads
d tto expression
i off d
dorsall and
d ventralt l
specific gene expression
© 2011 Pearson Education, Inc.
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
• In chicks,
chicks gravity is involved in establishing the
anterior-posterior axis
• Later,
Later pH differences between the two sides of the
blastoderm establish the dorsal-ventral axis
• In
I mammals,
l experiments
i
t suggestt that
th t orientation
i t ti
of the egg and sperm nuclei before fusion may
h l establish
help
t bli h embryonic
b
i axes
© 2011 Pearson Education, Inc.