Transcript Embryonic development

Embryonic development
Embryonic development of the nematode C. elegans
4 main stages on the growth and development of animals.
1. Gametogenesis
•
Formation of sperm and egg
•
Begins with fertilization and ends with birth
•
Process leading to reproductive maturity (puberty)
2. Embryonic Development
Video
3. Maturation
4. Aging
--We will concentrate on Embryonic Development--
Stages of Embryonic development
1.
2.
3.
4.
5.
6.
7.
Fertilization
Cleavage
Morulation
Blastulation
Gastrulation
Extraembryonic membrane development
Organogenesis
Fertilization
1. Acrosomal
reaction
(recognition)
2. Penetration
3. Cortical
reaction
4. Activation of
egg
Acrosom
al
Animatio
n
1
2
3
4
6
8
10
20
30
40
50
1
Binding of sperm to egg
Acrosomal reaction: plasma
Membrane depolarization
(fast block to polyspermy)
Increased intracellular calcium level
Cortical reaction begins
(slow block to polyspermy)
Formation of fertilization envelope complete
2
Increased intracellular pH
3
4
5
Increased protein synthesis
10
20
Fusion of egg and sperm nuclei complete
30
40
Onset of DNA synthesis
60
90
First cell division
1-The acrosomal reaction
–
–
Head of sperm (acrosome) releases hydrolytic enzymes that penetrate the
jelly coats of the egg.
Sperm releases proteins that bind to receptors on vitelline membrane of
the egg.
2- Penetration
•
1
This ensure same species fertilization
2
4
3
Acrosomal reaction.
Contact.
Hydrolytic enzymes released from
the acrosome make a hole in the
jelly coat. Growing actin
filaments protrude from the sperm
head and penetrates the jelly coat,
Binding to receptors in the egg cell
membrane that extend through
the vitelline layer.
5
Entry of
sperm nucleus.
The membrane becomes
depolarized, resulting in the
fast block to polyspermy.
Sperm plasma
membrane
Sperm
nucleus
Acrosomal
process
Basal body
(centriole)
Fertilization
envelope
Sperm
head
Actin
Acrosome
Jelly coat
Sperm-binding
receptors
Fused plasma
Cortical membranes
granule
Perivitelline
Hydrolytic enzymes
space
Cortical granule
membrane
Vitelline layer
Egg plasma
membrane
EGG CYTOPLASM
Mammals
• Follicle cells are release with egg
• Sperm must find way through the cells to the “Zone
Pellucida”
• Sperm contain receptor molecules to move through the Zone
Follicle
cell
Zona pellucida
Egg plasma
membrane
Acrosomal
vesicle
Sperm
basal Sperm Cortical
body nucleusgranules
EGG CYTOPLASM
3- The cortical reaction
–
–
The fusion sets up a signal transduction pathway that cause large
amts of Ca2+ to be release into cytoplasm
Ca2+ cause change in cortical granules causing hardening of
membrane
•
1
This resist the entry of any other sperm
2
4 Entry of
sperm nucleus.
3
5
Cortical reaction.
cytosol, causing cortical granules
Fusion of sperm
and egg membranes.
Contact
Acrosomal reaction.
This in
leads
totoswelling
of plasma
the
the egg
fuse with the
perivitelline
space,
hardening
membrane
and discharge
their of the
contents.
Thisand
leadsclipping
to swelling
vitelline
layer,
ofof the
perivitelline
space,
hardening
of
sperm-binding receptors. Thetheresulting
vitelline layer, and clipping of
fertilization
envelope is the slow block
sperm-binding receptors. The resulting
to polyspermy.
fertilization envelope is the slow block
to polyspermy.
Sperm plasma
membrane
Sperm
nucleus
Acrosomal
process
Basal body
(centriole)
Fertilization
envelope
Sperm
head
Actin
Acrosome
Jelly coat
Sperm-binding
receptors
Fused plasma
Cortical membranes
granule
Perivitelline
Hydrolytic enzymes
space
Vitelline layer
Egg plasma
membrane
EGG CYTOPLASM
Cortical granule
membrane
Hypothetical pathway for calcium release
Fertilization Overview



4.
Acrosomal reaction (recognition)
Penetration
Cortical reaction
Activation of egg
Polar body discharged
–
–
Sharp rise in Ca2+ causes the egg to begin to develop
Humans- completion of Meiosis II.
–
–
Sperm and egg nuclei fuse
Substantial increase in the rates of cellular respiration
and protein synthesis by the egg cell
•
Polar body are discharged through membrane
Parthenogenesis
• Development of an
unfertilized egg.
• Drone honey bees
develop by natural
parthenogenesis
Haploid males
Stages of Embryonic development
1. Fertilization
.
2.
3.
4.
5.
6.
7.
Cleavage
Morulation
Blastulation
Gastrulation
Extraembryonic membrane development
Organogenesis
Cleavage
• Cleavage partitions the cytoplasm of one large cell
–
Into many smaller cells called blastomeres
Fertilized egg.
Shown here is the
zygote shortly
(a)
before the first
cleavage division,
surrounded by the
fertilization
envelope. The
nucleus is visible
in the center.
Four-cell stage.
(b)Remnants of the
mitotic spindle can
be seen between
the two cells that
have just completed
the second cleavage
division.
(c)
Morula. After
Blastula. A
single layer of cells
surrounds a large
further cleavage
(d)blastocoel cavity.
divisions, the embryo is a
Although not visible
multicellular ball that is
here, the fertilization
still surrounded by the
envelope is still
fertilization envelope.
present; the embryo
The blastocoel cavity has
will soon hatch from
begun to form. (12 cells)
it and begin
swimming.
Blastulation
•Cleavage results in the formation of a multicellular stage called a blastula.
•The blastula of many animals is a hollow ball of cells
Blastocoel
Cleavage
Cleavage
Eight-cell stage
Zygote
Blastocoel
Endoderm
Ectoderm
Gastrula
Blastopore
Gastrulation
Blastula
Cross section
of blastula
Blastulation & Gastrulation
Blastocoel
Eight-cell stage
Zygote
-cavity
of the
blastula
Cleavage
Cleavage
Blastocoel
Blastula
Cross section
of blastula
Endoderm
Ectoderm
Gastrula
Blastopore
Gastrulation
Gastrulation
Animation
•A rearrangement of the embryo in
which one end of the embryo folds
inward, expands, and eventually fills
the blastocoel
•The three layers produced by
gastrulation
Frog Blastula
Gastrulation
• The three layers produced by gastrulation
• Archentron
• Blastopore
– Mouth or
anus
Archenteron
(primitive gut)
Gastrulation in a
sea urchin
Key
Future ectoderm
Future mesoderm
Future endoderm
Mesenchyme
cells
Vegetal
plate
Animal
pole
Blastocoel
Vegetal
pole
Blastocoel
Filopodia
pulling
archenteron
tip
Archenteron
Blastopore
Mesenchyme
cells
Blastocoel
50 µm
Archenteron
Ectoderm
Mesenchyme:
(mesoderm
forms future
skeleton)
Mouth
Blastopore
Digestive tube (endoderm)
Anus (from blastopore)
Extraembryonic membrane development
• Birds, reptiles, & mammals.
– Develop within a fluid-filled sac that is
contained within a shell or the uterus
– Called amniotes
• Extraembryonic membranes develop
outside the embryo proper:
–
–
–
–
Chorion
Allantois
Amnion
Yolk sac
–Amnion
–Chorion
Allantois
Yolk sac
Amnion. The amnion protects
the embryo in a fluid-filled
cavity that prevents
dehydration & cushions
mechanical shock.
Allantois. The allantois functions as a disposal
sac for certain metabolic wastes produced by
the embryo. The membrane of the allantois
also functions with the chorion as a respiratory
organ. (placenta in mammals)
Embryo
Amniotic
cavity with
amniotic
fluid
Shell
Chorion. The chorion and the
membrane of the allantois
exchange gases between the
embryo and the surrounding
air. Oxygen and carbon dioxide
diffuse freely across the egg’s
shell.
Albumen
Yolk sac. The yolk sac
expands over the yolk, a
stockpile of nutrients
stored in the egg.
Blood vessels in the yolk
sac membrane transport
Yolk
nutrients from the yolk
(nutrients) into the embryo.
Other nutrients are
stored in the albumen
(the “egg white”).
Amniotic Egg
A critical evolutionary
development for
terrestrial animals is
the reptilian amniotic
egg, now also
characteristic of birds
and some mammals.
The developing embryo, protected from drying out, can survive
outside of water and in a variety of habitats. The yolk
provides it with food, and the albumin supplies water and
nutrients. Wastes are released to the allantois, an extension
of the embryonic gut. Oxygen diffuses easily through the
thin outer shell of the egg; its passage to the embryo is
regulated by the chorion.
Human
1. Decidua capsularis
2. Uterine wall
3. Uterine cavity
4. Placenta
5. Decidua parietalis
6. Decidua basalis
7. Chorion leave
8. Embryo
9. Connecting stalk
10. Yolk sac
11. Chorion
12. Amnion
13. Chorionic cavity
14. Amniotic cavity
Organogenesis
• Process by which cells
continue to
differentiate, producing
organs from the three
embryonic germ layers.
• Three kinds of
morphogenetic changes
Neural
Neural plate
fold
First to
form-the
neural tube
– Folds
– Splits
– Dense clustering
(condensation)
Neural
crest
Neural
crest
Neural tube
Figure 47.14b
Outer layer
of ectoderm
(b)Formation of the neural tube.
Infolding and pinching off of the
neural plate generates the neural
tube. Note the neural crest cells,
which will migrate and give rise to
Numerous structures.
• Early in
vertebrate
organogenesis
–
The
notochord
forms from
mesoderm
and the
neural plate
forms from
ectoderm
Figure 47.14a
Neural folds
LM
1 mm
Neural
fold
Neural
plate
Notochord
Ectoderm
Mesoderm
Endoderm
Archenteron
(a) Neural plate formation. By the time
shown here, the notochord has
developed from dorsal mesoderm,
and the dorsal ectoderm has
thickened, forming the neural plate,
in response to signals from the
notochord. The neural folds are
the two ridges that form the lateral
edges of the neural plate. These
are visible in the light micrograph
of a whole embryo.
Chick
Organogenesis
Factors that Influence Embryonic Development
1. Cytoplasmic Determinants
(who’s gonna be what)
 differently differentiated cell lineages


Uneven cytoplasmic distribution
Substances that are inherited during cleavage set “stage” for
development
 proteins as well as mRNAs found in the cytoplasm
 Location during cleavage can also play a role
2. Embryonic Induction
(cell signaling)
 Ability of one group of embryonic cells to influence the
development of another group of embryonic cells
3. Homeotic, Homoeobox, or Hox Genes
 MASTER genes that control the expression of genes
responsible for specific anatomical structures.
Fish, Frogs,
Birds and
Humans
Classic studies using frogs
-Gave indications that the lineage of cells
making up the three germ layers created
by gastrulation is traceable to cells in the
Epidermis
blastula
Central
nervous
system
Epidermis
Notochord
Mesoderm
Endoderm
Blastula
(a)
Neural tube stage
(transverse section)
Fate map of a frog embryo. The fates of groups of cells in a frog blastula (left) were
determined in part by marking different regions of the blastula surface with nontoxic dyes
of various colors. The embryos were sectioned at later stages of development, such as
the neural tube stage shown on the right, and the locations of the dyed cells determined.
Later studies
-Marked individual blastomeres during cleavage and then followed it
through development
Cell lineage analysis in a tunicate. In lineage analysis, an individual
(b) cell is injected with a dye during cleavage, as indicated in the drawings
of 64-cell embryos of a tunicate, an invertebrate chordate. The dark
regions in the light micrographs of larvae correspond to the cells that
developed from the two different blastomeres indicated in the
drawings.
Subcortical Rotation and the "Gray Crescent"
-Formation of the
grey crescent of
the amphibian egg.
-The dense, yolky
vegetal deep
cytoplasm rotates
with respect to
the overlying
cortex.
Gray crescent - Region of intermediate
pigmentation in the marginal zone of the
amphibian egg caused by a shift in the
pigmented egg cortex toward the
site of sperm entry; marks the future
site of the dorsal lip of the blastopore.
Website
•Development of embryo occurs in a flat disc (blastodisc) that sits on top
of the yolk.
•A primitive streak forms instead of a gray crescent.
•Cells migrate over the primatitive strek and flow inward to form the
archentron.
•Extraembryonic membranes form.
A human embryo at approximately 6–8
weeks after conception
1 mm
• Early
embryonic
development in
a human
–
Endometrium
(uterine lining)
Inner cell mass
Trophoblast
Blastocoel
Proceeds
through four
stages
Expanding
region of
trophoblast
Maternal
blood
vessel
Epiblast
Hypoblast
Trophoblast
1 Blastocyst
reaches uterus.
Expanding
region of
trophoblast
Amniotic
cavity
Amnion
Epiblast
2 Blastocyst
implants.
Extraembryonic
3 membranes
start to form and
gastrulation begins.
Hypoblast
Chorion (from
trophoblast)
Extraembryonic mesoderm cells
(from epiblast)
Allantois
Yolk sac (from
hypoblast)
Amnion
Chorion
Ectoderm
Mesoderm
Endoderm
Gastrulation has produced a three4
layered embryo with four
extraembryonic membranes.
Yolk sac
Extraembryonic
mesoderm
4 weeks
6
weeks