01-17-03
Animal Development II
Making an embryo…
Where were we
 Remember
gametogenesis
Spermatogenesis
 Oogenesis

Back to fertilization
 What
are model organisms?
 What
are the models for studying
fertilization?
 The
rules of engagement…(fig 60.3)
What does the sperm encounter first?
 How can it get through the jelly coat?

More about fertilization
 What
is penetration (aka. the
acrosome reaction)? (fig 60.3)

Remember the acrosome?


Remember the jelly coat/zona pellucida?
What happens when the acrosome
encounters jelly coat?
What are the signals?
 What are hydrolytic enzymes?
 What do they do?

More about fertilization
 More

How does the sperm penetrate jelly
coat?


What is the acrosomal process
What happens at the vitelline
membrane?


acrosomal reaction…
Why are receptors important?
What happens next?
Sperm and egg membranes fuse
 HOORAY!!!

Fig 60.3
More about fertilization
 What
is the situation?
How many eggs are available?
 How many sperm are available?
 Only ONE winner!

 What
is polyspermy?
 How is polyspermy prevented?
Fast block to polyspermy
 Slow block to polyspermy

The fast block to
polyspermy
 What
is membrane potential?
 What happens to the membrane
potential upon sperm fusion?
 How does depolarization prevent
polyspermy?
 How long does the fast block to
poplyspermy last?
The slow block to
polyspermy
 How

does the slow block work?
What is signal transduction?
What are second messengers?
 Why do we need them?

More about the slow block
 Where
are intracellular Calcium
stores?
How is calcium release triggered?
 How does it radiate over surface of
egg?


Doing the Calcium wave…

http://sdb.bio.purdue.edu/dbcinema/
Campbell fig 47.3
More about the slow block
 What
does calcium release do?
Cortical granules fuse with PM
 Release contents into perivitelline
space

 What
are cortical granules?
Where are they located?
 What do they contain?

enzymes
 mucopolysacchariddes

More about the slow block
 What
do mucopolysaccharides do in
perivitelline space?
Remember osmosis?
 How do mucopolysaccharides affect
osmolarity?
 What does this do to perivitelline
space?

More about the slow block
 What
do the enzymes from cortical
granules do?
What happens when polysaccharides
become crosslinked?
 How would this affect sperm
penetration?

 How
long does all of this take?
Let’s talk about cleavage!
 What
is cleavage?
How often does it occur?
 Does the zygote increase in size?
 What are blastomeres?

More about cleavage
 What
effect does yolk have on
cleavage?
Isolecithal
 Mesolecithal
 Telolecithal

isolecithal
mesolecithal
telolecithal
More about cleavage
 What
types of cleavage are there?
What is holoblastic cleavage?
 What is meroblastic cleavage?
 What is superficial cleavage?

More about cleavage
 What
about the cleavage plane?
 What is the polarity of an organism?
How is oocyte polarity established?
 How are embryonic axes determined?

Remember cytoplasmic determinants?
 What does sperm entry do?
 What is cortical rotation?


How does the cleavage plane compare
with embryonic axes in frogs? (fig 60.4)
A
P
cleavage
More about polarity?
 How
is embryonic polarity
determined in other organisms?

How do Drosophila establish polarity
Remember cytoplasmic determinants
again?
 Sperm entry is controlled


What is the micropile
Opposing gradients
 Cascading signaling

More about polarity
 How
is polarity established in
mammals?

What does sperm entry do?

Remember egg activation
Does sperm entry affect cleavage
plane?
 What is the polarity of a mammalian
embryo?


Embryonic  abembryonic

Remember the trophoblast/inner cell mass
From: Plotrowska and Zernicka-Goetz (2001) Nature 409:517-21
More about cleavage
 Radial
vs. spiral cleavage
Radial cleavage aligns animal cells with
vegetal cells
 Spiral cleavage offsets animal cells
from vegetal cells

 How
does cleavage relate to
phylogeny of coelomates?
Deuterostomes  radial cleavage
 Protostomes  animal cleavage

Fig 44.5
More about cleavage
 More
cleavage  morula (mulberry)
 Morula
 blastula
Hollow ball of cells
 Cavity called blastoceol

Blastula stage
Tissue formation
 What

are triploblastic organisms?
What are the three basic tissue layers?
Remember ectoderm?
 Remember mesoderm?
 Remember endoderm?

 How

are the three layers generated?
What is gastrulation?
Sea urchin
gastrulation
• Mesenchyme
• Vegetal plate
• Blastopore
Campbell Fig 47.9
More about gastrulation
 What
effect does yolk have on
gastrulation?

Mesolecithal organisms (e.g. frogs)
What is the dorsal lip?
 What happens to the blastocoel?

Gastrulation in frogs
Fig 60.11
More about gastrulation
 What
about gastrulation in
telolecithal organisms (e.g. chicks)

Where are the blastocysts located?
Remember meroblastic cleavage?
 What is the blastodisc?


How can three cell layers come from
two?
Where is the epiblast?
 Where is the hypoblast?


What is the primitive streak?
Fig 60.12
What about mammals?
 How
much yolk do mammalian eggs
have?
 How are blastocysts organized?
What is the trophoblast layer?
 What is the inner cell mass
 Which cells give rise to the embryo
proper?

 How
do mammals compare with
birds?
Mammalian gastrulation
 How
does gastrulation proceed in
mammalian embryos?
What is the amniotic cavity?
 What are the extraembryonic
membranes?



Remember the trophoblast layer?
Where does the mesoderm come from?

Remember the primitive streak in birds?
Gastrulation summary
 What
is the overall goal of
gastrulation

Remember three tissue layers
 What
are the challenges?
Yolk content
 Blastocyst arrangement

 What
are the mechanisms
Cell shape changes
 Cell location changes

What have we learned
 Next

day:
Organogenesis and limb formation