Early Development
Selected Invertebrates
Cleavage

What characterizes this process?
Cleavage

How does the cell cycle of blastomeres compare
with that of somatic cells?
Cleavage

What happens to the embryo during the
mid-blastula transition?

When does this occur?
Cleavage

What is karyokinesis and cytokinesis and how do
they compare?
Cleavage

What influences the pattern of cleavage in
a particular organism?
Cleavage
Cleavage
Cleavage

How are cell fates specified during
cleavage?
– cell-cell interactions
– asymmetric distribution of morphogenic
determinants
Gastrulation
What characterizes gastrulation in organisms?
 What kinds of movements occur?

Axis Formation

What are the three major body axes?
Sea Urchin Development

What does the cleavage pattern look like?
Sea Urchin Development

What characterizes the blastula stage?
Sea Urchin Development

At what stage are the fates of individual cells
determined?
Sea Urchin Development

What role does βcatenin play in
specification?
Sea Urchin Development
Sea Urchin Development

When does axis specification occur?
– animal-vegetal axis established before
fertilization
– anterior-posterior axis determined by a-v axis
 vegetal – determinants for posterior development
– dorsal-ventral and left-right after fertilization
 d-v by first cleavage plane
Sea Urchin Development

How does gastrulation
begin?
Sea Urchin Development

What appears to be responsible for the
ingression of primary mesenchyme?
Sea Urchin Development

What appears to be responsible for the initial
invagination that occurs during gastrulation?
Sea Urchin Development
What is the fate of these vegetal plate cells?
Sea Urchin Development

What happens during later stages of
invagination?
Sea Urchin Development
Snail Development

What kind of cleavage pattern characterizes
these animals?
Snail Development

Orientation of
cleavage plane
determines right or
left coiling snails
Snail Development

What appears to be responsible for the mosaic
development seen in molluscs?
Snail Development

What is the polar lobe and why is it important?
Snail Development

Why does removal of the D blastomere or
its first or second derivatives result in
incomplete larvae?

If D blastomeres don’t directly contribute
cells to formation of many structures why
are they so important to the formation of
the same structures?
Snail Development

What other aspect of snail development
does the polar lobe influence?
– How do we know this to be true?
Snail Development

How does gastrulation take place in snails?
Tunicate Development
What makes these
organisms rather
unique?
 What type of cleavage
pattern do they have?

Tunicate Development

In what way does the pigmentation in Styela
partita provide developmental information?
Tunicate Development

What evidence is there of autonomous
specification in tunicate blastomeres?
– transplant experiments
– RNA hybridization experiments
– altering β-catenin levels in cells
Tunicate Development

What evidence is there for conditional
specifiction?
– BMP signal from endoderm induces anterior
cell to become notocord
 works through activation of Brachury gene
– FGF signal induces posterior cell to become
mesenchyme
Tunicate Development

When are the
embryonic axes
established?
– dorsal-ventral – prior
to first cleavage
– anterior-posterior –
prior to first cleavage
– left-right – first
cleavage
Tunicate Development

What is gastrulation
like in these
organisms?
Caenorhabditis elegans

What does C. elegans look like?
C. elegans

What pattern of cleavage in seen in this
nematode?
C. elegans
C. elegans

What determines
anterior-posterior
axis?

What is the
importance of the Pgranules?
C. elegans

When is dorsal-ventral and left-right axes
established?
C. elegans

In what way is autonomous specification
demonstrated in this organism?
– P1 develops without presence of AB cell

In what way is conditional specification
demonstrated?
– AB cell requires cell-cell interactions
– EMS requires signal from P2
C. elegans

cell-cell signaling
C. elegans

Where in this organism is autonomous and
conditional specification integrated?
C. elegans

When does
gastrulation begin in
this organism?