Epithelial and mesenchymal organization represent two major tissue types in animals.

1
ICQs class 15

• Epithelial and mesenchymal organization represent
  two major tissue types in animals.
• 1. Which of the following statements correctly
  characterize epithelial or mesenchymal cells? .5
  pts
• Cells are motile.
• Cells are similar and regular in shape.
• Cells can communicate with each other through gap
  junctions.
• Cells are not in contact, separated by
  extracellular matrix.

• i and ii are epithelial, iii and iv are
  mesenchymal
• ii, ii, iv are epithelial, iii is mesenchymal
• i, ii, iii are epithelial, iv is mesenchymal
• i and iii are epithelial, ii and iv are
  mesenchymal
• ii and iii are epithelial, i and iv are
  mesenchymal

2
Xenopus fate map
2. By what embryonic stage are all these fates
determined? a. Before fertilization b. At
fertilization c. Before gastrulation begins d. By
the middle-end of gastrulation e. After
gastrulation is complete
G 10.5
3
3. Which mesodermal precursor cells enter the
blastopore first in Xenopus gastrulation? a.
presumptive head (anterior) mesoderm b.
presumptive tail (posterior) mesoderm.
4. The bottle cells that initiate involution at
the blastopore are (.5 pts) a. presumptive
ectodermal cells. b. presumptive mesodermal
cells. c. presumptive endodermal cells.
4
ICQs Class 16

• (.5 pts) In the frog embryo, different kinds of
  mesoderm migrate into the embryo as gastrulation
  progresses (dorsal, then intermediate, then
  ventral). What about chick?a. its the sameb.
  its similar, but there is much more of an A-P
  gradientc. the mesoderm doesnt migrate inside
  during chick gastrulation, but the ectoderm does

5

• 2. Using the figures above, decide why the early
  isolated animal caps did not make neural cells.
• Chordin and noggin must be present in the early
  stage animal cap
• Chordin and noggin are not present in the early
  stage animal cap but BMPs are
• The animal cap cells are initially fated to be
  epidermis that fate is changed to neural
  ectoderm because of inductive events during
  gastrulation
• The animal cap cells can no longer be inhibited
  by BMPs after gastrulation

6

• 3. (.5) If you laser-ablated one of the cells
  (red) beginning to delaminate and form a
  neuroblast, what is the most likely fate of the
  cell next to it (indicated with an arrow)?
• It will become an epidermal cell
• It will become a neuroblast
• Its fate is already determined so it doesnt
  matter what you do

• 4. The notochord (chord of cells underlying the
  neural tube) is composed of
• Cells from the organizer
• Cells from the Niewkoop center
• Ectodermal cells from the animal cap
• Endodermal cells derived from the bottle cells

7
Adhesion molecules play a role in separation
of neural tube from overlying epidermis
What would happen if you were to inject
N-cadherin into the cells that normally make the
surface ectoderm before neurulation? neurulation
begins but cannot complete
8

• The risk for neural tube defects is two to five
  times higher than normal if a mother has
  diabetes.
• Why?
• Data
• pax-3 -/- homozygous mutant mice are born with
  neural tube defects
• Diabetic mice have low pax-3 levels
• pax-3 interacts with p53 (remember the role of
  p53?)

Work with your group to propose a role for how
pax-3 and p53 might be involved in neural tube
defects Can you draw a pathway?
Pax-3 and p53 double mutants did not have neural
tube defects
High blood sugar -- Pax-3 -- p53 ? cell
death Low pax-3 leads to activated p53 leads to
cell death leads to neural tube closure defect