Gastrulation

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Gastrulation

• Differentiating the embryo into 3 germ layers
• Endoderm on the inside
• Ectoderm on the outside
• Mesoderm in the middle

2
The ectoderm makes up the following

• The central nervous system
• The epidermis of the skin
• The adrenal medulla
• A and B
• All of the above

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Gastrulation Movie
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Gastrulation - Zebrafish

• Animal Pole contains the nucleus and most of the
  cytoplasm.
• Vegetal Pole containing much yolk and little
  cytoplasm.

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Gastrulation - Zebrafish

• Epiboly starts thinning of the blastoderm,
  spreading over the yolk cell.

6
Gastrulation - Ingression

• First prospective mesendodermal cells ingress,
  forming the axial (shield, sh) and paraxial
  mesendodermal (apm) tissue.
• Cells migrate anteriorly (am) towards the animal
  pole.

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Gastrulation - Convergent extension

• Ectodermal and mesendodermal cells drive the
  progressive medio-lateral narrowing and anterior
  posterior extension of the emerging embryonic
  body axis.
• Anterior (apm) and Posterior (ppm) domains
• Notochord (not)

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Gastrulation Mechanisms
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Convergent Extension
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Convergent extension of the Archenteron
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What cellular characteristics would you expect of
mesenchymal cells?

• Apical surface
• Tight junctions
• Gap junctions
• Communicate through extracellular matrix
• C and D

12
Mesenchymal cells are unique from epithelial
cells in that

• They come from separate stem cells
• They contain no ability to form junctions
• They are motile
• B and C
• All of the above

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Epithelium
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Cadherins
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Cadherins Ca2 and RhoA
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Mesenchyme

• Transition from epithelial to mesenchymal

Mesenchymal cells will eventually become mesoderm
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Ingression
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Epithelia to Mesenchyme Transition
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Are the cells that convergently extend epithelial
or mesenchymal?

• Epithelial
• Mesenchymal
• Both
• None of the above

20
Cannonical Wnt pathway

• The default pathway of Cannonical Wnt activation
  leads to tail development.
• Also known as the Wnt/Beta-catenin pathway

Tail Development
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Dkk and LRP5/6

• Dkk sequesters LRP5/6 and promotes their
  internalization to lysosomes.

22
Extra cellular ligands are transmitted through
the cell in a process known as cellular
transduction, which of the following statements
is true?

• One ligand corresponds to one transducted
  message.
• Each ligand can only be inhibitory or activating.
• Message strengths can increase as the message is
  transducted.

23
During Gastrulation which signal(s) gives rise to
anterior neural developement?

• Wnt
• PCP
• Dkk
• None of the above

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Planar Cell Polarity (PCP) Pathway
Dkk1
Paper finds that Dkk1 activates the PCP through
Kny/Glypican6
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Glypican4/6 Knypek

• Glypican4/6 Knypek is Heparan sulfate
  proteoglycan (HSPG) activates the Wnt ligand to
  the Frizzled receptor to increase activation of
  the PCP Pathway.

Dkk1
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Wnt Signaling Pathway
Dkk1
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The End
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PCP and Core Factors
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Subcellular Distribution of Fz/PCP
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PCP and polarization
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PCP and zebrafish development
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Fz/PCP driven Cell Motility
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Cell Movements Separate
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Wnt Pathway
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Gene expression in neural plate