Gastrulation cont.

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Gastrulation cont.
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Organogenesis

• it is not birth, marriage or death, but
  gastrulation that is truly the most important
  time in your life
• What are fates of germlayers?

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Ectoderm
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Mesoderm
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Endoderm
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Modes of cell movements in Gastrulation

• Invagination (amphioxus)
• Involution (Amphibian)
• Ingression (Chick, mammals)
• Combo (involution and Ingression, zebrafish)

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Amphioxus Gastrulation
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Zebrafish gastrulation
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Zebrafish Gastrulation
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Teleost Gastrulation
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Amphibian gastrulation
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Amphibian Gastrulation
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Chick Gastrulation
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Mammalian Gastrulation
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Organogenesis

• it is not birth, marriage or death, but
  gastrulation that is truly the most important
  time in your life
• Gastrulation puts germ layers in proper
  orientation to one another, allows for inductive
  interactions
• Skin
• Epidermis (ectoderm)
• Dermis (mesoderm)

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The organizer

• Referred to as
• Embryonic shield
• Kohlers Sickle
• Organizer
• Node
• Usually present near dorsal-caudal end of
  gastrulation
• Established Dorsal/Ventral fates, directs
  gastrulation and A/P fates.
• Experimental movement of organizer caused second
  body axis to form

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Conservation of Organizer

• Organizer forms at the junction between two
  signalling pathways, Wnt and TGF-beta, in all
  vertebrates

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Neural Crest Cells
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Neural Crests and Placodes

• 4th germ layer
• Evolutionarily gives rise to skull
• Synapomorphy of craniates
• Arise at junction between neural fold and
  presumptive epiderm
• Cells delaminate from neural fold before closure
• Migrate and give rise to many tissues.

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