Early Vertebrate Development• Axis Determination• Amphibian Early Development: Frog• Fish Early Development: Zebra Fish
Heads or Tails? Axis specification • Common theme in early
development• Conserved mechanisms• Divergent mechanisms
Early Vertebrate Development: Xenopus
Xenopus: Cleavage• Sperm entry point:
Dorsal-Ventral (D-V) axis• Microtubule array• Cortical rotation.
Xenopus: Cleavage• Radially Symmetrical; Holoblastic• High amount of yolk in vegetal half.• Second cleavage before first finishes.• Third= equatorial• 16-64 cell stage: Morula• 128 cell stage: Blastula
Mid-Blastula Transition• DNA demethylation• H3K4 methylated (trimethylation) transcription activation• Ex. Vegetal cells endoderm. Produce paracrine factors that
induce mesoderm specification of cells above.
Xenopus: Gastrulation• Same goals as other organsims: get cells to appropriate
locations!• Movements start in Gray Crescent, cells invaginate to form
slit-like blastopore.
Xenopus Gastrulation: Involution
Vegetal Rotation: Movement of Pharyngeal endoderm above involuting mesoderm.
Involuting Marginal Zone (IMZ)
Xenopus: Gastrulation
Xenopus Gastrulation: Convergent extension
Axis specification in Xenopus: Induction• Animal-Vegetal axis
determines tissue type• A-V, D-V, and L-R axis
specification is triggered by fertilization
• Primary embryonic induction.
• Hans Spemann and Hilde Mangold- The Organizer
Axis Specification in Xenopus: Molecular Mechanism• Dorsal Signal: b-catenin, Nodal, and Vg1.• Bone Morphogenic Proteins (BMPs)– noggin– chordin– follistatin
Regional Neural Induction in Xenopus• Head inducer: Wnt
inhibitors– Cerberus– Frzb, Dickkopf– Insulin-like Growth
factors• Trunk patterning:
– Wnt and Retinoic Acid
Frogs are left handed!• Xenopus Nodal related
protein (Xnr-1) determines left-right axis
• Xnr-1 is expressed on Left side.
• Pitx2 is activated by Xnr-1 and also persists on left side. Injection of Pitx2 on right side alters gut coiling and heart placement.
Early Vertebrate Development: Danio rerio
Danio Gastrulation
Epiboly and beginning formation of notocord
Axis Formation: Danio• D-V axis: BMP/Wnt inhibitors regulated by b-catenin and
Nodal-like proteins.• Fish Nieuwkoop center = Organizer.
Danio A-V axis formation
Left-Right Axis formation in Danio
Early Vertebrate Developement
Early Vertebrate Developement
Early Vertebrate Developement
Early Vertebrate Developement
Early Vertebrate Developement
Early Vertebrate Developement
Early Vertebrate Developement
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Early Vertebrate Developement
Early Vertebrate Developement
Early Vertebrate Developement
Early Vertebrate Developement