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Early Vertebrate Development

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.

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Early Vertebrate Development

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  1. Early Vertebrate Development • Axis Determination • Amphibian Early Development: Frog • Fish Early Development: Zebra Fish

  2. Heads or Tails? Axis specification • Common theme in early development • Conserved mechanisms • Divergent mechanisms

  3. Early Vertebrate Development: Xenopus

  4. Xenopus: Cleavage • Sperm entry point: Dorsal-Ventral (D-V) axis • Microtubule array • Cortical rotation.

  5. 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

  6. Mid-Blastula Transition • DNA demethylation • H3K4 methylated (trimethylation) transcription activation • Ex. Vegetal cells  endoderm. Produce paracrine factors that induce mesoderm specification of cells above.

  7. Xenopus: Gastrulation • Same goals as other organsims: get cells to appropriate locations! • Movements start in Gray Crescent, cells invaginate to form slit-like blastopore.

  8. XenopusGastrulation: Involution Vegetal Rotation: Movement of Pharyngeal endoderm above involuting mesoderm. InvolutingMarginal Zone (IMZ)

  9. Xenopus: Gastrulation

  10. XenopusGastrulation: Convergent extension

  11. 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

  12. Axis Specification in Xenopus: Molecular Mechanism • Dorsal Signal: b-catenin, Nodal, and Vg1. • Bone Morphogenic Proteins (BMPs) • noggin • chordin • follistatin

  13. Regional Neural Induction in Xenopus • Head inducer: Wnt inhibitors • Cerberus • Frzb, Dickkopf • Insulin-like Growth factors • Trunk patterning: • Wnt and Retinoic Acid

  14. Frogs are left handed! • XenopusNodal 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.

  15. Early Vertebrate Development: Daniorerio

  16. DanioGastrulation

  17. Epiboly and beginning formation of notocord

  18. Axis Formation: Danio • D-V axis: BMP/Wnt inhibitors regulated by b-catenin and Nodal-like proteins. • Fish Nieuwkoop center = Organizer.

  19. DanioA-V axis formation

  20. Left-Right Axis formation in Danio

  21. Early Vertebrate Developement

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