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. Xenopus Gastrulation: Involution Vegetal Rotation: Movement of Pharyngeal endoderm above involuting mesoderm. Involuting Marginal Zone (IMZ)

9. Xenopus: Gastrulation

10. Xenopus Gastrulation: 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:  -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! 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.

15. Early Vertebrate Development: Danio rerio

16. Danio Gastrulation

17. Epiboly and beginning formation of notocord

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

19. Danio A-V axis formation

20. Left-Right Axis formation in Danio

21. Early Vertebrate Developement