1. Gastrulation It is not birth, marriage or death, but gastrulation, which is truly the most important event in your life Lewis Wolpert

2. 17 hours in the life of a zebrafish embryo

3. Blastula Stages 1- cell2-cell 4-cell 8-cell 32-cell 512-cell 1000-cell Transcription begins sphere dome 30% epiboly 4 2/3 hrs

4. Gastrula Stages 50% germ ring shield 75%90% bud 10 hr

5. Somitogenesis 3-somite 6-somite18-somite 26-somite 22 hr

6. Zebrafish development

7. Early development ?

8. Three germ layers Side view top view Skin & nervous system Muscle & cardiovascular Gut and liver Animal pole Vegetal pole

9. Gastrulation simplified

10. Involution Mesoderm & endoderm inside Ectoderm outside

11. Dorsal-Ventral Side view top view dorsal ventral

12. Involuting cell movements during gastrulation

13. Convergence-Extension convergence extension

14. Convergence-Extension

15. Convergence-extension

16. Cell fates Dorsal view Cross section dorsal

17. Convergence-extension

19. Slow dorsal migration ConvergenceExtension Convergence-extension cell movements

20. Slow dorsal migration Fast dorsal migration ConvergenceExtension Convergence-extension cell movements

21. Slow dorsal migration Fast dorsal migration ConvergenceExtension Packing, inhibition of protrusions Convergence-extension cell movements

22. Slow dorsal migration Fast dorsal migration Packing, inhibition of protrusions Intercalation ConvergenceExtension Convergence-extension cell movements

24. Summary Formation of germ layers Convergence- extension Formation of tissue boundaries Cleavage

25. Early Development movies Histone 2BGFP Made RNA Injected embryos at the 1-cell stage Imaged with Digital Scanned Laser Light Sheet Fluorescence Microscopy (capture whole embryo image every 60-90s) Produced a “digital embryo”

26. 512-cell Divisions symmetric prior to 512-cell Divisions asymmetric after 512-cell Radial waves just after 512-cell Early Development Movies

28. Animal viewVegetal view dorsal

30. Early Development Movies Slow-moving nucleus Fast moving nucleus

33. Early Development Movies dorsal

35. Early Development Movies

37. Two major Questions How are the germ layers established? What determines polarity?

38. Signaling from the YSL

39. Nodal mutant wild-type sqt;cyc -/- No endoderm No head & trunk mesoderm

40. Normally ~1550 cells internalize; in MZoep ~60 internalize

41. Germ layer patterning YSL signal Sqt and Cyc Endoderm Head and Trunk Mesoderm Tail mesoderm

42. Dorsal-ventral patterning Shield (Organizer)

43. Bozozok

44. The Organizer Shield (Organizer)

45. Bmp promotes ventral fates Organizer signals are BMP binding factors: Noggin, Chordin Bmp signals promote ventral fates (skin, ventral mesoderm) and oppose dorsal fates (neural, dorsal mesoderm)

46. Mutants in the dorsal-ventral pathway Snailhouse (snh) = bmp7 mutant Chordino (din) = chordin mutant

47. Bmp regulates cell movement High Bmp Low Bmp

48. Summary