1 17 hours in the life of a zebrafish embryoKarlstrom and Kane, 1996

2 Blastula Stages 2-cell 4-cell 8-cell 32-cell 512-cell 1000-cell spheredome 30% epiboly 4 2/3 hrs Transcription begins Kimmel et al., 1995

3 Gastrula Stages shield 50% germ ring 75% 90% bud 10 hrKimmel et al., 1995

4 Somitogenesis 3-somite 6-somite 18-somite 26-somite 22 hrKimmel et al., 1995

5 Zebrafish developmentKarlstrom and Kane, 1996

6 Early development ?

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

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

9 Gastrulation simplified

10 Cell movements during gastrulationinvolution Convergence- extension epiboly

11 Mesoderm & endoderm insideInvolution Mesoderm & endoderm inside Ectoderm outside

12 Epiboly

13 Convergence-Extension

14 Convergence-extension

15 Convergence-extension

16 Convergence-ExtensionMarlow et al., 1998

17 Dorsal-Ventral Side view ventral dorsal top view

18 Fate maps reflect movement

19 Dorsal-ventral patterningShield (Organizer)

20 The Organizer Shield (Organizer)

21 Repeating the Spemann organizer experiment

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

23 Mutants in the dorsal-ventral pathwaySnailhouse (snh) = bmp7 mutant Chordino (din) = chordin mutant

24 Summary

25 Questions How are gradients established and interpreted? How do cells form distinct compartments? How do groups of cells arrange into tissues and organs?

26 Neural Tube closure

27 Forming tubes Navis and Bagnat, 2015

28 References Feldman B, Gates MA, Egan ES, Dougan ST, Rennebeck G, Sirotkin HI, Schier AF, Talbot WS. (1998). Zebrafish organizer development and germ-layer formation require nodal-related signals. Nature. 395: Karlstrom RO, Kane DA. (1996). A flipbook of zebrafish embryogenesis. Development. 123:461. Keller PJ, Schmidt AD, Wittbrodt J, Stelzer EH. (2008). Reconstruction of zebrafish early embryonic development by scanned light sheet microscopy. Science. 322: Kimmel CB, Ballard WW, Kimmel SR, Ullmann B, Schilling TF. (1995). Stages of embryonic development of the zebrafish. Dev Dyn. 203: Marlow F, Zwartkruis F, Malicki J, Neuhauss SC, Abbas L, Weaver M, Driever W, Solnica-Krezel L. (1998). Functional interactions of genes mediating convergent extension, knypek and trilobite, during the partitioning of the eye primordium in zebrafish. Dev Biol. 203: Navis A, Bagnat M 2015 Developing pressures: fluid forces driving morphogenesis. Current Opinion in Genetics & Development 2015, 32:24–30