17 hours in the life of a zebrafish embryo Karlstrom and Kane, 1996

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

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

Somitogenesis 3-somite 6-somite 18-somite 26-somite 22 hr Kimmel et al., 1995

Zebrafish development Karlstrom and Kane, 1996

Early development ?

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

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

Gastrulation simplified

Cell movements during gastrulation involution Convergence- extension epiboly

Mesoderm & endoderm inside Involution Mesoderm & endoderm inside Ectoderm outside

Epiboly

Convergence-Extension

Convergence-extension

Convergence-extension

Convergence-Extension Marlow et al., 1998

Dorsal-Ventral Side view ventral dorsal top view

Fate maps reflect movement

Dorsal-ventral patterning Shield (Organizer)

The Organizer Shield (Organizer)

Repeating the Spemann organizer experiment

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

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

Summary

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

Neural Tube closure

Forming tubes Navis and Bagnat, 2015

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. 395:181-5. 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. 322:1065-9. Kimmel CB, Ballard WW, Kimmel SR, Ullmann B, Schilling TF. (1995). Stages of embryonic development of the zebrafish. Dev Dyn. 203:253-310. 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. 203:382-99. Navis A, Bagnat M 2015 Developing pressures: fluid forces driving morphogenesis. Current Opinion in Genetics & Development 2015, 32:24–30