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

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Presentation transcript:

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

17 hours in the life of a zebrafish embryo

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

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

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

Zebrafish development

Early development ?

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

Gastrulation simplified

Involution Mesoderm & endoderm inside Ectoderm outside

Dorsal-Ventral Side view top view dorsal ventral

Involuting cell movements during gastrulation

Convergence-Extension convergence extension

Convergence-Extension

Convergence-extension

Cell fates Dorsal view Cross section dorsal

Convergence-extension

Slow dorsal migration ConvergenceExtension Convergence-extension cell movements

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

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

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

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

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”

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

Animal viewVegetal view dorsal

Early Development Movies Slow-moving nucleus Fast moving nucleus

Early Development Movies dorsal

Early Development Movies

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

Signaling from the YSL

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

Normally ~1550 cells internalize; in MZoep ~60 internalize

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

Dorsal-ventral patterning Shield (Organizer)

Bozozok

The Organizer Shield (Organizer)

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)

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

Bmp regulates cell movement High Bmp Low Bmp

Summary