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

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-cell 2-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-somite 18-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 insideEctoderm outside

Dorsal-Ventral

Side view

top view

dorsal

dorsal

ventral

ventral

Involuting cell movements during gastrulation

Convergence-Extension

convergence

extension

Convergence-Extension

Convergence-extension

Cell fates

Dorsal viewCross section

dorsal

dorsal

Convergence-extension

Convergence-extension

Slow dorsal migration

Convergence Extension

Convergence-extension cell movements

Slow dorsal migration

Fast dorsal migration

Convergence Extension

Convergence-extension cell movements

Slow dorsal migration

Fast dorsal migration

Convergence Extension

Packing, inhibition of protrusions

Convergence-extension cell movements

Slow dorsal migration

Fast dorsal migration

Packing, inhibition of protrusions

Intercalation

Convergence Extension

Convergence-extension cell movements

Convergence-extension cell movements

Summary

Formation ofgerm layers

Convergence-extension

Formation oftissue boundaries

Cleavage

Early Development movies

Histone 2B GFP

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

Early Development Movies

Animal view Vegetal view

dorsal dorsal

dorsaldorsal

dorsal

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 endodermNo 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