Zebrafish development Monday, May 26

Zebrafish An ideal subject for imaging and manipulation. Very small species of minnow Native to the Ganges region of India Named for distinctive stripes Zebrafish have been popularized as a model for studying vertebrate development: Cell biology and development Organ system development Genetic studies Toxicology Environmental biology

Stages of Zebrafish Development Key: =Injection stage =Imaging stage

Fertilization

Devo gone wrong!

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

Cleavage in Zebrafish What kind of cleavage occurs in fish?

Cleavage in Zebrafish At the time of the mid-blastula transition three cell populations form: – yolk syncytial layer (YSL) – enveloping layer (EVL) – deep cells What is the importance of each?

GASTRULATION is a complex series of cell movements that: --rearranges cells, giving them new neighbors --results in the formation of 3 GERM LAYERS that will form the subsequent embryo: ectoderm, endoderm and mesoderm --forms the main body axes of the embryo (they were specified earlier but not formed)

Animal and vegetal poles A blastula embryo is divided into two hemispheres: the animal pole and the vegetal pole. The animal pole consists of small cells that divide rapidly, in contrast with the vegetal pole below it. – The animal pole draws its name from its liveliness relative to the slowly developing vegetal pole

Gastrulation in Fish How does gastrulation begin?

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

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

ECTODERM-- --skin, nervous system, neural crest MESODERM-- --muscle, bones, blood and vessels, kidney, gonads, connective tissue ENDODERM-- --gut, liver, lungs, pancreas

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

Axis Formation in Fish How has it been demonstrated that the embryonic shield is critical to dorsal-ventral axis formation? What structures form from it?

Axis Formation in Fish How does notocord induce neural structures from overlying ectoderm?

Axis Formation in Fish Where is the Nieuwkoop center and how does it function? What determines the anterior-posterior axis?

Neurulation

Neural tube (hollow): formed by subsequent closure of neural plate in fish it is a rod first, then becomes hollow

Fish 1. neural plate forms on dorsal half of epiblast 2. cells on both sides of median hinge point grow together 3. rounded rod: neural keel

Organogenesis