Formation of blastula

Gastrulation

Early gastrulaectoderm: blue; dorsal lip of blastopore: greenendoderm: yellow; yolk: orange

Mid-gastrulaBlue: ectoderm; Green: chordomesodermRed: mesoderm (ventral lip); Yellow: endoderm

Late gastrula (yolk plug stage)Green: notochordYellow: endoderm lining the archenteron

Formation of neural plate and early neurulation

Neural tube stage and late neurula

3-4 mm frog embryoFormation of brain vescicles:

prosencephalonmesencephalonrhombencephalon

In situ hybridization

Steps in the activationof a receptor tyrosinekinase:

Neural Induction

Mechanical factors which may contribute toNeurulation:

Cadherins and cell adhesion

Example of Cell-CellRecognition viaCadherins: