From one fertilized egg, need to undergo
- Reproduction - (Evolution) Gastrulation
Highly ordered cell and tissue movements occur whereby cells
of the blastula are rearranged.
Results in the formation of Germ Layers. Most higher phyla – 3 axes:Anterior/Posterior,
Dorsal/Ventral and Left/Right
- often bilateral
- are triploblastic
(3 germ layers)
The evolution of mesoderm
had important consequences
on the diversity of metazoans.
Sea urchins are not bilateral,
but are still triploblastic Meso
In the sea urchin blastula
(as in others), cells are Macro
Micromeres are able
induce ectodermal cells
(mesomeres) to acquire
Sea Urchin development
Pgs 217-232 Micromeres can induce a secondary
axis in sea urchin embryos if added
to anterior regions.
(competence and induction) -catenin helps specify the vegetal cells of the urchin embryo;
(-catenin is stained by a fluorescently labeled antibody)
- catenin distribution Normal sea urchin development,
following the fate of the cellular layers
and cell movements of the blastula. Also, convergent extension convergent
extension Sea Urchin Gastrulation
Ingression of primary mesenchymal cells Sea Urchin gastrulation
At about 1000 cells vegetal plate (VP) forms.
(includes original micromeres - red)
As gastrulation begins, some VP cells ingress into blastocoel
and form 1º mesenchyme-blue.
(subsequently, remaining VP cells invaginate forming an