Because cleavage is impeded in the vegetal pole, there is a very uneven distribution and size of cells, being more numerous and smaller at the animal pole of the zygote.
12.
However, in cnidarians the depression forms at the end further from the yolk ( at the animal pole ), while in bilaterians it forms at the other end ( vegetal pole ).
13.
In the early blastula stage of the embryo, Ectodermin mRNA and protein forms a gradient that goes from the animal pole ( highest concentration ) down to the marginal zone ( lowest concentration ) to prevent TGF? and nodal signals that induce mesoderm originating from the vegetal pole.
14.
For instance, in "'Figure 1 "', Nile Blue staining of a 32-cell blastula at the dorsal side of the animal pole yields a blue-stained brain and ( depending on the size of the agar chip ) may also stain the anterior portion of the notochord.
