Developmental Biology Chapter 10: Sea Urchins: Deuterostome Invertebrate

What type of cleavage do sea urchins undergo?

Radial holoblastic cleavage

Cleavage 1 & 2 results in an

equal division of the cells with respect to the animals and vegetal pole

Cleavage 3

separates the animal and vegetal poles.

The 4th cleavage yields 8 cells of equal size called ____________ on the animal half of the embryo.

mesomeres

On the vegetal pole, 4 larger cells (____________) and 4 smaller cells (_______________) are produced

macromeres, mesosmeres

a hollow cavity that forms in the blastula

Blastocoel

True or False: At the blastula stage, cells are more closely connected through tight junctions which allows them to form one-cell layer epithelial sheet around the blastocoel

True

The blastocoel will then expand due to an

Influx of water

When the blastula releases enzymes from the animal pole that will allow it to escape from the fertilization envelope it is called

hatched blastula

The fate of the different cell layers in sea urchin embryos are determined in two steps:

1.Autonomous specification

2.Conditional specification

inherited maternal determinants deposited in the vegetal pole instruct the large micromeres to become the skeleton. They develop on their own

Autonomous specification

the autonomously specified large micromeres produce paracrine and juxtacrine factors that instruct the cells above them to become endoderm

Conditional specification

drives specification of the endoderm and mesoderm from the vegetally derived micromeres

Disheveled and B-catenin