Biochemistry 3381A Study Guide - Quiz Guide: Blastocoel, Blastula, Fate Mapping
27 May 2020
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After the seventh cleavage the blastula stage is reached. The embryo now consists of 120 cells which surround a central cavity = blastocoel. In the blastula stage, the cells form a seamless epithelial sheet completely encircling the blastocoel. Each cell is in contact with the blastocoel and cells are connected via tight junctions. The blastula remains one cell layer thick during the next divisions (until 9th or 10th) Now the cells become ciliated, the vegetal pole thickens and the cells on the animal pole secrete an enzyme that digests the fertilization envelope: hatching to a free-swimming blastula. Determination of sea urchin blastomeres a fate map of 60 cell stage: the first cells that are specified are the large micromeres: Large micromeres inherit maternal factors (disheveled, -catenin) that were deposited on the vegetal pole of the egg. The large micromers are able to induce a normal larval development of the animal of the embryo.
