Molecular markers of oocyte and primordial germ cell development in the sea urchin

Beginning over 150 years ago, sea urchins have been an essential experimental tool for our understanding of fertilization and early development. Here we summarize our recent progress on the molecular mechanisms of oocyte development and fertilization in the sea urchin resulting from completing the sequence of the purple sea urchin genome. This genomic information has enabled us to predict gene sequences and then to test which genes are expressed in oocytes, how they function, and where the primordial germ cells originate in this animal. We have learned that oocytes express a unique set of genes that appear essential for their growth, for meiotic recombination and division, for storage of nutrition, and for fertilization. Sea urchin orthologs of the genes important in primordial germ cell development were also found localized to the oocyte, as well as to cells of the small micromere lineage. As a result, we believe that the small micromeres have the molecular characteristics of primordial germ cells in this organism.This cataloging of genes and their homologous functions allows us to ascribe echinoderm-specific functions that will broaden our understanding of fertilization and germ line development in animals.