Review 5869 Mechanisms of germ cell specification across the metazoans: epigenesis and preformation Cassandra G. Extavour* and Michael Akam Laboratory for Development and Evolution, University Museum of Zoology, Department of Zoology, Downing Street, Cambridge CB2 3EJ, UK *Author for correspondence (e-mail:
[email protected]) Development 130, 5869-5884 © 2003 The Company of Biologists Ltd doi:10.1242/dev.00804 Summary Germ cells play a unique role in gamete production, on 28 metazoan phyla, which indicate that although heredity and evolution. Therefore, to understand the preformation is seen in most model organisms, it is actually mechanisms that specify germ cells is a central challenge in the less prevalent mode of germ cell specification, and that developmental and evolutionary biology. Data from model epigenetic germ cell specification may be ancestral to the organisms show that germ cells can be specified either by Metazoa. maternally inherited determinants (preformation) or by inductive signals (epigenesis). Here we review existing data Supplemental data available online Introduction gonia become oocytes and spermatocytes, maturing finally into Germ cell segregation is an important problem in ova and spermatozoa, respectively. Many organisms generate developmental biology, as it addresses how the fundamental their gonia from cells capable of almost indefinite rounds of distinctions between germ cells and somatic cells are initiated asymmetric, self-renewing mitotic divisions; these cells are and maintained throughout development. The timing and called germ line stem cells. The first cells that will give rise mechanism of this segregation are also important for our exclusively to germ cells by clonal mitotic divisions are called understanding of evolution, for these influence the selective primordial germ cells (PGCs).