title: The diversity of nanos expression in echinoderm embryos supports different mechanisms in germ cell specification.
abstract: Specification of the germ cell lineage is required for sexual reproduction in all animals. However, the timing and mechanisms of germ cell specification is remarkably diverse in animal development. Echinoderms, such as sea urchins and sea stars, are excellent model systems to study the molecular and cellular mechanisms that contribute to germ cell specification. In several echinoderm embryos tested, the germ cell factor Vasa accumulates broadly during early development and is restricted after gastrulation to cells that contribute to the germ cell lineage. In the sea urchin, however, the germ cell factor Vasa is restricted to a specific lineage by the 32-cell stage. We therefore hypothesized that the germ cell specification program in the sea urchin/Euechinoid lineage has evolved to an earlier developmental time point. To test this hypothesis we determined the expression pattern of a second germ cell factor, Nanos, in four out of five extant echinoderm clades. Here we find that Nanos mRNA does not accumulate until the blastula stage or later during the development of all other echinoderm embryos except those that belong to the Echinoid lineage. Instead, Nanos is expressed in a restricted domain at the 32-128 cell stage in Echinoid embryos. Our results support the model that the germ cell specification program underwent a heterochronic shift in the Echinoid lineage. A comparison of Echinoid and non-Echinoid germ cell specification mechanisms will contribute to our understanding of how these mechanisms have changed during animal evolution.
authors.affiliation: Department of Molecular Biology, Cell Biology and Biochemistry, Brown University, 185 Meeting Street, Providence RI 02912.
authors.forename: Tara
authors.initials: T
authors.lastname: Fresques
authors.affiliation: Department of Molecular Biology, Cell Biology and Biochemistry, Brown University, 185 Meeting Street, Providence RI 02912.
authors.forename: Steven Zachary
authors.initials: SZ
authors.lastname: Swartz
authors.affiliation: Department of Molecular Biology, Cell Biology and Biochemistry, Brown University, 185 Meeting Street, Providence RI 02912.|Department of Molecular and Cellular Biology, College of Biological Sciences, University of California, One Shields Avenue, Davis, CA 95616.
authors.forename: Celina
authors.initials: C
authors.lastname: Juliano
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba 305-8572, Japan.
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Morino
authors.affiliation: Misaki Marine Biological Station, Graduate School of Science, University of Tokyo, Koajiro 1024, Misaki, Miura 238-0225, Japan.
authors.forename: Mani
authors.initials: M
authors.lastname: Kikuchi
authors.affiliation: Misaki Marine Biological Station, Graduate School of Science, University of Tokyo, Koajiro 1024, Misaki, Miura 238-0225, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Akasaka
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba 305-8572, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Wada
authors.affiliation: Department of Molecular Biology, Cell Biology and Biochemistry, Brown University, 185 Meeting Street, Providence RI 02912.
authors.forename: Mamiko
authors.initials: M
authors.lastname: Yajima
authors.affiliation: Department of Molecular Biology, Cell Biology and Biochemistry, Brown University, 185 Meeting Street, Providence RI 02912.
authors.forename: Gary M
authors.initials: GM
authors.lastname: Wessel
mesh_terms: D000818:Animals; D053487:DEAD-box RNA Helicases / Q000235:genetics / Q000378:metabolism; D004447:Echinodermata / Q000145:classification / Q000196:embryology* / Q000235:genetics / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000378:metabolism; D015870:Gene Expression; D005854:Germ Cells; D012333:RNA, Messenger / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D053487:DEAD-box RNA Helicases