title: The Dr-nanos gene is essential for germ cell specification in the planarian Dugesia ryukyuensis.
abstract: Homologs of nanos are required for the formation and maintenance of germline stem cell (GSC) systems and for gametogenesis in many metazoans. Planarians can change their reproductive mode seasonally, alternating between asexual and sexual reproduction; they develop and maintain their somatic stem cells (SSCs) and GCSs from pluripotent stem cells known as neoblasts. We isolated a nanos homolog, Dr-nanos, from the expressed sequence tags (ESTs) of the sexualized form of Dugesia ryukyuensis. We examined the expression of Dr-nanos in asexual and sexualized planarians by in situ hybridization and analyzed its function using RNA interference (RNAi) together with a planarian sexualization assay. A nanos homolog, Dr-nanos, was identified in the planarian D. ryukyuensis. Dr-nanos expression was observed in the ovarian primordial cells of the asexual worms. This expression increased in proportion to sexualization and was localized in the early germline cells of the ovaries and testes. In X-ray-irradiated worms, the expression of Dr-nanos decreased to a large extent, indicating that Dr-nanos is expressed in some subpopulations of stem cells, especially in GSCs. During the sexualization process, worms in which Dr-nanos was knocked down by RNAi exhibited decreased numbers of oogonia in the ovaries and failed to develop testes, whereas the somatic sexual organs were not affected. We conclude that Dr-nanos is essential for the development of germ cells in the ovaries and testes and may have a function in the early stages of germ cell specification, but not in the development of somatic sexual organs.
authors.affiliation: Department of Biological Sciences and Informatics, Keio University, Hiyoshi, Kouhoku-ku, Yokohama, Japan.
authors.forename: Haruka
authors.initials: H
authors.lastname: Nakagawa
authors.forename: Hirotsugu
authors.initials: H
authors.lastname: Ishizu
authors.forename: Ayako
authors.initials: A
authors.lastname: Chinone
authors.forename: Kazuya
authors.initials: K
authors.lastname: Kobayashi
authors.forename: Midori
authors.initials: M
authors.lastname: Matsumoto
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D020224:Expressed Sequence Tags; D005260:Female; D005854:Germ Cells / Q000166:cytology* / Q000502:physiology*; D015801:Helminth Proteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D008297:Male; D008969:Molecular Sequence Data; D010053:Ovary / Q000166:cytology; D010932:Planarians / Q000166:cytology / Q000502:physiology*; D034741:RNA, Small Interfering / Q000235:genetics; D012038:Regeneration / Q000502:physiology; D012100:Reproduction, Asexual; D017386:Sequence Homology, Amino Acid; D013234:Stem Cells / Q000166:cytology / Q000502:physiology*; D013737:Testis / Q000166:cytology
chemical_list: D015801:Helminth Proteins; D034741:RNA, Small Interfering