title: Dynamic redistribution of vasa homolog and exclusion of somatic cell determinants during germ cell specification in Ciona intestinalis.
abstract: Ascidian embryos sequester a specific cytoplasm, called the postplasm, at the posterior pole, where many maternal RNAs and proteins accumulate. Although the postplasm is thought to act as the germ plasm, it is also highly enriched in several factors essential for somatic cell development, and how the postplasm components regulate both germ and somatic cell differentiation remains elusive. Using a vasa homolog, CiVH, and other postplasmic components as markers, we found that the postplasm-containing blastomeres, the B7.6 cells, undergo an asymmetric cell division during gastrulation to produce two distinct daughter cells: B8.11 and B8.12. Most of the postplasmic components segregate only into the B8.11 cells, which never coalesce into the gonad. By contrast, the maternal CiVH RNA and protein are specifically distributed into the B8.12 cells, which divide further and are incorporated into the gonad in juveniles. In the B8.12 cells, CiVH production is upregulated from the maternal RNA source, resulting in the formation of perinuclear CiVH granules, which may be the nuage, a hallmark of germ cells in many animal species. We propose that the redistribution of specific maternal molecules into the B8.12 cells is essential for germ-cell specification in ascidians.
authors.affiliation: Laboratory for Germline Development, RIKEN Center for Developmental Biology, Kobe, Hyogo 650-0047, Japan. shirae@cdb.riken.jp
authors.forename: Maki
authors.initials: M
authors.lastname: Shirae-Kurabayashi
authors.forename: Takahito
authors.initials: T
authors.lastname: Nishikata
authors.forename: Katsumi
authors.initials: K
authors.lastname: Takamura
authors.forename: Kimio J
authors.initials: KJ
authors.lastname: Tanaka
authors.forename: Chiaki
authors.initials: C
authors.lastname: Nakamoto
authors.forename: Akira
authors.initials: A
authors.lastname: Nakamura
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D019070:Cell Lineage; D002938:Ciona intestinalis / Q000166:cytology* / Q000196:embryology* / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000033:anatomy & histology / Q000166:cytology; D018507:Gene Expression Regulation, Developmental; D005854:Germ Cells / Q000166:cytology / Q000502:physiology; D017403:In Situ Hybridization; D020365:RNA Helicases / Q000235:genetics / Q000378:metabolism*; D023121:RNA, Messenger, Stored / Q000378:metabolism
chemical_list: D015415:Biomarkers; D023121:RNA, Messenger, Stored; D020365:RNA Helicases