title: CiYB1 is a major component of storage mRNPs in ascidian oocytes: implications in translational regulation of localized mRNAs.
abstract: In ascidian eggs, the existence of several localized maternal cytoplasmic determinants has been proposed and the importance of localized mRNAs for tissue differentiation has been demonstrated. We previously identified the ascidian Y-box proteins (CiYB1, 2 and 3), homologues of which are known to be involved in the storage of maternal mRNA in oocytes of other organisms. In this study, we found that CiYB1 protein is abundant in the gonad, egg, and embryo. Purification of messenger ribonucleoprotein (mRNP) particles from the gonad revealed that CiYB1 was one of their major components. A significant change in the distribution of CiYB1 protein from stored mRNP particles in the gonad to the ribosome fraction in eggs and embryos was observed. This change correlates most likely with the shift of stored maternal mRNAs to polyribosomes. Moreover, we found that CiYB1 colocalized with Cipem and Ci-macho1 mRNAs, which are localized at the posterior end of the embryo at the cleavage stage. Cipem and Ci-macho1 mRNAs were co-immunoprecipitated with CiYB1 in the oocyte and embryo lysates. The formation of a complex between Cipem mRNA and CiYB1 protein resulted in translational repression in the in vitro translation system. Our results indicate that associating with CiYB1 protein contributes to the translational control of the localized mRNA in eggs and embryos.
authors.affiliation: Laboratory of Cellular Biochemistry, RIKEN (The Institute of Physical and Chemical Research), Wako, Saitama 351-0198, Japan.
authors.forename: Kimio J
authors.initials: KJ
authors.lastname: Tanaka
authors.forename: Ken
authors.initials: K
authors.lastname: Matsumoto
authors.forename: Masafumi
authors.initials: M
authors.lastname: Tsujimoto
authors.forename: Takahito
authors.initials: T
authors.lastname: Nishikata
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002938:Ciona intestinalis / Q000196:embryology / Q000235:genetics* / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004527:Egg Proteins / Q000235:genetics / Q000378:metabolism; D004625:Embryo, Nonmammalian; D005260:Female; D005786:Gene Expression Regulation; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D009865:Oocytes / Q000502:physiology*; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D012261:Ribonucleoproteins / Q000235:genetics / Q000378:metabolism*; D015053:Zygote / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D004527:Egg Proteins; D006360:Heat-Shock Proteins; D047908:Intracellular Signaling Peptides and Proteins; D046911:Macromolecular Substances; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D012261:Ribonucleoproteins; C117519:Y-box protein, Ciona intestinalis; C420970:macho-1 protein, Halocynthia roretzi; C026452:messenger ribonucleoprotein