title: Requirement of the protein B23 for nucleolar disassembly induced by the FRGY2a family proteins.
abstract: In Xenopus somatic cell nuclear cloning, the nucleoli of donor nuclei rapidly and almost completely disappear in egg cytoplasm. We previously showed that the germ cell-specific proteins FRGY2a and FRGY2b were responsible for this unusually drastic nucleolar disassembly. The nucleolar disassembly occurs without inhibition of pre-rRNA transcription, a well known trigger for nucleolar segregation, and the mechanism for the nucleolar disassembly by FRGY2a and FRGY2b remains largely unknown. In this study, we searched for FRGY2a-interacting proteins and investigated the functional consequences of their interactions through a series of experiments. We showed that during the nucleolar disassembly, FRGY2a localized to the nucleoli of isolated nuclei and was capable of disassembling purified nucleoli, suggesting a direct interaction between FRGY2a and nucleolar components. Using a His tag pulldown approach, we identified the abundant and multifunctional nucleolar protein B23 as a potential target of FRGY2a and its related human protein YB1. A specific interaction between FRGY2a/YB1 and B23 was confirmed by co-immunoprecipitation. Finally, B23 knockdown using short interfering RNA and a subsequent add-back experiment confirmed that B23 was necessary for nucleolar disassembly by YB1. We propose that FRGY2a and YB1 disassemble nucleoli by sequestering B23, which is associated with pre-ribosomes and other structurally important nucleolar components.
authors.affiliation: Stem Cell Institute, Division of Hematology, Oncology and Transplantation, Department of Medicine, University of Minnesota, Minneapolis, Minnesota 55455, USA.
authors.forename: Koichi
authors.initials: K
authors.lastname: Gonda
authors.forename: Justin
authors.initials: J
authors.lastname: Wudel
authors.forename: Dominic
authors.initials: D
authors.lastname: Nelson
authors.forename: Nobuko
authors.initials: N
authors.lastname: Katoku-Kikyo
authors.forename: Peter
authors.initials: P
authors.lastname: Reed
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Tamada
authors.forename: Nobuaki
authors.initials: N
authors.lastname: Kikyo
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D002466:Cell Nucleolus / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000378:metabolism; D006367:HeLa Cells; D006639:Histidine / Q000737:chemistry; D006801:Humans; D047468:Immunoprecipitation; D013058:Mass Spectrometry; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D009687:Nuclear Proteins / Q000378:metabolism / Q000502:physiology*; D000090243:Nucleophosmin; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D034741:RNA, Small Interfering / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D011994:Recombinant Proteins / Q000737:chemistry; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors / Q000378:metabolism / Q000502:physiology*; D014162:Transfection; D014981:Xenopus; D029867:Xenopus Proteins / Q000378:metabolism / Q000502:physiology*
chemical_list: D018076:DNA, Complementary; D009687:Nuclear Proteins; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins; D014157:Transcription Factors; D029867:Xenopus Proteins; C075593:YBX2 protein, Xenopus; D000090243:Nucleophosmin; D006639:Histidine