title: Chromatin tethering effects of hNopp140 are involved in the spatial organization of nucleolus and the rRNA gene transcription.
abstract: The short arms of five human acrocentric chromosomes contain ribosomal gene (rDNA) clusters where numerous mini-nucleoli arise at the exit of mitosis. These small nucleoli tend to coalesce into one or a few large nucleoli during interphase by unknown mechanisms. Here, we demonstrate that the N- and C-terminal domains of a nucleolar protein, hNopp140, bound respectively to alpha-satellite arrays and rDNA clusters of acrocentric chromosomes for nucleolar formation. The central acidic-and-basic repeated domain of hNopp140, possessing a weak self-self interacting ability, was indispensable for hNopp140 to build up a nucleolar round-shaped structure. The N- or the C-terminally truncated hNopp140 caused nucleolar segregation and was able to alter locations of the rDNA transcription, as mediated by detaching the rDNA repeats from the acrocentric alpha-satellite arrays. Interestingly, an hNopp140 mutant, made by joining the N- and C-terminal domains but excluding the entire central repeated region, induced nucleolar disruption and global chromatin condensation. Furthermore, RNAi knockdown of hNopp140 resulted in dispersion of the rDNA and acrocentric alpha-satellite sequences away from nucleolus that was accompanied by rDNA transcriptional silence. Our findings indicate that hNopp140, a scaffold protein, is involved in the nucleolar assembly, fusion, and maintenance.
authors.affiliation: School of Life Science, Institute of Microbiology and Immunology, National Yang-Ming University, 155 Li-Nong Street Sec. 2, Taipei, 112, Taiwan.
authors.forename: Yi-Tzang
authors.initials: YT
authors.lastname: Tsai
authors.forename: Chen-I
authors.initials: CI
authors.lastname: Lin
authors.forename: Hung-Kai
authors.initials: HK
authors.lastname: Chen
authors.forename: Kuo-Ming
authors.initials: KM
authors.lastname: Lee
authors.forename: Chia-Yi
authors.initials: CY
authors.lastname: Hsu
authors.forename: Shun-Jen
authors.initials: SJ
authors.lastname: Yang
authors.forename: Ning-Hsing
authors.initials: NH
authors.lastname: Yeh
mesh_terms: D002466:Cell Nucleolus / Q000737:chemistry / Q000378:metabolism*; D004275:DNA, Ribosomal / Q000235:genetics / Q000378:metabolism; D004276:DNA, Satellite / Q000378:metabolism; D020868:Gene Silencing; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D004275:DNA, Ribosomal; D004276:DNA, Satellite; C075564:NOLC1 protein, human; D009687:Nuclear Proteins; D010750:Phosphoproteins; D012335:RNA, Ribosomal