Chromatin tethering effects of hNopp140 are involved in the spatial organization of nucleolus and the rRNA gene transcription.
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.
Tsai
Yi-Tzang
YT
School of Life Science, Institute of Microbiology and Immunology, National Yang-Ming University, 155 Li-Nong Street Sec. 2, Taipei, 112, Taiwan.
Lin
Chen-I
CI
Chen
Hung-Kai
HK
Lee
Kuo-Ming
KM
Hsu
Chia-Yi
CY
Yang
Shun-Jen
SJ
Yeh
Ning-Hsing
NH
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
D004275:DNA, Ribosomal; D004276:DNA, Satellite; C075564:NOLC1 protein, human; D009687:Nuclear Proteins; D010750:Phosphoproteins; D012335:RNA, Ribosomal