Condensin Function in Mitotic Nucleolar Segregation is Regulated by rDNA Transcription

Abstract

ACKNOWLEDGEMENTSWe thank M. Nomura, T. Kobayashi, S. Roeder and S. Liebman for strains and plasmids; Micheal Lichten and A. Hinnebusch for critical reading of the manuscript; K. Bloom and A. Arnaoutov for time-lapse microscopy advice; R. Mehta and J. Panebianco for technical help. This research was supported by the Intramural Research Program of the NIH at the NICHD and at the Center for Cancer Research, NCI. NOTESupplemental information can be found at: http://www.landesbioscience.com/journals/cc/ supplement/wangCC5-19-sup.pdf. http://www.landesbioscience.com/journals/cc/ supplement/wangCC5-16-sup_2A.mov. http://www.landesbioscience.com/journals/cc/ supplement/wangCC5-16-sup_2B.mov. Report Condensin Function in Mitotic Nucleolar Segregation is Regulated by rDNA Transcription ABSTRACTChromosome condensation is established and maintained by the condensin complex. The mechanisms governing loading of condensin onto specific chromosomal sites remain unknown. To elucidate the molecular pathways that determine condensin binding to the nucleolar organizer, a key condensin binding site, we analyzed the properties of condensin-bound sites within the rDNA repeat in budding yeast and demonstrated that the bulk of mitotic condensin binding to rDNA is reduced or eliminated when Pol I transcription is elevated. Conversely, when Pol I transcription is repressed either by rapamycin treatment or by promoter shut-off, condensin binding to rDNA is increased. This novel potential role for constitutive and/or periodic repression of Pol I transcription in rDNA condensin loading is an important factor in determining the segregation proficiency of NOR-containing chromosomes.

In vivo modeling of polysumoylation uncovers targeting of Topoisomerase II to the nucleolus via optimal level of SUMO modification

“…The localization of Topoisomerase II to a subnucleolar compartment has been also described in the metazoan system: The C-terminal domain of mammalian Topoisomerase II beta localizes to a subnucleolar structure (Sakaguchi et al 2001). One of the nucleolus-specific functions of Top2p could be rDNA transcription by RNA polymerase I (Brill et al 1987), especially prominent in yeast where rDNA is constantly transcribed (Wang et al 2006). However, we may have uncovered a more general role of heavy sumoylation in nucleolar maintenance, by showing that the bulk of SUMO is concentrated in the nucleolus in the smt4Δ mutant.…”

“…The nucleolar organizer (or rDNA) is another prominent locus in the yeast genome that has a special Top2p requirement (Brill et al 1987;Christman et al 1988;Kim and Wang 1989), probably because of active transcription of rDNA throughout the cell cycle (Wang et al 2006). Therefore, we compared Top2p-5SUMO-GFP localization with that of the nucleolar protein Sik1-mRFP.…”

“…Ribosomal DNA (rDNA) quantification by quantitative real-time PCR (qPCR) was performed essentially as described previously (Wang et al 2006). Briefly, total yeast DNA was purified from test strains grown asynchronously to the same OD 600 =0.8, DNA concentrations in different samples were further equalized in accordance with spectrometric reading.…”

Transcriptional homogenization of rDNA repeats in the episome-based nucleolus induces genome-wide changes in the chromosomal distribution of condensin

“…Mitotic condensin enrichment in nucleolar chromatin apparently occurs without additional condensin synthesis, by its relocalization from non-rDNA sites . After cells exit mitosis, condensin is largely released from rDNA (Wang et al, 2006), suggesting existence of a molecular mechanism facilitating these dynamic changes in condensin localization. Transcriptional activity of RNA PolI is the process that has been implicated in this control (Wang et al, 2006).…”

Heterozygous De Novo UBTF Gain-of-Function Variant Is Associated with Neurodegeneration in Childhood

“…25 Impaired binding of condensin to untranscribed rDNA is associated with premature sister chromatids separation, before damage repair is completed. 26 Finally, UBF is an important regulator of chromatin structure at the rDNA locus; it was shown to outcompete linker Histone H1 resulting in decondensation of rDNA chromatin. 17 Changes in chromatin status at the rDNA locus, coupled with nucleolar alterations, have been previously reported in Huntington disease [MIM 143100] 16 and were regulated by UBF post-translational modification by acetylation at Lys-352 and methylation at Lys-232.…”