Abstract
ABSTRACTNucleoli have attracted interest for their role as cellular stress sensors and as potential targets for cancer treatment. The effect of DNA double-strand breaks (DSBs) in nucleoli on rRNA transcription and nucleolar organisation appears to depend on the agent used to introduce DSBs, DSB frequency and the presence (or not) of DSBs outside the nucleoli. To address the controversy, we targeted nucleoli with carbon ions at the ion microbeam SNAKE. Localized ion irradiation with 1–100 carbon ions per point (about 0.3–30 Gy per nucleus) did not lead to overall reduced ribonucleotide incorporation in the targeted nucleolus or other nucleoli of the same cell. However, both 5-ethynyluridine incorporation and Parp1 protein levels were locally decreased at the damaged nucleolar chromatin regions marked by γH2AX, suggesting localized inhibition of rRNA transcription. This locally restricted transcriptional inhibition was not accompanied by nucleolar segregation, a structural reorganisation observed after inhibition of rRNA transcription by treatment with actinomycin D or UV irradiation. The presented data indicate that even multiple complex DSBs do not lead to a pan-nucleolar response if they affect only a subnucleolar region.
Highlights
Nucleoli are the largest organelles within the cell nucleus
Nucleoli harbour several hundred copies of 13 kb ribosomal DNA coding sequences, each separated by intergenic sequences (IGS) of about 30 kb length
HeLa poly [ADP-ribose] polymerase 1 (Parp1)–CB-tagRFP cells expressing an RFP-tagged chromobody (CB) that binds Parp1 (Buchfellner et al, 2016) demonstrate nucleolar accumulation of endogenous Parp1 protein (Fig. 1), a fact that we exploited for targeted irradiation of nucleoli
Summary
Nucleoli are the largest organelles within the cell nucleus. In addition to their function in transcription and processing of ribosomal RNA (rRNA), they have attracted interest for their role as cellular stress sensors and as potential therapeutic targets for cancer treatment (Boulon et al, 2010; Hein et al, 2013; Lindström et al, 2018). Received 21 March 2019; Accepted 29 August 2019 with the architectural transcription factor UBF, whereas IGS regions exhibit a nucleosomal structure (O’Sullivan et al, 2002; Zentner et al, 2011; Herdman et al, 2017). Cells expressing fluorescencetagged histones show fibres of intranucleolar condensed chromatin (ICC) in close contact with fibrillary centres (FCs) (Tchelidze et al, 2017). The ICC fibres seem to connect with perinucleolar condensed chromatin (PCC), which surrounds the nucleoli
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
