Trypanosoma brucei RAP1 maintains telomere and subtelomere integrity by suppressing TERRA and telomeric RNA:DNA hybrids. Issue 10 (16th March 2017)

• Record Type: Journal Article
• Authors: Nanavaty, Vishal; Sandhu, Ranjodh; Jehi, Sanaa E.; Pandya, Unnati M.; Li, Bibo
• Is Part Of: Nucleic acids research. Volume 45:Issue 10(2017)
• Page Start: 5785
• Page End: 5796
• Publication Date: 2017-03-16
• Subjects: Nucleic acids -- Periodicals; Molecular biology -- Periodicals; 572.805
• DOI: 10.1093/nar/gkx184
• Languages: English
• ISSNs: 0305-1048

Abstract

Abstract: Trypanosoma brucei causes human African trypanosomiasis and regularly switches its major surface antigen, VSG, thereby evading the host's immune response. VSGs are monoallelically expressed from subtelomeric expression sites (ESs), and VSG switching exploits subtelomere plasticity. However, subtelomere integrity is essential for T. brucei viability. The telomeric transcript, TERRA, was detected in T. brucei previously. We now show that the active ES-adjacent telomere is transcribed. We find that Tb RAP1, a telomere protein essential for VSG silencing, suppresses VSG gene conversion-mediated switching. Importantly, Tb RAP1 depletion increases the TERRA level, which appears to result from longer read-through into the telomere downstream of the active ES. Depletion of Tb RAP1 also results in more telomeric RNA:DNA hybrids and more double strand breaks (DSBs) at telomeres and subtelomeres. In Tb RAP1-depleted cells, expression of excessive Tb RNaseH1, which cleaves the RNA strand of the RNA:DNA hybrid, brought telomeric RNA:DNA hybrids, telomeric/subtelomeric DSBs and VSG switching frequency back to WT levels. Therefore, Tb RAP1-regulated appropriate levels of TERRA and telomeric RNA:DNA hybrid are fundamental to subtelomere/telomere integrity. Our study revealed for the first time an important role of a long, non-coding RNA in antigenic variation and demonstrated a link between telomeric silencing and subtelomere/telomere integrity through Tb RAP1-regulated telomere transcription.