Trypanosoma brucei RAP1 maintains telomere and subtelomere integrity by suppressing TERRA and telomeric RNA:DNA hybrids.
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 TbRAP1, a telomere protein essential for VSG silencing, suppresses VSG gene conversion-mediated switching. Importantly, TbRAP1 depletion increases the TERRA level, which appears to result from longer read-through into the telomere downstream of the active ES. Depletion of TbRAP1 also results in more telomeric RNA:DNA hybrids and more double strand breaks (DSBs) at telomeres and subtelomeres. In TbRAP1-depleted cells, expression of excessive TbRNaseH1, 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, TbRAP1-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 TbRAP1-regulated telomere transcription.
Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, Cleveland State University, 2121 Euclid Avenue, Cleveland, OH 44115, USA.
Vishal
V
Nanavaty
Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, Cleveland State University, 2121 Euclid Avenue, Cleveland, OH 44115, USA.
Ranjodh
R
Sandhu
Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, Cleveland State University, 2121 Euclid Avenue, Cleveland, OH 44115, USA.
Sanaa E
SE
Jehi
Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, Cleveland State University, 2121 Euclid Avenue, Cleveland, OH 44115, USA.
Unnati M
UM
Pandya
Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, Cleveland State University, 2121 Euclid Avenue, Cleveland, OH 44115, USA.|The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA.|Department of Immunology, Lerner Research Institute, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH 44195, USA.|Case Comprehensive Cancer Center, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA.
Bibo
B
Li
D020029:Base Pairing; D053903:DNA Breaks, Double-Stranded; D016054:DNA, Protozoan / Q000235:genetics* / Q000378:metabolism; D009693:Nucleic Acid Hybridization; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism; D062085:RNA, Long Noncoding / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D016053:RNA, Protozoan / Q000235:genetics* / Q000378:metabolism; D016914:Ribonuclease H / Q000235:genetics / Q000378:metabolism; D016615:Telomere / Q000737:chemistry* / Q000378:metabolism; D014158:Transcription, Genetic; D014346:Trypanosoma brucei brucei / Q000235:genetics* / Q000378:metabolism; D014643:Variant Surface Glycoproteins, Trypanosoma / Q000235:genetics* / Q000378:metabolism; D020827:rap1 GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism
D016054:DNA, Protozoan; D015800:Protozoan Proteins; D062085:RNA, Long Noncoding; D012333:RNA, Messenger; D016053:RNA, Protozoan; D014643:Variant Surface Glycoproteins, Trypanosoma; D016914:Ribonuclease H; C078856:ribonuclease HI; D020827:rap1 GTP-Binding Proteins