DNA break site at fragile subtelomeres determines probability and mechanism of antigenic variation in African trypanosomes.

Antigenic variation in African trypanosomes requires monoallelic transcription and switching of variant surface glycoprotein (VSG) genes. The transcribed VSG, always flanked by '70 bp'-repeats and telomeric-repeats, is either replaced through DNA double-strand break (DSB) repair or transcr...

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Autores principales:	Lucy Glover, Sam Alsford, David Horn
Formato:	article
Lenguaje:	EN
Publicado:	Public Library of Science (PLoS) 2013
Materias:	Immunologic diseases. Allergy RC581-607 Biology (General) QH301-705.5
Acceso en línea:	https://doaj.org/article/9d73aee269ae46ddbc96d9dd819b412e
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spelling	oai:doaj.org-article:9d73aee269ae46ddbc96d9dd819b412e2021-11-18T06:05:51ZDNA break site at fragile subtelomeres determines probability and mechanism of antigenic variation in African trypanosomes.1553-73661553-737410.1371/journal.ppat.1003260https://doaj.org/article/9d73aee269ae46ddbc96d9dd819b412e2013-03-01T00:00:00Zhttps://www.ncbi.nlm.nih.gov/pmc/articles/pmid/23555264/?tool=EBIhttps://doaj.org/toc/1553-7366https://doaj.org/toc/1553-7374Antigenic variation in African trypanosomes requires monoallelic transcription and switching of variant surface glycoprotein (VSG) genes. The transcribed VSG, always flanked by '70 bp'-repeats and telomeric-repeats, is either replaced through DNA double-strand break (DSB) repair or transcriptionally inactivated. However, little is known about the subtelomeric DSBs that naturally trigger antigenic variation in Trypanosoma brucei, the subsequent DNA damage responses, or how these responses determine the mechanism of VSG switching. We found that DSBs naturally accumulate close to both transcribed and non-transcribed telomeres. We then induced high-efficiency meganuclease-mediated DSBs and monitored DSB-responses and DSB-survivors. By inducing breaks at distinct sites within both transcribed and silent VSG transcription units and assessing local DNA resection, histone modification, G2/M-checkpoint activation, and both RAD51-dependent and independent repair, we reveal how breaks at different sites trigger distinct responses and, in 'active-site' survivors, different switching mechanisms. At the active site, we find that promoter-adjacent breaks typically failed to trigger switching, 70 bp-repeat-adjacent breaks almost always triggered switching through 70 bp-repeat recombination (∼60% RAD51-dependent), and telomere-repeat-adjacent breaks triggered switching through loss of the VSG expression site (25% of survivors). Expression site loss was associated with G2/M-checkpoint bypass, while 70 bp-repeat-recombination was associated with DNA-resection, γH2A-focus assembly and a G2/M-checkpoint. Thus, the probability and mechanism of antigenic switching are highly dependent upon the location of the break. We conclude that 70 bp-repeat-adjacent and telomere-repeat-adjacent breaks trigger distinct checkpoint responses and VSG switching pathways. Our results show how subtelomere fragility can generate the triggers for the major antigenic variation mechanisms in the African trypanosome.Lucy GloverSam AlsfordDavid HornPublic Library of Science (PLoS)articleImmunologic diseases. AllergyRC581-607Biology (General)QH301-705.5ENPLoS Pathogens, Vol 9, Iss 3, p e1003260 (2013)
institution	DOAJ
collection	DOAJ
language	EN
topic	Immunologic diseases. Allergy RC581-607 Biology (General) QH301-705.5
spellingShingle	Immunologic diseases. Allergy RC581-607 Biology (General) QH301-705.5 Lucy Glover Sam Alsford David Horn DNA break site at fragile subtelomeres determines probability and mechanism of antigenic variation in African trypanosomes.
description	Antigenic variation in African trypanosomes requires monoallelic transcription and switching of variant surface glycoprotein (VSG) genes. The transcribed VSG, always flanked by '70 bp'-repeats and telomeric-repeats, is either replaced through DNA double-strand break (DSB) repair or transcriptionally inactivated. However, little is known about the subtelomeric DSBs that naturally trigger antigenic variation in Trypanosoma brucei, the subsequent DNA damage responses, or how these responses determine the mechanism of VSG switching. We found that DSBs naturally accumulate close to both transcribed and non-transcribed telomeres. We then induced high-efficiency meganuclease-mediated DSBs and monitored DSB-responses and DSB-survivors. By inducing breaks at distinct sites within both transcribed and silent VSG transcription units and assessing local DNA resection, histone modification, G2/M-checkpoint activation, and both RAD51-dependent and independent repair, we reveal how breaks at different sites trigger distinct responses and, in 'active-site' survivors, different switching mechanisms. At the active site, we find that promoter-adjacent breaks typically failed to trigger switching, 70 bp-repeat-adjacent breaks almost always triggered switching through 70 bp-repeat recombination (∼60% RAD51-dependent), and telomere-repeat-adjacent breaks triggered switching through loss of the VSG expression site (25% of survivors). Expression site loss was associated with G2/M-checkpoint bypass, while 70 bp-repeat-recombination was associated with DNA-resection, γH2A-focus assembly and a G2/M-checkpoint. Thus, the probability and mechanism of antigenic switching are highly dependent upon the location of the break. We conclude that 70 bp-repeat-adjacent and telomere-repeat-adjacent breaks trigger distinct checkpoint responses and VSG switching pathways. Our results show how subtelomere fragility can generate the triggers for the major antigenic variation mechanisms in the African trypanosome.
format	article
author	Lucy Glover Sam Alsford David Horn
author_facet	Lucy Glover Sam Alsford David Horn
author_sort	Lucy Glover
title	DNA break site at fragile subtelomeres determines probability and mechanism of antigenic variation in African trypanosomes.
title_short	DNA break site at fragile subtelomeres determines probability and mechanism of antigenic variation in African trypanosomes.
title_full	DNA break site at fragile subtelomeres determines probability and mechanism of antigenic variation in African trypanosomes.
title_fullStr	DNA break site at fragile subtelomeres determines probability and mechanism of antigenic variation in African trypanosomes.
title_full_unstemmed	DNA break site at fragile subtelomeres determines probability and mechanism of antigenic variation in African trypanosomes.
title_sort	dna break site at fragile subtelomeres determines probability and mechanism of antigenic variation in african trypanosomes.
publisher	Public Library of Science (PLoS)
publishDate	2013
url	https://doaj.org/article/9d73aee269ae46ddbc96d9dd819b412e
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DNA break site at fragile subtelomeres determines probability and mechanism of antigenic variation in African trypanosomes.

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