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Dynamic colocalization of 2 simultaneously active VSG expression sites within a single expression-site body in Trypanosoma brucei

Budzak, James, Kerry, Louise E., Aristodemou, Aris, Hall, Belinda S., Witmer, Kathrin, Kushwaha, Manish, Davies, Carys, Povelones, Megan L., McDonald, Jacquelyn R., Sur, Aakash , Myler, Peter J. and Rudenko, Gloria (2019) Dynamic colocalization of 2 simultaneously active VSG expression sites within a single expression-site body in Trypanosoma brucei Proceedings of the National Academy of Sciences, 116 (33). pp. 16561-16570.

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Monoallelic exclusion ensures that the African trypanosome Trypanosoma brucei exclusively expresses only 1 of thousands of different variant surface glycoprotein (VSG) coat genes. The active VSG is transcribed from 1 of 15 polycistronic bloodstream-form VSG expression sites (ESs), which are controlled in a mutually exclusive fashion. Unusually, T. brucei uses RNA polymerase I (Pol I) to transcribe the active ES, which is unprecedented among eukaryotes. This active ES is located within a unique extranucleolar Pol I body called the expression-site body (ESB). A stringent restriction mechanism prevents T. brucei from expressing multiple ESs at the same time, although how this is mediated is unclear. By using drug-selection pressure, we generated VSG double-expresser T. brucei lines, which have disrupted monoallelic exclusion, and simultaneously express 2 ESs in a dynamic fashion. The 2 unstably active ESs appear epigenetically similar to fully active ESs as determined by using chromatin immunoprecipitation for multiple epigenetic marks (histones H3 and H1, TDP1, and DNA base J). We find that the double-expresser cells, similar to wild-type single-expresser cells, predominantly contain 1 subnuclear ESB, as determined using Pol I or the ESB marker VEX1. Strikingly, simultaneous transcription of the 2 dynamically transcribed ESs is normally observed only when the 2 ESs are both located within this single ESB. This colocalization is reversible in the absence of drug selection. This discovery that simultaneously active ESs dynamically share a single ESB demonstrates the importance of this unique subnuclear body in restricting the monoallelic expression of VSG.

Item Type: Article
Divisions : Faculty of Health and Medical Sciences > School of Biosciences and Medicine
Authors :
Budzak, James
Kerry, Louise E.
Aristodemou, Aris
Hall, Belinda
Witmer, Kathrin
Kushwaha, Manish
Davies, Carys
Povelones, Megan L.
McDonald, Jacquelyn R.
Sur, Aakash
Myler, Peter J.
Rudenko, Gloria
Date : 29 July 2019
Funders : Biotechnology and Biological Sciences Research Council (BBSRC), Wellcome Trust, National Institute of Allergy and Infectious Diseases
DOI : 10.1073/pnas.1905552116
Grant Title : DTP PhD studentship
Copyright Disclaimer : Copyright © 2019 the Author(s). Published by PNAS. This open access article is distributed under Creative Commons Attribution License 4.0 (CC BY).
Uncontrolled Keywords : variant surface glycoprotein; RNA polymerase I; Antigenic variation; Epigenetics; Monoallelic exclusion
Depositing User : Clive Harris
Date Deposited : 12 Sep 2019 15:09
Last Modified : 12 Sep 2019 15:09

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