Dynamic colocalization of 2 simultaneously active VSG expression sites within a single expression-site body in Trypanosoma brucei
Author(s)
Type
Journal Article
Abstract
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.
Date Issued
2019-08-13
Date Acceptance
2019-07-02
Citation
Proceedings of the National Academy of Sciences of the United States of America, 2019, 116 (33), pp.16561-16570
ISSN
0027-8424
Publisher
National Academy of Sciences
Start Page
16561
End Page
16570
Journal / Book Title
Proceedings of the National Academy of Sciences of the United States of America
Volume
116
Issue
33
Copyright Statement
© 2019 the Author(s). Published by PNAS.
This open access article is distributed under Creative Commons Attribution License 4.0 (CC BY) (http://creativecommons.org/licenses/by/4.0/).
This open access article is distributed under Creative Commons Attribution License 4.0 (CC BY) (http://creativecommons.org/licenses/by/4.0/).
Sponsor
Wellcome Trust
Identifier
http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000481404300063&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=1ba7043ffcc86c417c072aa74d649202
Grant Number
212211/Z/18/Z
Subjects
Science & Technology
Multidisciplinary Sciences
Science & Technology - Other Topics
variant surface glycoprotein
RNA polymerase I
antigenic variation
epigenetics
monoallelic exclusion
VARIANT SURFACE GLYCOPROTEIN
RNA-POLYMERASE-I
GENE-EXPRESSION
ANTIGENIC VARIATION
MONOALLELIC EXPRESSION
BASE J
TRANSCRIPTION
LOCALIZATION
HYDROXYMETHYLURACIL
ORGANIZATION
Publication Status
Published
Date Publish Online
2019-07-29