Nuclear repositioning of the VSG promoter during developmental silencing in Trypanosoma brucei

Interphase nuclear repositioning of chromosomes has been implicated in the epigenetic regulation of RNA polymerase (pol) II transcription. However, little is known about the nuclear position–dependent regulation of RNA pol I–transcribed loci. Trypanosoma brucei is an excellent model system to address this question because its two main surface protein genes, procyclin and variant surface glycoprotein (VSG), are transcribed by pol I and undergo distinct transcriptional activation or downregulation events during developmental differentiation. Although the monoallelically expressed VSG locus is exclusively localized to an extranucleolar body in the bloodstream form, in this study, we report that nonmutually exclusive procyclin genes are located at the nucleolar periphery. Interestingly, ribosomal DNA loci and pol I transcription activity are restricted to similar perinucleolar positions. Upon developmental transcriptional downregulation, however, the active VSG promoter selectively undergoes a rapid and dramatic repositioning to the nuclear envelope. Subsequently, the VSG promoter region was subjected to chromatin condensation. We propose a model whereby the VSG expression site pol I promoter is selectively targeted by temporal nuclear repositioning during developmental silencing.

[1]  M. Okuwaki,et al.  [Structure and function of the nucleolus]. , 2006, Tanpakushitsu kakusan koso. Protein, nucleic acid, enzyme.

[2]  G. Cross,et al.  Selective di- or trimethylation of histone H3 lysine 76 by two DOT1 homologs is important for cell cycle regulation in Trypanosoma brucei. , 2006, Molecular cell.

[3]  Christine Clayton,et al.  A doubly inducible system for RNA interference and rapid RNAi plasmid construction in Trypanosoma brucei. , 2005, Molecular and biochemical parasitology.

[4]  S. Gasser,et al.  Sir-Mediated Repression Can Occur Independently of Chromosomal and Subnuclear Contexts , 2004, Cell.

[5]  Markus Engstler,et al.  Cold shock and regulation of surface protein trafficking convey sensitization to inducers of stage differentiation in Trypanosoma brucei. , 2004, Genes & development.

[6]  A. Belmont,et al.  Differential large-scale chromatin compaction and intranuclear positioning of transcribed versus non-transcribed transgene arrays containing β-globin regulatory sequences , 2004, Journal of Cell Science.

[7]  L. Vanhamme,et al.  Antigenic variation in Trypanosoma brucei: facts, challenges and mysteries. , 2004, Current opinion in microbiology.

[8]  G. Cross,et al.  Telomere length regulation and transcriptional silencing in KU80-deficient Trypanosoma brucei. , 2004, Nucleic acids research.

[9]  D. Spector,et al.  The dynamics of chromosome organization and gene regulation. , 2003, Annual review of biochemistry.

[10]  N. Robinson,et al.  Ku Is Important for Telomere Maintenance, but Not for Differential Expression of Telomeric VSG Genes, in African Trypanosomes* , 2002, The Journal of Biological Chemistry.

[11]  S. Gasser,et al.  Visualizing Chromatin Dynamics in Interphase Nuclei , 2002, Science.

[12]  P. Borst.  Antigenic Variation and Allelic Exclusion , 2002, Cell.

[13]  Keith Gull,et al.  A pol I transcriptional body associated with VSG mono-allelic expression in Trypanosoma brucei , 2001, Nature.

[14]  J. Barry,et al.  Antigenic variation in trypanosomes: enhanced phenotypic variation in a eukaryotic parasite. , 2001, Advances in parasitology.

[15]  R. Cole,et al.  The Procyclin Repertoire of Trypanosoma brucei , 1999, The Journal of Biological Chemistry.

[16]  G. Cross,et al.  Trypanosoma brucei variant surface glycoprotein regulation involves coupled activation/inactivation and chromatin remodeling of expression sites , 1999, The EMBO journal.

[17]  G. Cross,et al.  Trypanosoma brucei , 1998 .

[18]  P. Borst,et al.  Subnuclear localization of the active variant surface glycoprotein gene expression site in Trypanosoma brucei. , 1998, Proceedings of the National Academy of Sciences of the United States of America.

[19]  C. Clayton,et al.  PARP gene expression: control at many levels. , 1998, Molecular and biochemical parasitology.

[20]  G. Cross,et al.  Regulation of vsg expression site transcription and switching in Trypanosoma brucei. , 1998, Molecular and biochemical parasitology.

[21]  A S Belmont,et al.  In vivo localization of DNA sequences and visualization of large-scale chromatin organization using lac operator/repressor recognition , 1996, The Journal of cell biology.

[22]  Andrew W. Murray,et al.  GFP tagging of budding yeast chromosomes reveals that protein–protein interactions can mediate sister chromatid cohesion , 1996, Current Biology.

[23]  G. Cross,et al.  A developmentally regulated position effect at a telomeric locus in Trypanosoma brucei , 1995, Cell.

[24]  L. Vanhamme,et al.  The 3′‐terminal region of the mRNAs for VSG and procyclin can confer stage specificity to gene expression in Trypanosoma brucei. , 1995, The EMBO journal.

[25]  L. V. D. van der Ploeg,et al.  RNA polymerase I-mediated protein-coding gene expression in Trypanosoma brucei. , 1992, Parasitology today.

[26]  G. Rudenko,et al.  RNA polymerase I can mediate expression of CAT and neo protein‐coding genes in Trypanosoma brucei. , 1991, The EMBO journal.

[27]  G. Rudenko,et al.  Procyclic acidic repetitive protein (PARP) genes located in an unusually small alpha-amanitin-resistant transcription unit: PARP promoter activity assayed by transient DNA transfection of Trypanosoma brucei , 1990, Molecular and cellular biology.

[28]  H. Schwarz,et al.  Procyclin gene expression and loss of the variant surface glycoprotein during differentiation of Trypanosoma brucei , 1989, The Journal of cell biology.

[29]  P. Overath,et al.  The effect of citrate/cis-aconitate on oxidative metabolism during transformation of Trypanosoma brucei. , 1986, European journal of biochemistry.