title: NUP-1 Is a large coiled-coil nucleoskeletal protein in trypanosomes with lamin-like functions.
abstract: A unifying feature of eukaryotic nuclear organization is genome segregation into transcriptionally active euchromatin and transcriptionally repressed heterochromatin. In metazoa, lamin proteins preserve nuclear integrity and higher order heterochromatin organization at the nuclear periphery, but no non-metazoan lamin orthologues have been identified, despite the likely presence of nucleoskeletal elements in many lineages. This suggests a metazoan-specific origin for lamins, and therefore that distinct protein elements must compose the nucleoskeleton in other lineages. The trypanosomatids are highly divergent organisms and possess well-documented but remarkably distinct mechanisms for control of gene expression, including polycistronic transcription and trans-splicing. NUP-1 is a large protein localizing to the nuclear periphery of Trypanosoma brucei and a candidate nucleoskeletal component. We sought to determine if NUP-1 mediates heterochromatin organization and gene regulation at the nuclear periphery by examining the influence of NUP-1 knockdown on morphology, chromatin positioning, and transcription. We demonstrate that NUP-1 is essential and part of a stable network at the inner face of the trypanosome nuclear envelope, since knockdown cells have abnormally shaped nuclei with compromised structural integrity. NUP-1 knockdown also disrupts organization of nuclear pore complexes and chromosomes. Most significantly, we find that NUP-1 is required to maintain the silenced state of developmentally regulated genes at the nuclear periphery; NUP-1 knockdown results in highly specific mis-regulation of telomere-proximal silenced variant surface glycoprotein (VSG) expression sites and procyclin loci, indicating a disruption to normal chromatin organization essential to life-cycle progression. Further, NUP-1 depletion leads to increased VSG switching and therefore appears to have a role in control of antigenic variation. Thus, analogous to vertebrate lamins, NUP-1 is a major component of the nucleoskeleton with key roles in organization of the nuclear periphery, heterochromatin, and epigenetic control of developmentally regulated loci.
authors.affiliation: Department of Pathology, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Kelly N
authors.initials: KN
authors.lastname: DuBois
authors.forename: Sam
authors.initials: S
authors.lastname: Alsford
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Holden
authors.forename: Johanna
authors.initials: J
authors.lastname: Buisson
authors.forename: Michal
authors.initials: M
authors.lastname: Swiderski
authors.forename: Jean-Mathieu
authors.initials: JM
authors.lastname: Bart
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Ratushny
authors.forename: Yakun
authors.initials: Y
authors.lastname: Wan
authors.forename: Philippe
authors.initials: P
authors.lastname: Bastin
authors.forename: J David
authors.initials: JD
authors.lastname: Barry
authors.forename: Miguel
authors.initials: M
authors.lastname: Navarro
authors.forename: David
authors.initials: D
authors.lastname: Horn
authors.forename: John D
authors.initials: JD
authors.lastname: Aitchison
authors.forename: Michael P
authors.initials: MP
authors.lastname: Rout
authors.forename: Mark C
authors.initials: MC
authors.lastname: Field
mesh_terms: D000940:Antigenic Variation; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D002875:Chromosomes / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D055785:Gene Knockdown Techniques; D017125:Genes, Protozoan; D056426:Genetic Loci; D006570:Heterochromatin / Q000235:genetics / Q000378:metabolism; D034882:Lamins / Q000235:genetics / Q000378:metabolism*; D046529:Microscopy, Electron, Transmission; D008938:Mitosis; D009685:Nuclear Envelope / Q000235:genetics / Q000378:metabolism*; D028861:Nuclear Pore Complex Proteins; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D021381:Protein Transport; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D016615:Telomere / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D014346:Trypanosoma brucei brucei / Q000166:cytology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D014643:Variant Surface Glycoproteins, Trypanosoma / Q000235:genetics / Q000378:metabolism
chemical_list: D006570:Heterochromatin; D034882:Lamins; D028861:Nuclear Pore Complex Proteins; D009687:Nuclear Proteins; D015800:Protozoan Proteins; D014643:Variant Surface Glycoproteins, Trypanosoma