title: snRNA-specific role of SMN in trypanosome snRNP biogenesis in vivo.
abstract: Pre-mRNA splicing in trypanosomes requires the SMN-mediated assembly of small nuclear ribonucleoproteins (snRNPs). In contrast to higher eukaryotes, the cellular localization of snRNP biogenesis and the involvement of nuclear-cytoplasmic trafficking in trypanosomes are controversial. By using RNAi knockdown of SMN in T. brucei to investigate its functional role in snRNP assembly, we found dramatic changes in the steady-state levels of snRNAs and snRNPs: The SL RNA accumulates, whereas U1, U4, and U5 snRNA levels decrease, and Sm core assembly in particular of the SL RNA is strongly reduced. In addition, SMN depletion blocks U4/U6 di-snRNP formation; the variant Sm core of the U2 snRNP, however, still forms efficiently after SMN knockdown. Concerning the longstanding question, whether nuclear-cytoplasmic trafficking is involved in trypanosomal snRNP biogenesis, fluorescence in situ hybridization (FISH) and immunofluorescence assays revealed that the SL RNA genes and transcripts colocalize with SMN. Remarkably, SMN silencing leads to a nucleoplasmic accumulation of both SL RNA and the Sm proteins. In sum, our data demonstrate an essential and snRNA-selective role of SMN in snRNP biogenesis in vivo and strongly argue for a nucleoplasmic Sm core assembly of the SL RNP.
authors.affiliation: Institut für Biochemie, Justus-Liebig-Universität Gießen, Gießen, Germany.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Jaé
authors.forename: Christian
authors.initials: C
authors.lastname: Preusser
authors.forename: Timothy
authors.initials: T
authors.lastname: Krüger
authors.forename: Itai Dov
authors.initials: ID
authors.lastname: Tkacz
authors.forename: Markus
authors.initials: M
authors.lastname: Engstler
authors.forename: Shulamit
authors.initials: S
authors.lastname: Michaeli
authors.forename: Albrecht
authors.initials: A
authors.lastname: Bindereif
mesh_terms: D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D005455:Fluorescent Antibody Technique; D005786:Gene Expression Regulation; D055785:Gene Knockdown Techniques; D056426:Genetic Loci; D017404:In Situ Hybridization, Fluorescence; D034622:RNA Interference; D012326:RNA Splicing; D016053:RNA, Protozoan / Q000235:genetics / Q000378:metabolism*; D012342:RNA, Small Nuclear / Q000032:analysis / Q000378:metabolism*; D020038:RNA, Spliced Leader / Q000378:metabolism; D017411:Ribonucleoproteins, Small Nuclear / Q000378:metabolism*; D055532:SMN Complex Proteins / Q000235:genetics / Q000378:metabolism*; D014346:Trypanosoma brucei brucei / Q000235:genetics* / Q000378:metabolism
chemical_list: D016053:RNA, Protozoan; D012342:RNA, Small Nuclear; D020038:RNA, Spliced Leader; D017411:Ribonucleoproteins, Small Nuclear; D055532:SMN Complex Proteins