title: Nowa1p and Nowa2p: novel putative RNA binding proteins involved in trans-nuclear crosstalk in Paramecium tetraurelia.
abstract: BACKGROUND
  The germline genome of ciliates is extensively rearranged during development of a new somatic macronucleus from the germline micronucleus, a process that follows sexual events. In Paramecium tetraurelia, single-copy internal eliminated sequences (IESs) and multicopy transposons are eliminated, whereas cellular genes are amplified to approximately 800 n. For a subset of IESs, introduction of the IES sequence into the maternal (prezygotic) macronucleus specifically inhibits excision of the homologous IES in the developing zygotic macronucleus. This and other homology-dependent maternal effects have suggested that rearrangement patterns are epigenetically determined by an RNA-mediated, trans-nuclear comparison, involving the RNA interference pathway, of germline and somatic genomes.
  
  
  RESULTS
  We report the identification of novel developmentally regulated RNA binding proteins, Nowa1p and Nowa2p, which are required for the survival of sexual progeny. Green fluorescent protein (GFP) fusions show that Nowa1p accumulates into the maternal macronucleus shortly before meiosis of germline micronuclei and is later transported to developing macronuclei. Nowa1p/2p depletion impairs the elimination of transposons and of those IESs that are controlled by maternal effects, confirming the existence of distinct IES classes.
  
  
  CONCLUSIONS
  The results indicate that Nowa proteins are essential components of the trans-nuclear-crosstalk mechanism that is responsible for epigenetic programming of genome rearrangements. We discuss implications for the current models of genome scanning in ciliates, a process related to the formation of heterochromatin by RNA interference in other eukaryotes.
authors.affiliation: Laboratoire de Génétique Moléculaire, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 8541, Ecole Normale Supérieure, 46 rue d'Ulm, 75005 Paris, France.
authors.forename: Mariusz
authors.initials: M
authors.lastname: Nowacki
authors.forename: Wlodzimierz
authors.initials: W
authors.lastname: Zagorski-Ostoja
authors.forename: Eric
authors.initials: E
authors.lastname: Meyer
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D044127:Epigenesis, Genetic / Q000235:genetics / Q000502:physiology*; D017353:Gene Deletion; D015321:Gene Rearrangement / Q000235:genetics / Q000502:physiology*; D049452:Green Fluorescent Proteins; D048648:Macronucleus / Q000235:genetics / Q000378:metabolism*; D048631:Micronucleus, Germline / Q000235:genetics / Q000378:metabolism*; D015336:Molecular Probe Techniques; D008969:Molecular Sequence Data; D009841:Oligonucleotides; D016805:Paramecium tetraurelia / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D034622:RNA Interference; D016601:RNA-Binding Proteins / Q000378:metabolism*; D012098:Reproduction / Q000235:genetics
chemical_list: D009841:Oligonucleotides; D016601:RNA-Binding Proteins; D049452:Green Fluorescent Proteins