Silencing-associated and meiosis-specific small RNA pathways in Paramecium tetraurelia.
Distinct small RNA pathways are involved in the two types of homology-dependent effects described in Paramecium tetraurelia, as shown by a functional analysis of Dicer and Dicer-like genes and by the sequencing of small RNAs. The siRNAs that mediate post-transcriptional gene silencing when cells are fed with double-stranded RNA (dsRNA) were found to comprise two subclasses. DCR1-dependent cleavage of the inducing dsRNA generates approximately 23-nt primary siRNAs from both strands, while a different subclass of approximately 24-nt RNAs, characterized by a short untemplated poly-A tail, is strictly antisense to the targeted mRNA, suggestive of secondary siRNAs that depend on an RNA-dependent RNA polymerase. An entirely distinct pathway is responsible for homology-dependent regulation of developmental genome rearrangements after sexual reproduction. During early meiosis, the DCL2 and DCL3 genes are required for the production of a highly complex population of approximately 25-nt scnRNAs from all types of germline sequences, including both strands of exons, introns, intergenic regions, transposons and Internal Eliminated Sequences. A prominent 5'-UNG signature, and a minor fraction showing the complementary signature at positions 21-23, indicate that scnRNAs are cleaved from dsRNA precursors as duplexes with 2-nt 3' overhangs at both ends, followed by preferential stabilization of the 5'-UNG strand.
Lepère
Gersende
G
Ecole Normale Supérieure, Laboratoire de Génétique Moléculaire, CNRS, UMR8541, 46 rue d'Ulm, 75005 Paris, France.
Nowacki
Mariusz
M
Serrano
Vincent
V
Gout
Jean-François
JF
Guglielmi
Gérard
G
Duharcourt
Sandra
S
Meyer
Eric
E
D000818:Animals; D003001:Cloning, Molecular; D008540:Meiosis / Q000235:genetics*; D008565:Membrane Proteins / Q000235:genetics; D016805:Paramecium tetraurelia / Q000235:genetics* / Q000378:metabolism; D026723:Polyadenylation; D015800:Protozoan Proteins / Q000235:genetics; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000737:chemistry* / Q000145:classification / Q000378:metabolism; D043244:Ribonuclease III / Q000235:genetics
D008565:Membrane Proteins; C107339:ND7 protein, Protozoa; D015800:Protozoan Proteins; D034741:RNA, Small Interfering; D043244:Ribonuclease III