title: The 5' spreading of small RNAs in Dictyostelium discoideum depends on the RNA-dependent RNA polymerase RrpC and on the dicer-related nuclease DrnB.
abstract: RNA interference (RNAi) is a gene-regulatory mechanism in eukarya that is based on the presence of double stranded RNA and that can act on both, the transcription or post-transcriptional level. In many species, RNA-dependent RNA polymerases (RdRPs) are required for RNAi. To study the function of the three RdRPs in the amoeba Dictyostelium discoideum, we have deleted the encoding genes rrpA, rrpB and rrpC in all possible combinations. In these strains, expression of either antisense or hairpin RNA constructs against the transgene lacZ resulted in a 50% reduced β-Galactosidase activity. Northern blots surprisingly revealed unchanged lacZ mRNA levels, indicative of post-transcriptional regulation. Only in rrpC knock out strains, low levels of β-gal small interfering RNAs (siRNAs) could be detected in antisense RNA expressing strains. In contrast to this, and at considerably higher levels, all hairpin RNA expressing strains featured β-gal siRNAs. Spreading of the silencing signal to mRNA sequences 5' of the original hairpin trigger was observed in all strains, except when the rrpC gene or that of the dicer-related nuclease DrnB was deleted. Thus, our data indicate that transitivity of an RNA silencing signal exists in D. discoideum and that it requires the two enzymes RrpC and DrnB.
authors.affiliation: Ribogenetics@Biochemistry Lab, School of Engineering and Science, MOLIFE Research Center, Jacobs University Bremen, Bremen, Germany.
authors.forename: Stephan
authors.initials: S
authors.lastname: Wiegand
authors.forename: Christian
authors.initials: C
authors.lastname: Hammann
mesh_terms: D004023:Dictyostelium / Q000235:genetics* / Q000378:metabolism*; D017353:Gene Deletion; D015870:Gene Expression; D005786:Gene Expression Regulation; D020868:Gene Silencing; D017930:Genes, Reporter; D034622:RNA Interference; D016372:RNA, Antisense / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics* / Q000378:metabolism; D012324:RNA-Dependent RNA Polymerase / Q000378:metabolism*; D043244:Ribonuclease III / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D016372:RNA, Antisense; D034741:RNA, Small Interfering; D012324:RNA-Dependent RNA Polymerase; D043244:Ribonuclease III