Abstract
BackgroundRNA silencing occurs in a broad range of organisms. Although its ancestral function is probably related to the genome defense mechanism against repetitive selfish elements, it has been found that RNA silencing regulates different cellular processes such as gene expression and chromosomal segregation. In Neurospora crassa, a RNA silencing mechanism, called quelling, acts to repress the expression of transgenes and transposons, but until now no other cellular functions have been shown to be regulated by this mechanism.ResultsHere, we detected by northern blotting endogenous short interfering RNA (siRNAs) from the repetitive ribosomal DNA locus (rDNA) that are loaded onto the argonaute protein QDE-2. Moreover, we found a bidirectional transcription that can generate double strand RNA (dsRNA) molecules. Interestingly, quelling mutants have a reduced rDNA gene copy number.ConclusionOur finding could suggest a new biological function for RNA silencing in the maintenance of the integrity and stability of the Neurospora rDNA locus.
Highlights
RNA silencing occurs in a broad range of organisms
Endogenous siRNAs derived from ribosomal DNA locus (rDNA) repetitive locus In order to investigate whether quelling could target endogenous repetitive sequences, we decided to study the rDNA cluster, the only endogenous long repetitive locus present in Neurospora genome that somehow escaped from Repeated-Induced Point mutation (RIP) [27]
We focused on the Non Transcribed Spacer (NTS) sequence of rDNA locus, which is not normally transcribed for the production of ribosomal RNA (rRNA)
Summary
Its ancestral function is probably related to the genome defense mechanism against repetitive selfish elements, it has been found that RNA silencing regulates different cellular processes such as gene expression and chromosomal segregation. The common intermediate in all silencing phenomena is a dsRNA molecule that is processed by the RNAseIII enzyme Dicer into siRNAs of 21–25 nucleotides in length [1]. These siRNAs are subsequently used as guides by the RNA Induced Silencing Complex (RISC) which contains effector proteins belonging to the Argonaute family that are able to cleave in a sequence specific manner transcripts with sequence complementary to siRNAs [2]. Argonaute's role in transposon silencing is conserved in flies and vertebrates [10,11,12,13]
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