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RNA expression profiling for Paf1 complex mutant strains [mRNA]

ABSTRACT: Small RNA molecules are well known for silencing gene expression post-transcriptionally, but they are also implicated in epigenetic regulation across kingdoms. However, the mechanisms of epigenetic gene silencing by small RNAs are mostly unknown. In addition, stably silencing genes de novo using synthetic small RNAs to trigger locus-independent heterochromatin formation is impossible. Using fission yeast, we show that RNA-directed heterochromatin formation is negatively controlled by the highly conserved RNA polymerase-associated factor 1 (Paf1) complex. Temporary expression of a synthetic hairpin RNA in Paf1 mutants triggers stable heterochromatin formation at homologous loci, effectively silencing genes in trans. This repressed state is propagated over many generations by continual production of secondary siRNAs, independently of the synthetic hairpin RNA. Our work uncovers a novel mechanism for small RNA-mediated epigenome regulation and highlights fundamental roles for the Paf1 complex and the RNA interference machinery in building epigenetic memory.

ORGANISM(S): Schizosaccharomyces pombe

PROVIDER: GSE59169 | GEO | 2015/03/25

SECONDARY ACCESSION(S): PRJNA254526

REPOSITORIES: GEO

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Project description:Small RNAs are the common denominator of various RNA silencing pathways that regulate gene expression and protect the genome against mobile repetitive DNA sequences, retroelements, and transposons. In Schizosaccharomyces pombe, small interfering RNAs (siRNAs) are required for the faithful propagation of heterochromatin that is found at peri-centromeric repeats. In contrast to repetitive DNA, protein-coding genes are refractory to siRNA-mediated heterochromatin formation, unless siRNAs are expressed in mutant cells. Different studies have shown that siRNAs become potent mediators of RNAi-mediated epigenetic gene silencing in S. pombe cells that are mutant for mlo3+, dss1+, mst2+, or genes encoding subunits of the Paf1 complex (Paf1C). In this study, we have combined chemical mutagenesis with whole-genome sequencing in a sensitized S. pombe reporter strain to obtain a more comprehensive list of putative suppressors of small-RNA-mediated epigenetic gene silencing. This revealed more than 20 novel silencing-enabling mutations in genes that are associated with RNA processing, regulation of transcription, or post-translational protein modification. Focusing on factors involved in pre-mRNA cleavage and polyadenylation, we for example show that single amino acid substitutions in Yth1, which is responsible for polyadenylation signal recognition, lead to nearly 100% effective de novo formation of silent heterochromatin. In S. pombe, small RNA-mediated silencing relies on the continuous amplification of the siRNA pool through a positive feedback loop. The deposited data shows the generation of secondary small RNAs over the reporter gene exclusively in the presence of RNAi-enabling mutations in the pre-mRNA cleavage and polyadenylation machinery. Furthermore, the RNA-seq data show that overall transcriptome levels are not markedly changing in the mutations themselves. Altogether, our work shows that epigenetic gene silencing can be enabled by the acquisition of a plethora of mutant alleles in fission yeast.

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RNA expression profiling for Paf1 complex mutant strains [mRNA]

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