Hexanucleotide motifs mediate recruitment of the RNA elimination machinery to silent meiotic genes

The selective elimination system blocks the accumulation of meiosis-specific mRNAs during the mitotic cell cycle in fission yeast. These mRNAs harbour a region, the determinant of selective removal (DSR), which is recognized by a YTH-family RNA-binding protein, Mmi1. Mmi1 directs target transcripts to destruction in association with nuclear exosomes. Hence, the interaction between DSR and Mmi1 is crucial to discriminate mitosis from meiosis. Here, we show that Mmi1 interacts with repeats of the hexanucleotide U(U/C)AAAC that are enriched in the DSR. Disruption of this ‘DSR core motif’ in a target mRNA inhibits its elimination. Tandem repeats of the motif can function as an artificial DSR. Mmi1 binds to it in vitro. Thus, a core motif cluster is responsible for the DSR activity. Furthermore, certain variant hexanucleotide motifs can augment the function of the DSR core motif. Notably, meiRNA, which composes the nuclear Mei2 dot required to suppress Mmi1 activity during meiosis, carries numerous copies of the core/augmenting motifs on its tail and is indeed degraded by the Mmi1/exosome system, indicating its likely role as decoy bait for Mmi1

Destabilizing heterochromatin: Does Swi6/HP1 make the choice?

International audienceHP1 is well known as a key silencing protein. However, in the June 9 issue of Molecular Cell, report that Swi6/HP1 recruits an antisilencing protein, Epe1, to facilitate transcription, leading to a model in which Swi6/HP1 is used as a platform to recruit both silencing and antisilencing activities

Long noncoding RNA-based chromatin control of germ cell differentiation: a yeast perspective

Germ cell differentiation, the cellular process by which a diploid progenitor cell produces by meiotic divisions haploid cells, is conserved from the unicellular yeasts to mammals. Over the recent years, yeast germ cell differentiation process has proven to be a powerful biological system to identify and study several long noncoding RNAs (lncRNAs) that play a central role in regulating cellular differentiation by acting directly on chromatin. Remarkably, in the well-studied budding yeast Saccharomyces cerevisiae and fission yeast Schizosaccharomyces pombe, the lncRNA-based chromatin regulations of germ cell differentiation are quite different. In this review, we present an overview of these regulations by focusing on the mechanisms and their respective functions both in S. cerevisiae and in S. pombe. Part of these lncRNA-based chromatin regulations may be conserved in other eukaryotes and play critical roles either in the context of germ cell differentiation or, more generally, in the development of multicellular organisms

Identification de la famille d'histones désacétylases (HDACs) de classe II (études fonctionnelles de mHDAC-5, -6 et -7)

GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

RNAi-directed assembly of heterochromatin in fission yeast.

International audienceHeterochromatin is an epigenetically heritable and conserved feature of eukaryotic chromosomes with important roles in chromosome segregation, genome stability, and gene regulation. The formation of heterochromatin involves an ordered array of chromatin changes, including histone deacetylation, histone H3-lysine 9 methylation, and recruitment of histone binding proteins such as Swi6/HP1. Recent discoveries have uncovered a role for the RNA interference (RNAi) pathway in heterochromatin assembly in the fission yeast Schizosaccharomyces pombe and other eukaryotes. Purification of two RNAi complexes, RITS and RDRC, from fission yeast has provided further insight into the mechanism of RNAi-mediated heterochromatin assembly. These discoveries have given rise to a model in which small interfering RNA molecules act as specificity factors that initiate epigenetic chromatin modifications and double strand RNA synthesis at specific chromosome regions

Labeling and characterization of small RNAs associated with the RNA interference effector complex RITS.

International audienceRNA interference (RNAi) is a gene silencing mechanism that acts at both the posttranscriptional and transcriptional levels. We have recently identified an RNA-containing complex, named RNA-induced transcriptional silencing (RITS), that directly links RNAi to transcriptional gene silencing in Schizosaccharomyces pombe. Here we review the affinity purification methods we use to isolate RITS and describe how to purify, detect, and analyze RNAs associated with this complex

Tethering RITS to a Nascent Transcript Initiates RNAi-and Heterochromatin- Dependent Gene Silencing

SUMMARY In the fission yeast Schizosaccharomyces pombe, the RNA-Induced Transcriptional Silencing (RITS) complex has been proposed to target the chromosome via siRNA-dependent base-pairing interactions to initiate heterochromatin formation. Here we show that tethering of the RITS subunit, Tas3, to the RNA transcript of the normally active ura4 + gene silences ura4 + expression. This silencing depends on a functional RNAi pathway, requires the heterochromatin proteins, Swi6/HP1, Clr4/Suv39h, and Sir2, and is accompanied by the generation of ura4 + siRNAs, histone H3-lysine 9 methylation, and Swi6 binding. Furthermore, the ability of the newly generated ura4 + siRNAs to silence a second ura4 + allele in trans is strongly inhibited by the conserved siRNA nuclease, Eri1. Surprisingly, silencing of tethered ura4 + , or ura4 + inserted within centromeric heterochromatin, or some of the endogenous centromeric repeat promoters, is not associated with changes in RNA polymerase II occupancy. These findings support a model in which targeting of nascent transcripts by RITS mediates chromatin modifications and suggest that cotranscriptional processing events play a primary role in the silencing mechanism