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RNAi mediates allele-specific epigenetic inheritance of heterochromatin [ncRNA-seq]

ABSTRACT: We tested the ability of trans siRNAs to establish a silent allele of endogenous ade6+ or an ade6+ transgene inserted within euchromatic loci. We found that a silent ade6-OFF epi-allele that grows red on low adenine medium could be established in several mutant backgrounds (mlo3∆, leo1∆) in the presence of ectopic siRNAs. Furthermore, we found that the silent ade6-OFF epi-allele could be meiotically inherited to wildtype progeny lacking the establishing mutation or ectopic siRNAs. Here, we sequenced genome-wide small RNAs and found widespread generation of secondary siRNAs at genes surrounding the ade6-OFF locus in cells expressing the ectopic siRNAs source cen::ade6. In wildtype meiotic progeny lacking the driver cen::ade6 siRNAs, we observed establishment of a local siRNA producing locus at genes adjacent to the endogenous ade6-OFF or at a kanMX-ade6-OFF transgene inserted within euchromatic loci. In contrast, spreading of secondary siRNAs was limited or nonexistent in ade6-ON cells. Finally, we found that spreading of secondary siRNAs at the endogenous ade6 locus was limited when an ade6 hairpin construct served as the ectopic siRNA driver locus instead of cen::ade6.

ORGANISM(S): Schizosaccharomyces pombe

PROVIDER: GSE111858 | GEO | 2018/04/26

REPOSITORIES: GEO

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Project description:The centromere is defined by the presence of a centromere-specific histone H3 variant, CENH3. Establishment and maintenance of the centromeric chromatin (CEN chromatin) is determined by poorly understood epigenetic mechanisms. Interestingly, CEN chromatin in several eukaryotes showed euchromatic characteristics although being embedded within pericentromeric heterochromatin. Specifically, H3K4me2 appeared to be a unique histone modification mark associated with animal centromeres. We developed a genomic tiling array for four fully sequenced rice centromeres. A ChIP-chip approach was used to study the patterns of several euchromatic histone modification marks, including H3K4me2, H3K4me3, H3K36me3, and H3K4K9a, associated with rice centromeres. We demonstrate that the CENH3 subdomains within the four centromeres are depleted with the four histone H3 marks. The vast majority of the four histone marks were associated with the genes located in the H3 subdomains within the centromeric cores. Genes in the centromeres showed similar histone modification patterns as those located outside of the centromeres. Thus, the euchromatic characteristics of rice CEN chromatin are trademarks of the transcribed sequences embedded in the H3 subdomains of the centromeres. We propose that the constitutively expressed genes located in rice centromeres may provide a barrier for loading of CENH3 into the H3 subdomains. The separation of CENH3 into the H3 subdomains is favorable for the three dimensional structure and its associated function of rice centromeres. We developed a genomic tiling array that covers four rice centromeres (Cen4, Cen5, Cen7, and Cen8) using the NimbleGen 3x720K array based on the NimbleGen HD2 platform. We used four antibodies (H3K4me3, H3K4me2, H3K36me3, H3K4K9ac) to perform ChIP-chip experiments. ChIP was conducted using leaf tissue from two-week old rice seedlings. We have 3 biological replicates for each antibody and 6 technological replicates of hybridization with position exchange on the array. Thus, each histone modification included 18 hybridization experiments.

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RNAi mediates allele-specific epigenetic inheritance of heterochromatin [ncRNA-seq]

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