Subtelomeric Chromatin in the Fission Yeast S. pombe

Abstract

Telomeres play important roles in safeguarding the genome. The specialized repressive chromatin that assembles at telomeres and subtelomeric domains is key to this protective role. However, in many organisms, the repetitive nature of telomeric and subtelomeric sequences has hindered research efforts. The fission yeast S. pombe has provided an important model system for dissection of chromatin biology due to the relative ease of genetic manipulation and strong conservation of important regulatory proteins with higher eukaryotes. Telomeres and the telomere-binding shelterin complex are highly conserved with mammals, as is the assembly of constitutive heterochromatin at subtelomeres. In this review, we seek to summarize recent work detailing the assembly of distinct chromatin structures within subtelomeric domains in fission yeast. These include the heterochromatic SH subtelomeric domains, the telomere-associated sequences (TAS), and ST chromatin domains that assemble highly condensed chromatin clusters called knobs. Specifically, we review new insights into the sequence of subtelomeric domains, the distinct types of chromatin that assemble on these sequences and how histone H3 K36 modifications influence these chromatin structures. We address the interplay between the subdomains of chromatin structure and how subtelomeric chromatin is influenced by both the telomere-bound shelterin complexes and by euchromatic chromatin regulators internal to the subtelomeric domain. Finally, we demonstrate that telomere clustering, which is mediated via the condensed ST chromatin knob domains, does not depend on knob assembly within these domains but on Set2, which mediates H3K36 methylation.

Architecture, Chromatin and Gene Organization of Toxoplasma gondii Subtelomeres

“…In addition, the heterochromatin that forms the ST is characterized by low nucleosome occupancy and the presence of repressive histone marks such as H4K20me3, H3K9me2/3, and H3K27me3. Those marks, in turn, recruit heterochromatin factors such as HP1 and deacetylases such as Sir2, which target H3 and H4 [ 6 , 7 , 8 , 9 ].…”

The Greatwall-Endosulfine-PP2A/B55 pathway controls entry into quiescence by promoting translation of Elongator-tuneable transcripts

“…1b). The heterochromatin present in the subtelomeric regions can be divided into SH chromatin, characterised by highly methylated histone H3K9, and ST chromatin, in which histone modifications are kept at low levels, but exhibit highly condensed chromosome structures called knobs [18][19][20][21][22] . Several protein complexes essential for maintaining the telomeric and subtelomeric structure have been identified.…”

Centromere Positioning Orchestrates Telomere Bouquet Formation and the Initiation of Meiotic Differentiation

“…Conversely, we uncovered substantial defects in transcriptional levels within subtelomeric regions, at both homologous (SH) and unique (ST) chromatin domains [52]. Specifically, we identified noteworthy differences in the transcriptional levels of the proximal subtelomeric regions of chromosomes I and II, which were silenced by heterochromatic pathways [29,54] (Figure 2A and 2B).…”

“…Next, we aimed to investigate the transcriptional state of another crucial specialized chromosome region, in addition to centromeres, which is also finely regulated by silencing factors and tightly connected to the NE-the telomeres. To study possible telomeric regulation defects in Rablcells, we analysed by RT-qPCR the transcription of the telomere-associated sequences (TAS) and the endogenous subtelomeric noncoding RNAs (TERRA, telomeric repeat-containing non-coding RNA) [52]. These experiments revealed no significant changes in the transcription levels of TAS1, TAS2, and TERRA loci, with only a slight increase in TAS3 transcription levels observed in Rabldeficient cells compared to clr4∆ settings (Supplementary 3D and 3E).…”