Coupling Between Sequence-Mediated Nucleosome Organization and Genome Evolution

Barbier, Jérémy; Vaillant, Cédric; Volff, Jean‐Nicolas; Brunet, Frédéric; Audit, Benjamin

doi:10.20944/preprints202105.0166.v1

Cited by 5 publications

(1 citation statement)

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“…In yeast and human, actively transcribed genes tend to have shorter NRL than transcriptionally inactive genes, partially due to the binding of H1 generating inaccessible chromatin at inactive genes (47,55,56). With the separation of the germline MIC and the somatic MAC genomes in two distinct nuclei, the Paramecium MAC genome is very compact.…”

Section: Discussionmentioning

confidence: 99%

GC content, but not nucleosome positioning, directly contributes to intron splicing efficiency in Paramecium

et al. 2022

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Eukaryotic genes are interrupted by introns that must be accurately spliced from mRNA precursors. With an average length of 25 nt, the more than 90,000 introns of Paramecium tetraurelia stand among the shortest introns reported in eukaryotes. The mechanisms specifying the correct recognition of these tiny introns remain poorly understood. Splicing can occur cotranscriptionally, and it has been proposed that chromatin structure might influence splice site recognition. To investigate the roles of nucleosome positioning in intron recognition, we determined the nucleosome occupancy along the P. tetraurelia genome. We show that P. tetraurelia displays a regular nucleosome array with a nucleosome repeat length of ∼151 bp, among the smallest periodicities reported. Our analysis has revealed that introns are frequently associated with inter-nucleosomal DNA, pointing to an evolutionary constraint favoring introns at the AT-rich nucleosome edge sequences. Using accurate splicing efficiency data from cells depleted for nonsense-mediated decay effectors, we show that introns located at the edge of nucleosomes display higher splicing efficiency than those at the center. However, multiple regression analysis indicates that the low GC content of introns, rather than nucleosome positioning, is associated with high splicing efficiency. Our data reveal a complex link between GC content, nucleosome positioning, and intron evolution in Paramecium.

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Section: Discussionmentioning

confidence: 99%

GC content, but not nucleosome positioning, directly contributes to intron splicing efficiency in Paramecium

et al. 2022

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GC content but not nucleosome positioning directly contributes to intron-splicing efficiency in Paramecium

Gnan

Matelot

Weiman

et al. 2021

Preprint

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Eukaryotic genes are interrupted by introns that must be accurately spliced from mRNA precursors. With an average length of 25 nt, the >90,000 introns of Paramecium tetraurelia stand among the shortest introns reported in eukaryotes. The mechanisms specifying the correct recognition of these tiny introns remain poorly understood. Splicing can occur co-transcriptionally and it has been proposed that chromatin structure might influence splice site recognition. To investigate the roles of nucleosome positioning in intron recognition, we determined the nucleosome occupancy along the P. tetraurelia genome. We showed that P. tetraurelia displays a regular nucleosome array with a nucleosome repeat length of ∼151 bp, amongst the smallest periodicities reported. Our analysis revealed that introns are frequently associated with inter-nucleosomal DNA, pointing to an evolutionary constraint to locate introns at the AT-rich nucleosome edge sequences. Using accurate splicing efficiency data from cells depleted for the nonsense-mediated decay effectors, we showed that introns located at the edge of nucleosomes display higher splicing efficiency than those at the centre. However, multiple regression analysis indicated that the GC content, rather than nucleosome positioning, directly contributes to intron splicing efficiency. Our data reveal a complex link between GC content, nucleosome positioning and intron evolution in Paramecium.

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ProA and ProB repeat sequences shape genome organization, and enhancers open domains

Bonnet,

Hulo,

Mourad

et al. 2023

Preprint

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SUMMARYThere is a growing awareness that repeat sequences (RepSeq) - the main constituents of the human genome - are also prime players in its organization. Here we propose that the genome should be envisioned as a supersystem with three main subsystems, each composed of functionally redundant, cooperating elements. We define herein ProA and ProB RepSeqs as sequences that promote either the A/euchromatin or the B/heterochromatin compartment. ProA and ProB RepSeqs shape A/B partitioning, such that the relative proportions of ProA and ProB RepSeqs determine the propensity of a chromosome segment to adopt either an A or a B configuration. In human, core ProA RepSeqs are essentially made of Alu elements, whereas core ProB RepSeqs consist of young L1 and some Endogenous Retroviruses (ERVs) as well as a panel of AT-rich microsatellites and pericentromeric and telomeric satellites. Additionally, RepSeqs with more indefinite character and, importantly, their derivatives known as “transcriptional enhancers”, can shift between ProA and ProB functions and thus act to open or close specific chromatin domains depending on the cellular context. In this framework, genes and their promoters appear as a special class of RepSeqs that, in their active, transcribed state, reinforce the openness of their surroundings. Molecular mechanisms involve cooperativity between ProB elements, presumably underpinned by the condensate-like properties of heterochromatin, which ProA elements oppose in several ways. We provide strong arguments that altered CpG methylation patterns in cancer including a marked loss in the B compartment, result primarily from a global imbalance in the process of CpG methylation and its erasure. Our results suggest that the resulting altered methylation and impaired function of ProB RepSeqs globally weaken the B compartment, rendering it more plastic, which in turn may confer fate plasticity to the cancer cell.

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Coupling Between Sequence-Mediated Nucleosome Organization and Genome Evolution

Cited by 5 publications

References 0 publications

GC content, but not nucleosome positioning, directly contributes to intron splicing efficiency in Paramecium

GC content, but not nucleosome positioning, directly contributes to intron splicing efficiency in Paramecium

GC content but not nucleosome positioning directly contributes to intron-splicing efficiency in Paramecium

ProA and ProB repeat sequences shape genome organization, and enhancers open domains

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