ALT Figure 1. (A) Classical gel electrophoresis experiments showing mono-, di-, tri-, tetra-, and further multinucleosome bands upon chromatin digestion. (B) The nucleosome repeat length (NRL) is defined as the genomic distance between the centres of two neighbouring nucleosomes.

ALT Figure 2. Nucleosome mapping using MNase-seq versus ATAC-seq. (A) In MNase-seq, nucleosomes in both open and tightly packed genomic regions are accessible to digestion. MNase preferentially cleaves DNA between nucleosomes and digests DNA until it encounters a histone octamer, which provides a footprint of nucleosome-protected DNA regions. (B) Bulk MNase-seq results in averaged maps across millions of cells, effectively capturing all possible nucleosome positioning configurations. (C) Single-cell MNase-seq (scMNase-seq) results in a noisier and sparser signal. The resulting footprints still represent nucleosome-protected regions, but not all nucleosomes are represented. (D) In ATAC-seq, open regions can be accessed by the enzyme Tn5 transposase, which can insert primers in regions free from the binding of nucleosomes and transcription factors (TFs). (E) For open chromatin regions, nucleosome maps can be obtained from ATAC-seq similar to MNase-seq. (F) Closed, tightly packed chromatin...

ALT Figure 5. Molecular mechanisms affecting nucleosome spacing. (A) Linker histones H1 and nonhistone chromatin proteins which compete with H1s and modulate nucleosome spacing through structural and electrostatic mechanisms. (B) Chromatin remodellers actively reposition nucleosomes following context-dependent rules. (C) Cell state-dependent chromatin boundaries formed by CTCF and other structural proteins, as well as associated recruitment of chromatin remodellers which space nucleosomes. (D) Gene activity associated with remodeller action and RNA polymerases transcribing through the nucleosomes, leading to smaller distances between nucleosomes in regulatory regions and gene bodies. (E) DNA sequence repeats of different types.

ALT Figure 6. Examples of NRL changes in biological systems. (A) Cell differentiation leads to NRL changes between different cell types, e.g. mouse dorsal root ganglia neurons (NRL ∼165 bp) versus cortical astrocytes (NRL ∼183 bp) [175]. Schematic cell shapes are adapted from an image created in BioRender (https://BioRender.com/89trj2t). (B) Paired normal versus tumour breast tissues show NRL shortening in cancer (figure adapted from [36] under the CC BY 4.0 licence (https://creativecommons.org/licenses/by/4.0/)). (C) Nucleosome positioning derived from cfDNA of human volunteers shows NRL increase with age (figure reprinted from [79] under the CC BY 4.0 licence (https://creativecommons.org/licenses/by/4.0/)).

ALT Figure 5 from Jacob et al, 2024. NRL shortening as a novel breast cancer marker. A–E) NRL values calculated for each individual sample from this study inside different types of genomic regions. A) Transcriptionally active A-compartments of chromatin annotated in breast cancer MCF-7 cells; B) Regions surrounding gene promoters. C Genomic regions around Alu repeats; D) Regions enriched with H1X linker histones in breast cancer T47D cells; E) Differentially methylated DNA regions annotated based on cell lines MCF-10A, MCF-7 and MDA-MB-231. Open squares—average NRL values for a given condition; horizontal lines—median values. The colours of the points are assigned per sample as in Fig. 3A. F) A scheme of the change of nucleosome compaction in breast cancer tissues. DNA (black) is wrapped around histone octamers (grey) in contact with linker histones (blue). MNase used in this study or apoptotic nucleases present in situ (orange) cut DNA not protected by nucleosomes and linker histones.

ALT The study design and small-scale nucleosome repositioning analysis. A Scheme of the study: paired tumour/normal breast tissues taken from breast cancer patients numbered P1–P4 were used to determine nucleosome positioning using MNase-seq and MNase-assisted histone H3 ChIP-seq (MNase-H3), complemented by whole-genome sequencing of cell-free DNA extracted from blood plasma from the same patients. The analysis of each sample was performed individually, without pooling. B Example genomic region (Chr 17: 7,855,262–7,592,516) enclosing gene TP53 and nucleosome occupancy maps for patient P3. Tracks top to bottom: normal tissue MNase-H3 and MNase-seq; tumour tissue MNase-H3 and MNase-seq; cfDNA in two replicates; UCSC Genome Browser track with ENCODE Factorbook TF motifs. Rectangles show regions containing common (brown), gained (green) and shifted nucleosomes (violet). The gained and shifted classifications are not mutually exclusive. C Fold enrichment of nucleosomes that were gained and lost

ALT Nucleosome repeat length shortening in cancer. A Frequencies of distances between dyads of DNA fragments protected from MNase digestion in paired normal and tumour breast tissue samples from patient P2. B Genome-wide NRL values calculated for each sample reported in this study. The difference of NRLs between normal and tumour tissues is statistically significant (p = 0.014, paired sample t test). Open squares—average values across all samples in a given condition; horizontal lines—median values for a given condition. The colours of the points corresponding to NRL values in N/T tissues are assigned per patient and per experiment type as follows: MNase-seq: patient P1 (black), P2 (red), P3 (blue), P4 (green); MNase-assisted H3 ChIP-seq: patient P1 (violet), P3 (brown), P4 (cyan). Panels A and B use DNA fragments of sizes 120–180 bp. C NRL in normal (grey violins) and tumour (beige violins) breast tissue calculated inside genomic regions enriched with 160–180 bp DNA fragments (“long nuc”)

ALT Effects of linker histones on nucleosome repositioning in breast cancer. A Correlation of GC content and H1 occupancy in 10-kb regions genome-wide. H1 variants H1.0, H1.2 and H1.5 preferentially bind AT-rich regions, while H1.4 and H1X have a higher affinity for GC-rich regions. B–D Averaged aggregate profiles of H1 occupancy around different types of DNA fragments protected from MNase digestion. These profiles were first calculated individually for each MNase-seq tumour tissue sample reported in this study, and then averaged across all patients. B Occupancy of H1 variants around nucleosome dyads calculated for different DNA fragment sizes. C H1 occupancy in the region [-50, 50] bp around nucleosome dyad calculated for different H1 variants as a function of DNA fragment size. D Average H1X occupancy in T47D breast cancer cell line calculated around DNA fragments of 160–180 bp in normal (black lines) and tumour breast tissues (red). E Average H1X occupancy profiles...

ALT NRL shortening as a novel breast cancer marker. A–E NRL values calculated for each individual sample from this study inside different types of genomic regions. A Transcriptionally active A-compartments of chromatin annotated in breast cancer MCF-7 cells; B Regions surrounding gene promoters. C Genomic regions around Alu repeats; D Regions enriched with H1X linker histones in breast cancer T47D cells; E Differentially methylated DNA regions annotated based on cell lines MCF-10A, MCF-7 and MDA-MB-231. Open squares—average NRL values for a given condition; horizontal lines—median values. The colours of the points are assigned per sample as in Fig. 3A. F A scheme of the global change of nucleosome compaction in breast cancer tissues. DNA (black) is wrapped around histone octamers (grey) in contact with linker histones (blue). MNase used in this study or apoptotic nucleases present in situ (orange) cut DNA not protected by nucleosomes and linker histones. Cancer cells have shorter NRL...