The research, led by Martin Grundy, Claire Seedhouse and Daniel Booth at the University of Nottingham, focuses on a structure that has long fascinated cell biologists but remained poorly connected to human disease: the mitotic chromosome periphery, or MCP. This is a thin but elaborate layer of proteins and RNA that coats the surface of condensing chromosomes during mitosis. Far from being decorative, the MCP acts as a temporary staging ground for nucleolar components, the machinery that builds ribosomes, which are dismantled when the nucleolus disassembles at the start of cell division. By tethering these factors to chromosome surfaces, the cell ensures they are positioned to reassemble nucleoli rapidly in the newborn daughter nuclei. The Nottingham team set out to map this compartment in unprecedented detail and to ask what happens when a notorious leukaemia mutation interferes with it.

Using a proteomic strategy that captures proteins operating in close physical proximity to Ki-67, the best-characterised scaffold protein of the chromosome periphery, the researchers defined a mitosis-specific Ki-67 interactome. This inventory not only confirmed known residents of the MCP but also identified additional components, expanding the catalogue of factors that crowd around dividing chromosomes. When the team cross-referenced the genes encoding these components against cancer mutation databases, a striking pattern emerged: MCP genes are commonly mutated across tumour types, and among them was nucleophosmin, or NPM1, a protein with a central role in nucleolar structure and function. That observation reframed the chromosome periphery as more than a curiosity of cell division; it positioned it as a compartment whose disruption could plausibly contribute to malignancy.

The significance of NPM1 in this context is hard to overstate. Mutations in the NPM1 gene are the most frequent genetic alteration in acute myeloid leukaemia, an aggressive cancer of the blood-forming tissue that predominantly affects older adults. The leukaemia-specific mutations, collectively termed NPM1c+, insert a short stretch of amino acids that creates a new export signal, driving the protein out of the nucleus and into the cytoplasm. Under the microscope, this mislocalisation is a diagnostic hallmark: instead of staining the nucleoli, NPM1 lights up the cytoplasm of the leukaemic blasts. Clinicians use this cytoplasmic pattern to identify a distinct subclass of AML, one that generally responds well to certain treatments but carries its own risks of relapse. What has remained murky is exactly how the mutant protein sustains its exile from the nucleus across the generations of dividing cells.

Grundy and colleagues demonstrate that the answer lies partly in mitosis itself. They found that NPM1c+ fails to bind adequately to the mitotic chromosome periphery, the very platform that wild-type NPM1 uses to stay anchored near the reforming nuclei. Instead, the mutant protein forms aggregates during cell division, drifting away from the chromosomes and thereby losing its ticket back into the nucleolus when division completes. Live-cell imaging and complementary biochemical assays showed that this failure of MCP loading is not a minor side effect; it represents a genuine mechanistic defect that compounds the export-signal problem created by the mutation. In other words, the mutant protein is not merely evicted from the nucleus once; it is repeatedly denied re-entry every time the cell divides.

The study also uncovered a second, subtler contributor to the mislocalisation puzzle. At the onset of mitosis, the nuclear envelope breaks down and the cell undergoes what the authors describe as de-compartmentalisation: the abrupt mixing of nuclear and cytoplasmic contents that accompanies the loss of the nucleus as a separate compartment. The researchers showed that this mixing allows the formation of multimers containing both wild-type and mutant NPM1, complexes in which the mutant protein can effectively drag its normal counterpart along. These mixed assemblies further hinder the return of NPM1 to the nucleoli of daughter cells, meaning that even cells carrying a single mutant allele can experience a measurable depletion of functional nucleolar NPM1. The finding adds an important layer to the picture: mislocalisation is not a static property of the mutant protein but a dynamic process that exploits the normal chaos of cell division.

To test whether the chromosome periphery could be pushed to work harder, the team increased the expression of Ki-67, effectively enlarging the loading capacity of the MCP scaffold. The result was telling. With more Ki-67 available, a greater fraction of NPM1c+ became tethered to the chromosome periphery during mitosis, and the yield of nucleolar NPM1c+ in the daughter cells rose accordingly. This experiment demonstrates that the mislocalisation of the mutant protein is not an all-or-nothing state but a balance of competing forces, one that can be tipped by modulating the capacity of the chromosome periphery. It also raises the provocative possibility that the MCP, long regarded as a transient and inaccessible structure, could be a legitimate drug target in leukaemia.

The clinical dimension of the study came from an analysis of AML patient data, which revealed a significant interaction between Ki-67 expression levels and NPM1 mutation status in predicting overall survival. Among patients whose leukaemia carried wild-type NPM1, higher Ki-67 expression was associated with an increased hazard of death, consistent with the notion that rapidly cycling cells depend heavily on this mitotic scaffold. Among patients with the NPM1c+ mutation, however, the relationship inverted: higher Ki-67 was associated with a reduced hazard. The authors interpret this in light of their mechanistic findings, suggesting that in mutant cells, greater Ki-67-driven loading of NPM1c+ onto the chromosome periphery may partially restore nucleolar re-entry and, in doing so, temper some of the consequences of mislocalisation. Whatever the precise mechanism, the survival analysis underscores that the chromosome periphery is not merely a laboratory phenomenon but a factor with measurable prognostic weight in a major human cancer.

These findings arrive at a moment of genuine momentum in AML research. Over the past decade, the field has moved from one-size-fits-all chemotherapy towards targeted agents, including inhibitors of mutant IDH enzymes and the liposomal formulation of cytarabine and daunorubicin, yet relapse remains a stubborn problem, and the molecular events that sustain the leukaemic state inside dividing cells are still being mapped. The Nottingham study contributes a piece of that map that is genuinely new: it connects a mitotic structure to one of the defining molecular lesions of the disease, and it does so with a combination of proteomics, live imaging, perturbation experiments and patient survival data that gives the story both mechanistic depth and clinical texture. The work was supported by funding from the Biotechnology and Biological Sciences Research Council, the Royal Society, the Academy of Medical Sciences, the Leverhulme Trust, the Nottinghamshire Leukaemia Appeal and Nottingham Hospitals Charity.

There are, of course, caveats and open questions. The chromosome periphery exists only during the brief window of mitosis, which makes pharmacological intervention conceptually challenging, and the study’s mechanistic experiments were performed largely in cell models whose behaviour may not fully recapitulate the bone marrow environment of a patient. The prognostic interaction between Ki-67 and NPM1 status will need validation in larger, independent cohorts before it can inform clinical decision-making. Yet the conceptual payoff is substantial. The study shows that cancer-relevant phenotypes can arise not only from mutations in genes that regulate growth and survival, but from the failure of mutated proteins to navigate the physical reorganisation of the cell during division. It suggests that the mitotic chromosome periphery, with Ki-67 at its heart, represents an untapped therapeutic surface, and it offers leukaemia researchers a new question to pursue: not just what a mutant protein does in the resting cell, but what happens to it when the cell divides.

Subject of Research: Mechanisms of nucleophosmin mislocalisation during mitosis in acute myeloid leukaemia

Article Title: Ki-67, the chromosome periphery and de-compartmentalisation each contribute to nucleophosmin mislocalisation in acute myeloid leukaemia

Article References: Grundy, M., Woodmancy, P., Lucken, K., Xing, X., Markus, R., Bagia, S., Storr, S., Seedhouse, C. H., & Booth, D. G. (2026). Ki-67, the chromosome periphery and de-compartmentalisation each contribute to nucleophosmin mislocalisation in acute myeloid leukaemia. Nature Communications. https://doi.org/10.1038/s41467-026-78560-3

Image Credits: AI Generated

DOI: 10.1038/s41467-026-78560-3

Keywords: acute myeloid leukaemia, nucleophosmin, NPM1c+, Ki-67, mitotic chromosome periphery, mitosis, nucleolus, de-compartmentalisation, protein mislocalisation, cancer mutations, prognosis, cell division

A study published on September 22 in the journal Molecular Cell by researchers at The Ohio State University and the University of Zurich shows that linker histone H1 wanders aimlessly inside the cell even when its target, a nucleosome with spooled-up segments of DNA, is directly in front of it. Although H1 binds readily to two DNA strands that stick out from the nucleosome, it struggles to bind to the nucleosome itself. Only when a chaperone protein escorts it does H1 successfully load onto the nucleosome and carry out its gene-silencing role. The finding fills a long-standing gap in scientists’ understanding of how one of the genome’s most important architectural proteins finds its proper place.

The research team, led by first author Ehsan Akbari, a research scientist in the laboratory of senior author Michael Poirier, professor of physics at The Ohio State University, tackled the question with single-molecule experiments. Rather than averaging the behavior of millions of molecules together, single-molecule methods allow researchers to quantify molecular motions and interactions one molecule at a time, watching individual H1 proteins and their nucleosome targets before, during and after H1 bound to the DNA and to the center of the nucleosome. The team combined optical tweezer instrumentation, which uses highly focused laser light to manipulate and measure single molecules, with single-molecule fluorescence measurements to visualize the process in real time.

“Many proteins are dynamic, and the way you get at mechanistic dynamic information is by doing these single-molecule studies where you literally can watch in real time what individual molecules are doing,” Poirier said. This approach proved essential for a protein whose behavior defied expectations. When the researchers observed H1 in action, they found that the protein continues to move around even after it binds to DNA. More strikingly, instead of loading onto the nucleosome by way of the DNA it had attached to, the protein reflects away from the nucleosome entirely.

“It moves around and doesn’t even go to the nucleosome, which I didn’t believe,” Poirier said. That unexpected observation prompted the team to hypothesize that a chaperone protein might be the missing link in the loading process. Chaperone proteins are known to assist other proteins in folding, targeting and assembly, and three linker histone chaperone proteins were already known to science. When the researchers added these chaperones to their experiments, the results were dramatic.

“Amazingly, the chaperones did a bunch of things to regulate how H1 goes around and how it actually finds and gets onto nucleosomes. And that’s the main point, that people have not understood how H1 loads and gets onto a nucleosome,” Poirier said. “What we found was that it actually will directly load and likes to slide along DNA – we also didn’t even know that it would do that – but it needs a chaperone to help get onto the actual nucleosome.” The experiments revealed that H1 can load directly onto DNA and slide along it, a previously unknown behavior, but the final step of binding to the nucleosome core requires chaperone assistance.

The biological stakes of this process are considerable. Every cell in a plant, animal or human contains the organism’s entire genome, and nucleosomes fold in on each other, clumping together to form chromatin. Linker histone H1’s job is to facilitate chromatin compaction, ensuring that DNA segments containing genes the cell is not using stay wrapped up and unavailable for expression. “We know that H1 is important for compacting the genome, which is important for regulating gene expression,” Poirier said. “In the genome, regions that are going to be compacted are loaded with a lot of H1, while regions that are more open are going to have less H1.”

Most genes in any given cell are turned off at any moment, because only a small fraction of the genome is active in a particular cell type. Maintaining the silent majority in compacted states is therefore a fundamental requirement of cellular life, and H1 is a central player in that maintenance. “H1 is a key regulator of which genes are being used by a cell and which genes are not,” Poirier said. “If you want to understand how disease develops because gene expression is no longer working properly, then you need to understand how H1 works. Once you understand this, then you open up the possibility for new therapies that counteract this cause of disease.”

The connection to disease is not hypothetical. H1 is well known for its role in compacting genes and for its connection to cancer when it undergoes mutation. Mutations in linker histone genes and alterations in how H1 is deployed across the genome can disrupt the careful balance between open, active chromatin and closed, silent chromatin, contributing to the misregulated gene expression that characterizes cancer cells. Understanding the mechanics of how H1 reaches nucleosomes in the first place gives researchers a new handle on where this process could go wrong.

Though the work does not tell the entire H1 story, the step-by-step visualizations offer concrete directions for future research. Poirier’s laboratory has previously studied H1 variants and the post-translational modifications that can change H1 targeting and function after the protein has been fabricated by the cell. “One very natural thing to do next is to look at how these variants, post-translational modifications, and, most importantly, cancer-relevant mutations influence H1 properties and function that we are now in a position to measure,” he said. With single-molecule tools now capable of watching H1’s loading pathway in detail, the effects of disease-linked alterations can be tested directly.

The study, titled “Linker histone H1.0 loads onto nucleosomes through multiple pathways that are facilitated by histone chaperones,” was funded by the National Institutes of Health and the U.S. National Science Foundation. In addition to Akbari and Poirier, the co-authors included Nathaniel Burge of Ohio State and Matti Valdimarsson, Aritra Chowdhury and Benjamin Schuler of the University of Zurich. Together, their findings reframe a seemingly simple question – how does a protein find its binding site? – into a multi-step journey involving DNA sliding, unexpected reflection away from targets, and an essential chaperone handoff, deepening the mechanistic picture of how cells keep their vast genomes organized and their genes properly silenced.

Subject of Research: How linker histone H1 is targeted to nucleosomes with the help of histone chaperone proteins

Article Title: Protein key to cells’ gene regulation needs a chaperone to do its job

Article References: Protein key to cells’ gene regulation needs a chaperone to do its job. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: linker histone H1, nucleosome, chromatin compaction, gene regulation, histone chaperones, single-molecule imaging, optical tweezers, epigenetics, cancer mutations, Molecular Cell, Ohio State University, DNA packaging