Phase-Separation Discovery Reveals How a Key Gene-Regulating Complex Assembles Itself

Inside every cell that makes up the human body, thousands of genes are switched on and off with extraordinary precision. Among the molecular machines responsible for this choreography is the non-specific lethal, or NSL, complex, a chromatin-modifying assembly that binds to the promoters of housekeeping genes and keeps their transcription running. These housekeeping genes encode the basic machinery every cell needs to survive, which means the NSL complex sits close to the foundation of cellular life itself. When its subunits malfunction, the consequences are severe: disrupted development, intellectual disability, and cancer have all been causally linked to defects in NSL complex components. Yet despite decades of work mapping its parts, one fundamental question has remained stubbornly open. How does this multi-protein machine actually put itself together inside the crowded, chaotic environment of the cell nucleus?

A new study published in the journal Cellular and Molecular Life Sciences offers a striking answer. A team of researchers led by Yulei Wang, Zuhao Liu, Yameng Wang, Zhiyu Xing and Meisheng Ma of the Department of Histology and Embryology at Tongji Medical College, Huazhong University of Science and Technology in Wuhan, China, reports that the assembly of the NSL complex is driven by liquid-liquid phase separation, a physical process increasingly recognized as a central organizing principle of the cell interior. At the heart of the discovery is KANSL1, the essential scaffolding subunit of the complex, which the researchers show can condense into droplet-like compartments that recruit the other components and enable the intact complex to form. The work, published as an open-access article, reframes the NSL complex not as a machine that snaps together through rigid lock-and-key contacts alone, but as one whose architecture emerges from the soft-matter physics of biomolecular condensates.

To appreciate the significance of the finding, it helps to understand what the NSL complex actually is. The complex comprises at least seven evolutionarily conserved subunits: KANSL1, KANSL2, KANSL3, WDR5, MCRS1, KAT8 and PHF20, along with two associated factors, OGT and HCF1. KAT8, also known as MOF, is the catalytic engine, a histone acetyltransferase that deposits acetyl groups on histone proteins, thereby loosening chromatin and permitting gene expression. KANSL1, by contrast, contributes no catalytic activity of its own, but it is indispensable. It holds the complex together structurally and regulates its function, and previous work had established that without KANSL1 the complex cannot maintain its integrity. What remained elusive was the molecular mechanism underlying this regulatory role, and that is precisely the gap the new study set out to fill.

The researchers’ attention focused on a specific segment of the KANSL1 protein: intrinsically disordered region 4, or IDR4, a stretch of amino acids spanning residues 733 to 857 near the protein’s C-terminal end. Intrinsically disordered regions are segments of proteins that do not fold into a fixed three-dimensional structure. Instead, they remain floppy and dynamic, a property long considered puzzling but now understood to be crucial for many regulatory functions. One of the most consequential of these functions is liquid-liquid phase separation, the process by which disordered, multivalent proteins coalesce, like oil droplets in water, into concentrated liquid compartments that exchange molecules with their surroundings. Membrane-less organelles such as nucleoli and stress granules form this way, and growing evidence implicates phase separation in the organization of chromatin and transcriptional machinery.

Demonstrating that KANSL1 undergoes phase separation required the team to show that the protein displays the characteristic behaviors of a liquid condensate. The study reports that KANSL1 undergoes liquid-liquid phase separation mediated by IDR4, meaning that this specific disordered segment is both necessary and sufficient to drive the condensation process. In the condensed state, KANSL1-rich droplets behave as spatial hubs. Rather than assembling through a sequence of pairwise protein-protein interactions at some random location in the nucleus, the complex appears to build itself inside these droplets, where the local concentration of components is dramatically elevated. This spatial assembly mechanism solves a practical problem for the cell: finding and correctly combining nine different subunits in the vast nuclear volume becomes far more efficient when one partner first creates a dedicated reaction vessel.

The functional consequences of this condensation are substantial. According to the study, IDR4-dependent phase separation promotes the recruitment of KANSL2 and KANSL3, two of the complex’s conserved subunits, enabling the assembly of the intact NSL complex. In other words, the droplets act as gathering points that draw in the remaining parts and allow the full machine to take shape. Critically, the researchers found that this phase separation is not merely a structural curiosity. It is essential for the histone acetyltransferase activity of the NSL complex, meaning that without the condensation event, KAT8 cannot efficiently carry out the chemical modification of histones that the complex exists to perform. The physical state of the scaffold directly controls the enzymatic output of the machine it supports.

That enzymatic output, in turn, feeds directly into gene regulation. The NSL complex binds preferentially to the promoters of housekeeping genes, and its acetylation of histones at those sites is a key determinant of their transcriptional activity. The new study demonstrates that KANSL1 phase separation is required for the transcriptional regulation of the complex’s target genes, closing the causal chain from a disordered protein segment, through condensate formation and complex assembly, to enzymatic activity, and finally to the expression levels of genes that sustain cellular life. It is a vivid illustration of what biophysicists have argued for years: that the physical organization of the nucleus, down to the mesoscale behavior of individual proteins, can be as important to gene control as the DNA sequence itself.

The researchers also connected their findings to cellular behavior, showing that KANSL1 phase separation governs the proliferation and migration of HeLa cells, a widely used laboratory cell line derived from cervical cancer tissue. This observation carries particular weight given the established links between NSL complex subunits and oncogenesis. If the phase-separated state of KANSL1 is required for the complex to function, then perturbing that state, whether by mutation, altered expression, or pharmacological interference, could in principle disrupt the transcriptional program that cancer cells rely upon. While the study does not claim a therapeutic application, it identifies a concrete biophysical mechanism that could be targeted in future work on cancers and developmental disorders involving NSL complex dysfunction.

The clinical resonance of KANSL1 extends beyond cancer. The gene encoding KANSL1 lies within the 17q21.31 region, and haploinsufficiency of KANSL1 is known to underlie a neurodevelopmental disorder characterized by intellectual disability and developmental delay, a condition closely associated with what is often called Koolen-de Vries syndrome. The new findings suggest a possible mechanistic lens through which such mutations might act: changes that compromise the phase-separation behavior of IDR4, or the disordered region’s ability to recruit partner subunits, could cripple complex assembly even when the protein is present. Testing that idea in patient-derived systems would be a natural next step, and the study’s identification of a specific residue range, 733 to 857, gives researchers a precise molecular handle for such experiments.

More broadly, the work adds to a rapidly expanding catalog of cellular processes organized by biomolecular condensates, and it does so in a domain where the stakes are especially high. Epigenetic regulators such as the NSL complex sit at the intersection of development, disease and basic cellular physiology, and understanding how they assemble has been a longstanding challenge. By showing that a scaffolding subunit can self-organize the assembly of an entire chromatin-modifying machine through phase separation, the study broadens the mechanistic understanding of how liquid-liquid phase separation contributes to multi-protein complex formation and epigenetic gene regulation. It also raises new questions that the field will now pursue: How is the condensation of KANSL1 regulated in time and space? Do disease mutations alter the material properties of the condensates? And can the droplets be modulated, safely and specifically, to treat the disorders that arise when this essential assembly line falters? For now, the study stands as a compelling demonstration that some of the cell’s most important molecular machines are built not on rigid frames, but on droplets of liquid protein.

Subject of Research: Liquid-liquid phase separation of KANSL1 in the assembly and function of the NSL chromatin-modifying complex

Article Title: KANSL1 condensates drive spatial assembly of NSL complex

Article References: Wang, Y., Liu, Z., Wang, Y., Xing, Z., & Ma, M. (2026). KANSL1 condensates drive spatial assembly of NSL complex. Cellular and Molecular Life Sciences. https://doi.org/10.1007/s00018-026-06453-1

Image Credits: AI Generated

DOI: 10.1007/s00018-026-06453-1

Keywords: KANSL1, NSL complex, liquid-liquid phase separation, chromatin, epigenetics, histone acetyltransferase, KAT8, intrinsically disordered regions, gene regulation, housekeeping genes, biomolecular condensates, transcription