Folded in Two: Liver Cells Lose a Hidden X Chromosome Shape on the Road to Cancer

In a discovery that reframes how scientists think about the earliest steps of liver cancer, researchers have mapped the four-dimensional architecture of the genome in healthy and diseased livers and found that the active X chromosome undergoes a dramatic structural collapse during tumor development. The study, published in Nature Cell Biology, reveals that in normal liver tissue the active X chromosome adopts a distinctive two-part, or bipartite, mega-domain organization that has never before been described in an active chromosome. As liver disease progresses from fibrosis to cirrhosis and ultimately hepatocellular carcinoma, this bipartite structure dissolves, the two halves of the chromosome merge, and a wave of X-linked gene activation follows—changes that appear to actively push liver cells toward a premalignant state, particularly in males.

The research, led by Xiaoli Xie, Delin Tan, Jingyun Mo and colleagues under the supervision of Huiqing Jiang, Tingting Li and Jia Wang, set out to address a conspicuous gap in cancer genomics. While alterations in three-dimensional chromosome organization—topologically associating domains, chromatin loops and A/B compartments—are well documented in many tumors, the behavior of the X chromosome itself during carcinogenesis has attracted remarkably little attention. Yet the X chromosome carries more than 800 genes, many involved in cell proliferation, metabolism and immune regulation, and liver disease is notorious for its pronounced sex bias: men face a substantially higher risk of hepatocellular carcinoma than women, a pattern the team suspected might be written into the architecture of the sex chromosomes.

To follow genomic architecture across disease progression, the researchers built what they describe as a 4D nucleome landscape, combining chromosome conformation capture technologies such as Hi-C with ChIP-seq, RNA-seq, whole-genome sequencing and DNA methylation profiling, sampled at multiple time points as chemically induced liver disease unfolded in mice. Using F1 hybrid mice, in which the two parental X chromosomes can be distinguished by allele-specific sequence variants, the team could separate the folding of the single active X chromosome in males from the paired active and inactive X chromosomes in females. This allelic resolution proved critical, because it exposed a striking asymmetry: the conformational changes and gene activation occurring on the male active X chromosome during hepatocarcinogenesis were far more pronounced than those on the female active X chromosome, mirroring the male bias seen in human liver disease.

The most surprising finding emerged when the team turned to human hepatic tissue. In normal liver samples from both men and women, the active X chromosome is not organized as a single continuous domain but is split into two large mega-domains separated by a defined boundary located near the 90-megabase region of the chromosome. This bipartite configuration is specific to the liver—it was not observed in other tissues such as colon and lung—and, notably, it appears largely independent of the polyploid state of hepatocytes, which commonly carry doubled or quadrupled genome copies without ill effect. The bipartite active X chromosome, in other words, is a liver-specific architectural feature, maintained even in cells with unusual ploidy.

That stability, however, collapses early in disease. Analyzing fibrotic, cirrhotic and tumoral liver tissue from patients of both sexes, the researchers found that the mega-domain boundary weakens and the two halves of the active X chromosome merge into a single, unified domain. The merging is not merely a passive byproduct of genomic chaos in tumors. When the two halves fuse, the strengthened long-range contacts between them occur predominantly between A-type, active compartments, and these new A–A interactions are associated with the activation of X-linked genes. Genes on the X chromosome were among the most disproportionately upregulated in hepatocellular carcinoma samples, a pattern confirmed in data from The Cancer Genome Atlas, where the ratio of upregulated to total genes on the X chromosome ranked at or near the top in male tumors.

To establish causality rather than correlation, the team employed CRISPR–Cas3, a genome-editing system capable of deleting megabase-scale stretches of DNA that standard Cas9 cannot handle. By excising the boundary element that separates the two mega-domains of the active X chromosome, the researchers recreated, in isolation, the architectural event that accompanies liver cancer. The result was unambiguous: disruption of the bipartite conformation alone was sufficient to trigger a premalignant transition. In liver organoids, boundary deletion transformed normally cystic structures into thickened, compact spheroids reminiscent of early tumor growth, accompanied by the activation of X-linked genes. The boundary, it seems, functions as a tumor-suppressive architectural element whose loss unlocks oncogenic expression programs.

Having demonstrated that structural dissolution drives malignant change, the researchers then asked which of the activated X-linked genes actually matter for liver cancer. Using complementary CRISPR-based screening approaches—CRISPRa to boost the expression of genes that were weakly expressed, and CRISPRi to silence genes that were highly expressed—the team winnowed the long list of upregulated X-linked genes down to a set of functional drivers in hepatocellular carcinoma, including metabolic and stress-response genes such as G6PD and members of the ARMCX family. The identification of these effective genes provides a bridge between an abstract chromosomal conformation and concrete molecular targets that could, in principle, be therapeutically interrogated.

The study’s technical scope is considerable. The raw data, encompassing Hi-C, ChIP-seq, RNA-seq, whole-genome sequencing and bisulfite sequencing from both mouse and human samples, have been deposited in public archives, and all analysis code has been released through GitHub and Zenodo. Genome-wide, the researchers also documented the broader erosion of liver genome organization during carcinogenesis: topologically associating domains weakened, CTCF and H3K27ac signals at boundaries diminished, chromatin loops faded, and DNA methylation increased. Against this backdrop of global architectural decay, the specific, boundary-dependent dissolution of the bipartite active X chromosome stands out as an unusually discrete and mechanistically tractable event—one of the earliest and most consistent architectural signatures of hepatocarcinogenesis in both mice and humans.

The findings also carry implications for the long-standing puzzle of sex bias in liver cancer. Because males possess only a single X chromosome, every hepatocyte depends entirely on the architectural integrity of that one active X for proper dosage regulation of X-linked genes. The more pronounced conformational disruption and gene activation observed on the male X during disease progression offers a structural explanation for why male livers appear more vulnerable to malignant transformation, complementing earlier hypotheses about tumor-suppressor genes that escape X inactivation. Intriguingly, the work resonates with prior studies showing that the inactive X chromosome also folds into a bipartite structure in mice—one organized around the macroH2A-rich DXZ4-like boundary—suggesting that bipartite architecture may be a general feature of X chromosome biology whose functions differ profoundly between the active and inactive states.

For the field of cancer genomics, the message is that the fourth dimension of the genome—its behavior across time and disease states—can reveal vulnerabilities invisible to static snapshots. A liver-specific, megabase-scale boundary on the active X chromosome emerges from this study as both an early casualty of hepatocarcinogenesis and a functional guardian against it. If confirmed and extended, monitoring the integrity of this bipartite structure, or the X-linked genes it restrains, could eventually inform risk stratification in patients with chronic liver disease, while the boundary itself and the genes it controls offer fresh mechanistic entry points into one of the world’s deadliest cancers.

Subject of Research: Dissolution of the bipartite active X chromosome structure during hepatocellular carcinoma development

Article Title: 4D nucleome landscape reveals dissolution of bipartite active X chromosome in liver cancer development

Article References: 4D nucleome landscape reveals dissolution of bipartite active X chromosome in liver cancer development. (n.d.). https://doi.org/10.1038/s41556-026-02063-y

Image Credits: AI Generated

DOI: 10.1038/s41556-026-02063-y

Keywords: X chromosome, 4D nucleome, hepatocellular carcinoma, genome architecture, Hi-C, bipartite mega-domain, liver fibrosis, CRISPR-Cas3, X-linked gene activation, sex bias in cancer, chromatin loops, premalignant transformation