UNC Study Reveals How 3 Molecules Drive Gene-Silencing Condensates

Researchers uncover a self-clustering mechanism in the Polycomb protein CBX2 that is essential for initiating the formation of gene-repressive condensates.

Published on Mar. 5, 2026

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A new study from the University of North Carolina at Charlotte has uncovered how an exceptionally scarce protein, CBX2, can orchestrate the assembly of large-scale gene-silencing structures inside cells. The findings, published in Molecular Cell, identify a self-clustering mechanism in CBX2 that is essential for initiating the formation of gene-repressive condensates and guiding stem cells toward their proper fates.

Why it matters

Polycomb complexes are essential for establishing and maintaining cell identity, yet the physical principles behind their repression have remained elusive. This study provides new insights into how low-abundance proteins like CBX2 can have an outsized influence in shaping the epigenome and regulating cell fate decisions. Understanding the mechanisms behind Polycomb condensate formation is crucial for understanding developmental disorders and cancers linked to Polycomb dysfunction.

The details

Using ultra-sensitive single-molecule imaging and genetic engineering, the researchers discovered that condensates in mouse embryonic stem cells form around an unexpectedly small core: just three molecules of the protein CBX2. Despite its scarcity, CBX2 proved essential for organizing and positioning the hallmark histone modification H3K27me3, impacting gene repression. As cells differentiate, the condensates change, with neural progenitor cells containing roughly 15 CBX2 molecules per condensate, five times as many as in embryonic stem cells.

  • The study was published on March 5, 2026.

The players

Xiaojun Ren

UNC Charlotte Associate Professor and Irwin Belk Distinguished Scholar of Biology, who led the research team.

Polycomb complexes

Essential protein complexes for establishing and maintaining cell identity.

CBX2

A Polycomb protein that can dictate the assembly of large regulatory structures and act as a seed for the entire condensate, despite being one of the least abundant Polycomb proteins in stem cells.

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What they’re saying

“This is remarkable. CBX2 is one of the least abundant Polycomb proteins in stem cells, yet it can dictate the assembly of these large regulatory structures and act as a seed for the entire condensate.”

— Xiaojun Ren, UNC Charlotte Associate Professor and Irwin Belk Distinguished Scholar of Biology (Molecular Cell)

“Without CBX2's ability to self-cluster, the cells simply cannot execute their developmental programs. Just as a raindrop needs a tiny speck of dust to form in a humid sky, these three molecules act as the 'seeds' that pull the cell's Polycomb proteins together into a functional droplet.”

— Xiaojun Ren, UNC Charlotte Associate Professor and Irwin Belk Distinguished Scholar of Biology (Molecular Cell)

What’s next

The researchers plan to further investigate the role of CBX2 and Polycomb condensates in cell fate determination and developmental disorders.

The takeaway

This study challenges the long-standing assumption about how Polycomb condensates form, revealing that a small number of CBX2 molecules can act as 'seeds' to initiate the assembly of large-scale gene-silencing structures. This new model provides important insights into the mechanisms behind epigenetic regulation and cell identity.