How clusters of active molecules boost gene expression during development

During the early development of embryos, the sudden activation of thousands of genes marks a crucial stage. New research reveals how stable groups of molecules called RNA polymerase II associate with active genes to regulate their expression. These clusters are not fixed structures, but dynamic assemblies that evolve with transcriptional activity.

Scientists have observed that, in the fruit fly, these clusters form as early as the first cell divisions. Initially, they mainly contain molecules in the transcription initiation phase. Then, as gene activity intensifies, the clusters change in composition and predominantly house molecules in the elongation phase. This transition coincides with an increase in messenger RNA production, showing that the lifespan and intensity of the clusters are directly linked to the efficiency of transcription.

By specifically blocking the initiation or elongation of transcription, researchers confirmed that cluster formation depends on initiation, while their stability is influenced by elongation. When a gene activates, a single cluster persists throughout RNA production, and its intensity reflects the gene’s activity level. Thus, each active gene appears to be associated with its own cluster, rather than shared structures among multiple genes.

These findings shed light on a fundamental mechanism: RNA polymerase II clusters are not mere passive accumulations, but key players that optimize transcription by locally concentrating the necessary molecules. Their dynamics explain how cells finely tune gene expression according to their needs, without resorting to complex processes such as phase separation. This discovery opens avenues for understanding how nuclear organization influences genetic regulation.

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Official Reference

DOI: https://doi.org/10.1038/s41467-026-70775-8

Title: A single cluster of RNA Polymerase II molecules is stably associated with active genes

Journal: Nature Communications

Publisher: Springer Science and Business Media LLC

Authors: Apratim Mukherjee; Manya Kapoor; Kareena Shankta; Samantha Fallacaro; Raymond D. Carter; Gabriela Hayward-Lara; Puttachai Ratchasanmuang; Yara I. Haloush; Mustafa Mir