Mitochondrial stress signaling shapes the nuclear response to loss of the chromatin reader MRG-1

Perinuclear sequestration of heterochromatin is a major conserved feature of nuclear architecture. In Caenorhabditis elegans, the euchromatic reader MRG-1 was previously shown to promote peripheral localization of heterochromatin through an indirect mechanism that remained largely unknown. Here, we show that loss of MRG-1 activates a mitochondrial stress response. Genetic ablation of the PMK-3/MAPK mitochondrial stress regulator CBP-3 reveals that this pathway contributes to both detachment of a heterochromatic reporter from the nuclear periphery and approximately one-third of the transcriptional changes induced by mrg-1 depletion. Strikingly, loss of cbp-3 in MRG-1-deficient animals exacerbates mitochondrial dysfunction, fertility defects and embryonic lethality, indicating that part of the nuclear response induced by MRG-1 loss contributes to adaptation to mitochondrial stress rather than constituting a defect in heterochromatin 3D organization as previously thought. Together, our findings identify mitochondrial stress signaling as an unexpected mediator of the nuclear response to MRG-1 loss, demonstrating its contribution to gene regulation while supporting the idea that stress-induced changes in cellular physiology can also shape nuclear organization.