The long noncoding RNA FOSIL shapes the dynamics of FOS induction

Endogenous FOSIL (LINC01220) is linked to sharper HRG-driven FOS induction kinetics, delaying onset and prolonging shutoff when FOSIL RNA is depleted.

• Why it matters: Immediate-early genes need rapid, transient, precisely tuned activation, but the mechanisms that set both onset and shutoff timing are unclear.
• What they did: The study depleted FOSIL RNA and used Capture Micro-C to assess chromatin insulation and compaction, then tracked locus movement to nuclear speckles and measured FOS transcription at single transcription active sites.
• The result: FOSIL depletion weakens the FOS–FOSIL chromatin boundary, alters speckle dynamics, blunts early speckle-proximal FOS transcription, and extends late firing; CRISPRa activation of the endogenous FOSIL promoter enhances speckle association and FOS induction.

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