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bioRxiv · 10.64898/2026.07.31.741674

An RPEL-based FRET sensor for G-actin

Fedoryshchak, R. O.·FONS, J. M.·RENSHAW, M. J.·Treisman, R.
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Abstract

Actin is critical for cell integrity and nuclear processes, but methods to visualise how environmental and intracellular signals affect cellular monomeric (G-) actin levels are lacking. We present the GASPs (G-actin sensing proteins), genetically encoded G-actin FRET sensors. Using cytoplasmic- and nuclear-localised GASPs, we show that in fibroblasts integrity of focal adhesions plays a critical role in maintaining low G-actin levels, and that cytoplasmic and nuclear G-actin levels increase at high cell densities and when spreading is restricted. Upon serum stimulation, it is depletion of the cytoplasmic G-actin pool that correlates with rapid nuclear accumulation of the MRTF transcription factors, whose subcellular localisation is controlled by G-actin. Stimuli that induce rapid increases or decreases in cytoplasmic G-actin level induce similar but slower changes in nuclear G-actin level, indicating that fluctuations in nuclear G-actin levels are largely subservient to cytoplasmic actin dynamics.

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Fedoryshchak, R. O., FONS, J. M., RENSHAW, M. J., Treisman, R.. 2026-08-03. An RPEL-based FRET sensor for G-actin. https://doi.org/10.64898/2026.07.31.741674

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