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Model predicts timing windows for partial cellular reprogramming via OSK(M) On 1 September Matteo Chiarki and Steffen Rudolph posted a theoretical preprint on bioRxiv. In a minimal model and computer simulations, transient activation of OSK(M) — proteins that alter gene activity — produces three distinct outcomes. Epigenetic marks that regulate genes remodel faster than the three‑dimensional packing of DNA in the model. Partial reprogramming should change age‑related gene‑expression signatures while preserving cell identity. The authors linked epigenetic marks to chromatin — DNA with proteins in the nucleus — noting that marks influence chromatin packing and that contacts between distant DNA regions help maintain a similar mark distribution. A short pulse nearly restores the original state; an intermediate duration makes the average mark balance sensitive to small perturbations at the boundary between stable states, while chromatin stays compact and retains long‑range contacts. After OSK(M) is switched off, this network restores mark correlations. A long pulse opens chromatin, reduces long‑range contacts, and erases correlational memory. The authors tested one model prediction using published mouse‑cell data. In embryonic fibroblasts, correlations of the repressive epigenetic mark H3K9me3 decayed more slowly in dense B‑compartments than in open A‑compartments; in embryonic stem cells with weaker chromatin compartmentalization the difference was smaller, qualitatively supporting the model’s link between chromatin compactness and correlation range. In their 2025 preprint Chiarki, Benjamin Simons and Rudolph described three timescales of methylation changes — fast molecular events, intermediate dynamics, and slow transitions — and the new work adds the three‑dimensional shape of chromatin to this framework. They propose measuring chromatin contacts and several epigenetic marks over time during OSK(M) induction. In the model, altering chromatin compactness or the feedback between mark reading and writing should shift the boundaries between the three regimes. 🔗 Read original →