# Chromatin state switching in a polymer model with mark-conformation coupling

## TL;DR

This paper models chromatin as a polymer with coupled magnetic and conformational states, revealing a first-order phase transition that explains discrete chromatin state switching during cell differentiation.

## Contribution

It introduces a polymer-Potts model with mark-conformation coupling, demonstrating a first-order phase transition in chromatin-like systems using mean-field analysis.

## Key findings

- Phase transition is first-order with a large magnetization jump.
- Small changes in epigenetic factors can cause macroscopic chromatin state switches.
- Model explains discrete chromatin state changes observed in biological processes.

## Abstract

We investigate the phase transition properties of the polymer-Potts model, a chain composed of monomers with magnetic degrees of freedom, with the motivation to study the conformation and mark switching dynamics of chromatin. By the mean-field approximation, we find that the phase transition between the swollen-disordered state and the compact-ordered state is discrete; it is first-order as in the long-range Potts model, but with a significantly larger jump in magnetization (i.e., mark coherence) upon the ordering transition. The results imply how small changes in epigenetic writer concentrations can lead to a macroscopic switching of the chromatin state, suggesting a simple mechanism of discrete switching observed, for instance, in cell differentiation.