Heterogeneity as a feature: unraveling chromatin's role in nuclear mechanics.

Mechanical forces are a ubiquitous feature of the cellular environment. These forces propagate to the nucleus, where the mechanical response is critical for cellular function and survival. In addition to the nuclear lamina and cytoskeletal connections, chromatin is a key structural and mechanoresponsive element which not only contributes to bulk stiffness but also dynamically adapts its organization in response to mechanical stress. Crucially, chromatin is not a uniform material - its organization and mechanical properties vary across time, cell state, and even within individual nuclei. This heterogeneity underpins compartmentalization, gene regulation, and potentially, disease states when disrupted. In this review, we summarize recent experimental advances that have illuminated chromatin's role in nuclear mechanics, emphasizing the importance of heterogeneity. We argue that an integrated, multiscale, and quantitative framework is essential for dissecting chromatin's mechanical contributions. By doing so, the field will be better positioned to link nuclear mechanics to functional biological outcomes.