The Physics of Cellular Identity

All cells in our body share the same genetic material as they descend from a common ancestor, the embryonic stem cell. This means that a skin cell and a neuron are genetically identical and yet they perform widely different functions. The specialisation of cells into tissues is guided by "epigenetic" factors which can operate "beyond the genes" and allow the regulation of gene expression irrespectively of the underlying DNA sequence. Even though it is broadly accepted that epigenetic factors operate in concert with 3D chromosome folding to decide and maintain cellular fate, the underlying biophysical principles are far from fully understood. How are epigenetic factors first established along the genome? How do cells remember their fate after division? What are the mechanisms regulating the change in cell identity, e.g. during reprogramming or ageing? In this talk, I will review our recent efforts to come up with simple physical models for these complex biological questions and I will present some of our key results.