T cells provide immunity against bacteria, viruses and cancers. Upon detecting cognate antigen, naive T cells differentiate into activated effector cells and long lived memory cells. Research has shown that knocking out proteins which deposit and remove epigenetic marks such as histone post translational modifications (PTMs) perturb T cell differentiation and function (1). Moreover, histone PTMs are hypothesised to regulate gene expression through changes in the spatial organisation of chromatin. Therefore, visualising the T cell nucleus would elucidate the distribution, clustering and co-localisations of histone modifications. Thus, we utilise direct stochastic optical reconstruction microscopy (dSTORM) to image single molecules down to a resolution of 20 nm.
Using dSTORM, we identified active histone mark H3K4me3 to be localised in the centre of the T cell nucleus, whilst repressive histone mark H3K27me3 was found towards the nuclear periphery. This indicates that genes that are active and repressed occupy separate parts of the nucleus; suggesting that movement between these different compartments may choreograph T cell differentiation. We also found that as naïve T cells differentiate into effector T cells H3K4me3 moves towards the periphery. Furthermore, the movement of H3K4me3 is hindered when we knockdown the methyltransferase KDM6B which removes H3K27me3. Thus, this suggests that the cross-talk between H3K4me3 and H3K27me3 allows for the proper positioning of chromatin architecture during T cell differentiation. Utilising dSTORM, we are interested in investigating how the spatial organisation of histone PTMs regulates T cell differentiation. Understanding what drives T cell differentiation would be crucial to designing T cell-based vaccines and immunotherapies.