Retrospective and multifactorial single-cell profiling reveals sequential chromatin reorganization during X inactivation.

The regulation of gene expression is governed at multiple levels of chromatin organization. However, how gene regulation is co-ordinated remains relatively unexplored. Here we develop Dam&ChIC, a method that enables retrospective and multifactorial chromatin profiling in single cells. Dam&ChIC employs chromatin labelling in living cells with (m6)A to acquire a past chromatin state, coupled with an antibody-mediated readout to capture the present chromatin state. Analyses of diverse factor combinations highlight its versatility and superior resolution. By tracking lamina-associated domain inheritance over the cell cycle, we showcase that Dam&ChIC provides retrospective single-cell chromatin data. When applied in random X chromosome inactivation, Dam&ChIC disentangles the temporal order of chromatin remodelling events. Upon mitotic exit and following Xist expression, the inactive X chromosome undergoes extensive genome-lamina detachment, preceding spreading of Polycomb. We anticipate that Dam&ChIC will be instrumental in unravelling the interconnectivity and order of gene-regulatory events underlying cell-state changes during development.