TotipotentZygotChrom · Mechanisms of chromatin organization and reprogramming in totipotent mammalian zygotes

Totipotency, the developmental potential of a cell to give rise to all cell types, is naturally achieved when differentiated egg and sperm fuse to form the one-cell zygote. How chromatin is epigenetically reprogrammed to totipotency within hours after fertilisation remains a central question in biology. We aim to address this by investigating the mechanisms of reprogramming and the spatial reorganisation of chromatin in mammalian zygotes. Our interdisciplinary approach combines mechanistic cell biology with genetics and genomics to understand how chromatin reorganisation promotes totipotency and to identify key regulators of this process in zygotes. Molecular insights into reprogramming to totipotency are crucial to understand the essential zygotic stage of sexually reproducing species. A better understanding of how cells naturally reprogram chromatin to totipotency, a state upstream of pluripotency, has the potential to improve induced reprogramming technology and revolutionize regenerative medicine. Our aim is to understand how chromatin is reprogrammed to totipotency. To reach this ambitious goal: 1) We will discover new general concepts of genome organization, as well as reprogramming-specific aspects, by capitalising on our recently developed single-nucleus Hi-C method to dissect spatial reorganisation of chromatin in zygotes. We will investigate the relationship between chromatin reorganisation and transcription. 2) We will uncover mechanisms of zygotic reprogramming by elucidating the loci and factors that support active DNA demethylation during reprogramming of the paternal genome. 3) We will illuminate the origins and contributions of the oocyte since the factors responsible for reprogramming likely reside as proteins or RNA in the unfertilized egg. Overall, these studies will provide novel insights into how chromatin is reprogrammed and spatially reorganised towards a totipotent state that facilitates zygotic genome activation.