Recording cellular memory to unveil the mechanism of brain memory

Cell identity and states are dictated by gene expression programs, influenced by a range of epigenetic modalities. In the neuronal system, these mechanisms underlie various functions, such as maturation and memory formation, and their deficits are linked to various neurological disorders. Recent advancement of single-cell sequencing technologies, including scRNA-seq, has accelerated our understanding of the cellular diversity with respect to molecular profiles. However, existing high-throughput sequencing methods have an inherent limitation that they can primarily provide a static ‘snapshot’ of molecular states due to the need to lyse cells for nucleic acid extraction, posing a barrier in analyzing cell fate-decision dynamics. Thus, a novel technology for whole-genome history tracing, namely multi-timepoints observation, represents a significant innovation.Here, we report a novel ‘time-machine ’-like technology for retrospectively tracing the history of epigenetic and transcriptional changes at specific past time points in postmitotic neurons, a concept for which we have recently established a proof of principle. This will enable the analysis of multimodal epigenetic and transcriptional dynamics of over 10,000 genes, as well as more than 100,000 regulatory elements during neuronal fate decisions. We are applying this technology to reveal how heterogeneous subpopulations of memory-encoding engram cells emerge in the mouse brain, with a special focus on their excitability in memory encoding and recall events. Through this approach, we will address the molecular mechanisms of how a subpopulation of neurons becomes functionally relevant in memory formation.