Multiscale Modeling Primer: Focus on Chromatin and Epigenetics

Essential life processes take place across multiple space and time scales in living organisms but understanding their mechanistic interactions remains an ongoing challenge. Advanced multiscale modeling techniques are providing new opportunities and insights into these complex processes. In cells, meters of chromatin are folded into a nucleus with a diameter on the order of microns. The three-dimensional chromatin structure coupled with biochemical processes that turn genes on or off, specify a given cell type through a complicated set of interactions collectively referred to as epigenetics. Important epigenetic processes include the differential accessibility of genomic loci to transcription factors and chemical modifications to DNA and DNA-binding molecules such as histones. The dynamics of these epigenetic processes span timescales from milliseconds to years. How do chemical modifications consisting of a handful of atoms cooperate to modulate genome folding at the scale of the nucleus and impact organism outcomes? In this review, we highlight the inherently multiscale nature of chromatin organization, with a focus on computational modeling to bridge the gaps in our understanding of biochemical processes across scales. We review relevant chromatin biology, including major types of epigenetic modifications as well as the higher order chromatin structures to present a multiscale view of chromatin. We also review relevant computational methods to simulate chromatin structure, function, and dynamics, as well as experimental techniques that inform and validate said models. Finally, we argue that multiscale modeling provides a path forward towards understanding emergent behavior in this inherently multiscale system.