A minimal G$\bar{\textrm{o}}$-model for rebuilding whole genome structures from haploid single-cell Hi-C data

Abstract

We present a minimal computational model, which allows very fast, on-the-fly construction of three dimensional haploid interphase genomes from single cell Hi-C contact maps using the HOOMD-blue molecular dynamics package on graphics processing units. Chromosomes are represented by a string of connected beads, each of which corresponds to 100,000 base pairs, and contacts are mediated via a structure-based harmonic potential. We suggest and test two minimization protocols which consistently fold into conformationally similar low energy states. The latter are similar to previously published structures but are calculated in a fraction of the time. We find evidence that mere fulfillment of contact maps is insufficient to create experimentally relevant structures. Particularly, an excluded volume term is required in our model to induce the formation of chromosome territories. We also observe empirically that contact maps do not capture the chirality of the underlying structures. Depending on starting configurations and protocol details, one of two mirror images emerges. Finally, we analyze the occurrence of knots in a particular chromosome. The same knot appears in (almost) all structures irrespective of minimization protocols or even details of underlying potentials providing further evidence for the existence of knots in interphase chromatin.