Illuminating radial genome organization in the nucleus

In exciting preliminary experiments leveraging our GPSeq method we discovered that the genome of mammalian cells in interphase folds into a steep radial gradient of guanine and cytosine (GC) density, which seems to persist at the level of individual mitotic chromosomes.

However, we still lack a fundamental understanding of how this higher-order 3D genome architecture is established and what its functional implications are.

Here, I go beyond the state-of-the-art and propose that the observed steep radial GC-gradient is a universal design principle of the radial arrangement of the genome in the nucleuswhich I call the radiality principlethat provides a biophysical framework for spatially orchestrating key nuclear processes, beyond gene expression regulation.

To test this hypothesis, in this project I pursue five Objectives: (1) First, we develop a novel approach (GP-C) for high-resolution single-cell 3D genome reconstructions to study whether the radial GC-gradient is indeed a universal property of nuclei across different species and cell types. (2) Next, we apply GP-C together with RNA-seq to monitor genome radiality and concurrent gene expression changes as cells undergo karyotype rewiring or significant epigenetic perturbations. (3) In parallel, we develop innovative approaches to probe the internal structure of mitotic chromosomes and model how genome radiality is reorganized as cells traverse mitosis. (4) We then expand our preliminary finding of large-scale DNA-RNA contact hubs that seem to shape cell-type specific radiality landscapes by opposing the radial GC-gradient. (5) Finally, we pioneer methods for profiling nuclear proteins radially and apply them to test the bold hypothesis that the radiality principle provides a blueprint for organizing numerous nuclear processes.

This project aims at conclusively addressing long-standing questions in the field of 3D genome biology and proposes novel mechanisms of nuclear function regulation.