Multiscale 3D Genome Reorganization during Skeletal Muscle Stem Cell Lineage Progression and Muscle Aging

Abstract: 3D genome rewiring is known to influence spatiotemporal expression of lineage-specific genes and cell fate transition during stem cell differentiation and aging processes. Yet it is unknown how 3D architecture remodels and orchestrates transcriptional changes during skeletal muscle stem cell (also called satellite cell, SC) activation, proliferation and differentiation course. Here, using in situ Hi-C we comprehensively map the 3D genome topology reorganization at multiscale levels during mouse SC lineage progression and integrate with transcriptional and chromatin signatures to elucidate how 3D genome rewiring dictates gene expression program. Specifically, rewiring at compartment level is most pronounced when SC becomes activated. Striking loss in TAD border insulation and chromatin looping also occurs during early activation process. Meanwhile, TADs can also form TAD clusters and super-enhancer containing TAD clusters orchestrate stage-specific gene expression during SC early activation. Furthermore, we elucidate 3D chromatin regulation of key transcription factor, PAX7 and identify cis-regulatory elements that are crucial for local chromatin architecture and Pax7 expression. Lastly, 3D genome remodeling is profiled in SCs isolated from naturally aging mice, unveiling that geriatric SCs display a prominent gain in long-range contacts and loss of TAD border insulation. Genome compartmentalization and chromatin looping are evidently altered in aged SC while geriatric SC display a more prominent loss in strength of TAD borders. Together, our results implicate 3D chromatin extensively reorganizes at multiple architectural levels and underpin the transcriptome remodeling during SC lineage development and SC aging.