Fine Structural Features of Complex InDels and NHEJ Repair at Naturally Occurring Damage Sites in Normal Human Colon Crypts

ABSTRACT DNA repair in biochemical and genetic experimental systems permits a precise definition of enzyme requirements and mechanistic steps. Comparing these findings to repair events at naturally occurring damage sites in multicellular organisms is essential for confirming and expanding these insights into a physiologic context. However, heterogeneity in any normal cell population increases with each cell division, and the reliable detection of replication-independent DNA damage sites and their repair has been a major barrier. Here, we examine single human colon crypts, which harbor natural cell clones, using a novel whole-genome sequencing (WGS) method to identify complex insertion-deletion (indel) in the crypt stem cells. Analysis of complex indel events likely repaired by non-homologous end joining occurring in crypt stem cells permits inferences about the in vivo repair of naturally occurring DNA damage within physiologically-relevant chromatin in normal human cells.