DSBforming

DSBforming is a term used to describe the initiation of double-strand breaks (DSBs) in genomic DNA. It encompasses endogenous cellular processes that generate DSBs as part of development and maintenance, as well as intentional breaks introduced by experimental tools. DSBs pose a severe threat to genome integrity because both DNA strands are damaged simultaneously, requiring rapid and accurate repair.

DSB formation occurs in multiple contexts. In meiosis, specialized nucleases such as Spo11 catalyze programmed DSBs to initiate homologous recombination, with the breaks processed by the MRN complex and CtIP/Sae2 to generate resected ends. In the immune system, RAG1/2-mediated cleavage and activation-induced cytidine deaminase can also create DSBs as part of V(D)J recombination and class switch recombination. Replication stress, oxidative damage, and exposure to ionizing radiation or certain chemicals create accidental DSBs. Engineered nucleases, including CRISPR-Cas systems, are designed to introduce DSBs at targeted genomic loci for genome editing.

Repair choices depend on cellular context. DSBs can be repaired by non-homologous end joining (NHEJ) or homologous recombination (HR), with alternative end-joining pathways as backups. The efficiency and pathway choice are influenced by chromatin state, cell cycle phase, and signaling from the DNA damage response, notably ATM/ATR and DNA-PKcs. Unrepaired or misrepaired DSBs can lead to mutations, deletions, translocations, or cell death, contributing to development, aging, cancer, or genome instability.

In research and medicine, understanding DSB formation is essential for understanding genome stability and for harnessing DSBs in gene editing, cancer therapy, and functional genomics.