Templated insertions—DNA repair gets acrobatic

Abstract

Deletions associated with the repair of DNA double‐strand breaks is a source of genetic alternation and a recognized source of disease‐causing mutagenesis. Theta‐mediated end joining is a DNA repair mechanism, which guarantees deletions by its employment of microhomology (MH) alignment to facilitate end joining. A lesser‐characterized templated insertion ability of this pathway, on the other hand, is associated with both deletion and insertion. This mechanism is characterized by at least one round of polymerase θ‐mediated synthesis, which does not result in successful repair, followed by a subsequent round of polymerase engagement and synthesis that does lead to repair. Here we focus on the mechanisms by which polymerase θ introduces these insertions—direct, inverse, and a new class which we have termed strand switching. We observe this new class of templated insertions at multiple loci and across multiple species, often at a comparable frequency to those previously characterized. Templated insertion mutations are often enriched in cancer genomes and repeat expansion disorders. This repair mechanism thus contributes to disease‐associated mutagenesis, and may plausibly even promote disease. Characterization of the types of polymerase θ‐dependent insertions can provide new insight into these diseases and clinical promise for treatment.

Inspiring basic and applied research in genome integrity mechanisms: Dedication to Samuel H. Wilson

“…Analysis of TINS repair products from a CAS9-geneared DSB at the Lamin B Receptor locus in human retinal pigment epithelial cells (RPE1), ssTINS was found to account for 30% of TINS repair products and was dependent on Pol theta (Stroik et al, 2024). Furthermore, the authors discussed how TINS serves as a driver or passenger mutation in cancer, and how Pol theta-mediated TINS is associated with CAG repeat expansion and associated genetic disorders (Stroik et al, 2024). Future characterization of TINS mechanisms will help to provide novel insight into therapeutic treatment options.…”

“…with emphasis on their importance for basic and environmental health sciences. This SI includes two research articles, one brief communication, and four reviews (Hoag et al, 2024;Hua & Sweasy, 2024;Hussen et al, 2024;Minko et al, 2024;Sobol, 2024;Stroik et al, 2024;Wilson & Wyrick, 2024). The findings and perspectives from this SI may help to better understand how DNA damage and DNA repair mechanisms can provide novel insights into environmentally-induced human disease such as cancer.…”

“…DNA polymerase theta contains both helicase and polymerase activities and plays critical roles in conventional MMEJ, which requires microhomology searching and annealing and often leads to deletions of nucleotides (Ramsden et al, 2022). More recently, DNA Polymerase theta is found to be involved in another type of DNA repair termed Templated Insertions (TINS) that often causes insertions (Ramsden et al, 2022;Stroik et al, 2024). Stroik et al summarized three classes of TINS: intermolecular direct repeat TINS (drTINS), intramolecular inverted repeat TINS (irTINS) and strand switching TINS (ssTINS) (Stroik et al, 2024).…”

“…More recently, DNA Polymerase theta is found to be involved in another type of DNA repair termed Templated Insertions (TINS) that often causes insertions (Ramsden et al, 2022;Stroik et al, 2024). Stroik et al summarized three classes of TINS: intermolecular direct repeat TINS (drTINS), intramolecular inverted repeat TINS (irTINS) and strand switching TINS (ssTINS) (Stroik et al, 2024). Analysis of TINS repair products from a CAS9-geneared DSB at the Lamin B Receptor locus in human retinal pigment epithelial cells (RPE1), ssTINS was found to account for 30% of TINS repair products and was dependent on Pol theta (Stroik et al, 2024).…”

“…Stroik et al summarized three classes of TINS: intermolecular direct repeat TINS (drTINS), intramolecular inverted repeat TINS (irTINS) and strand switching TINS (ssTINS) (Stroik et al, 2024). Analysis of TINS repair products from a CAS9-geneared DSB at the Lamin B Receptor locus in human retinal pigment epithelial cells (RPE1), ssTINS was found to account for 30% of TINS repair products and was dependent on Pol theta (Stroik et al, 2024). Furthermore, the authors discussed how TINS serves as a driver or passenger mutation in cancer, and how Pol theta-mediated TINS is associated with CAG repeat expansion and associated genetic disorders (Stroik et al, 2024).…”