Abstract

Laser micro-irradiation can be used to induce DNA damage with high spatial and temporal resolution, representing a powerful tool to analyze DNA repair in vivo in the context of chromatin. However, most lasers induce a mixture of DNA damage leading to the activation of multiple DNA repair pathways and making it impossible to study individual repair processes. Hence, we aimed to establish and validate micro-irradiation conditions together with inhibition of several key proteins to discriminate different types of DNA damage and repair pathways using lasers commonly available in confocal microscopes. Using time-lapse analysis of cells expressing fluorescently tagged repair proteins and also validation of the DNA damage generated by micro-irradiation using several key damage markers, we show that irradiation with a 405 nm continuous wave laser lead to the activation of all repair pathways even in the absence of exogenous sensitization. In contrast, we found that irradiation with 488 nm laser lead to the selective activation of non-processive short-patch base excision and single strand break repair, which were further validated by PARP inhibition and metoxyamine treatment. We conclude that these low energy conditions discriminated against processive long-patch base excision repair, nucleotide excision repair as well as double strand break repair pathways.

Highlights

  • Cellular DNA is constantly exposed to endogenous as well as exogenous genotoxic factors, leading to base damage, photoproducts/adducts or DNA single (SSBs) and double strand breaks (DSBs)

  • Using time-lapse analysis of cells expressing fluorescently tagged repair proteins and validation of the DNA damage generated by micro-irradiation using several key damage markers, we show that irradiation with a 405 nm continuous wave laser lead to the activation of all repair pathways even in the absence of exogenous sensitization

  • Micro-irradiation with 405 nm continuous wave (CW) lasers without exogenous sensitizers was previously shown to induce a mixture of DNA damage, ranging from pyrimidine dimers to DNA double strand breaks [15]

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Summary

Introduction

Cellular DNA is constantly exposed to endogenous as well as exogenous genotoxic factors, leading to base damage, photoproducts/adducts or DNA single (SSBs) and double strand breaks (DSBs) If left unrepaired, these lesions can lead to mutations and subsequently cancer and/or cell death. With the use of a focused laser beam, it is possible to induce DNA damage with a very high spatial resolution and tight temporal control inside of living cells [4] This method can in principle be applied to a large variety of cells to study the kinetics of DNA repair in situ in the context of chromatin. Another great advantage is that with the use of genetically encoded fluorescently-tagged versions of different DNA repair factors it is possible to study their association/dissociation at sites of induced DNA damage in real time with high temporal resolution (reviewed in [5,6,7,8])

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