Live Cell Imaging to Study Real-Time ATM-Mediated Recruitment of DNA Repair Complexes to Sites of Ionizing Radiation-Induced DNA Damage

Sensors and Inhibitors for the Detection of Ataxia Telangiectasia Mutated (ATM) Protein Kinase

Recruitment and activation of the ataxia telangiectasia mutated (ATM) kinase regulate multiple cell-cycle checkpoints relevant to complex biological events like DNA damage repair and apoptosis. Molecularly specific readouts of ATM using protein assays, fluorescence, or radiolabeling have advanced significantly over the past few years. This Review covers the molecular imaging techniques that enable the visualization of ATM-from traditional quantitative protein assays to the potential use of ATM inhibitors to generate new imaging agents to interrogate ATM. We are confident that molecular imaging coupled with advanced technologies will play a pivotal role in visualizing and understanding the biology of ATM and accelerate its applications in the diagnosis and monitoring of disease, including radiation therapy and patient stratification.

Application of fluorescence lifetime imaging microscopy of DNA binding dyes to assess radiation-induced chromatin compaction changes

In recent years several approaches have been developed to address the chromatin status and its changes in eukaryotic cells under different conditions-but only few are applicable in living cells. Fluorescence lifetime imaging microscopy (FLIM) is a functional tool that can be used for the inspection of the molecular environment of fluorophores in living cells. Here, we present the use of single organic minor groove DNA binder dyes in FLIM for measuring chromatin changes following modulation of chromatin structure in living cells. Treatment with histone deacetylase inhibitors led to an increased fluorescence lifetime indicating global chromatin decompaction, whereas hyperosmolarity decreased the lifetime of the used dyes, thus reflecting the expected compaction. In addition, we demonstrate that time domain FLIM data based on single photon counting should be optimized using pile-up and counting loss correction, which affect the readout even at moderate average detector count rates in inhomogeneous samples. Using these corrections and utilizing Hoechst 34580 as chromatin compaction probe, we measured a pan nuclear increase in the lifetime following irradiation with X-rays in living NIH/3T3 cells thus providing a method to measure radiation-induced chromatin decompaction.