Gamma‐H2AX immunofluorescence for the detection of tissue‐specific genotoxicity in vivo

The phosphorylation of histone H2AX in Serine 139 (gamma‐H2AX) marks regions of DNA double strand breaks and contributes to the recruitment of DNA repair factors to the site of DNA damage. Gamma‐H2AX is used widely as DNA damage marker in vitro, but its use for genotoxicity assessment in vivo has not been extensively investigated. Here, we developed an image analysis system for the precise quantification of the gamma‐H2AX signal, which we used to monitor DNA damage in animals treated with known genotoxicants (EMS, ENU and doxorubicin). To compare this new assay to a validated standard procedure for DNA damage quantification, tissues from the same animals were also analyzed in the comet assay. An increase in the levels of gamma‐H2AX was observed in most of the tissues from animals treated with doxorubicin and ENU. Interestingly, the lesions induced by doxorubicin were not easily detected by the standard comet assay, while they were clearly identified by gamma‐H2AX staining. Conversely, EMS appeared strongly positive in the comet assay but only mildly in the gamma‐H2AX immunofluorescence. These observations suggest that the two methods could complement each other for DNA damage analysis, where gamma‐H2AX staining allows the detection of tissue‐specific effects in situ. Moreover, since gamma‐H2AX staining can be performed on formalin‐fixed and paraffin‐embedded tissue sections generated during repeated‐dose toxicity studies, it does not require any further treatments or extra procedures during dissection, thus optimizing the use of resources and animals. Environ. Mol. Mutagen. 60:4–16, 2019. © 2018 Wiley Periodicals, Inc.