DNA damage and genome instability are hallmarks of ageing. In humans, congenital defects in DNA repair mechanisms such as nucleotide excision repair (NER) lead to increased cancer risk, accelerated ageing including neurodegeneration and developmental growth defects. NER activity is highly conserved in C. elegans and NER deficient animals are incapable of repairing DNA damage inflicted by UV irradiation, resulting in growth arrest and decreased life span. We investigate the tissue-specific and age-dependent activity of NER in maintaining genome stability in C. elegans. To this end, we established an in vivo imaging system to monitor NER activity in C. elegans: We generated transgenic animals expressing the central NER factors XPA-1::GFP or CSB-1::GFP under control of the respective endogenous promoters. In vivo expression analysis reveals a progressive decline of XPA-1::GFP during ageing in all tissues, except the neuronal system. Further, we are performing tissue-specific rescue studies of the highly UVB sensitive
xpa-1 mutant animals by constitutively driving expression of XPA-1::GFP in muscles, intestine, cuticle, and the neuronal system. We apply a UVC laser system for precise single-cell DNA damage induction in cuticle tissue, and observe rapid recruitment of XPA-1::GFP to the site of irradiation. This system allows investigating cell type-specific dynamics of DNA damage response factors during ageing and in the context of a whole organism. To further understand tissue-specific relevance of DNA repair, we created transgenic animals that ectopically express the A. thaliana photolyase PHR1, which specifically repairs cyclobutane pyrimidine dimers (CPDs), which comprise the main lesion type induced by UV. Ubiquitous and constitutive expression of PHR1::GFP enhances UV resistance of wild type and NER deficient animals. Understanding tissue-specific DNA damage responses and genome maintenance in C. elegans will lead to a better understanding of the complex human disorders that are caused by DNA repair defects and allow the development of intervention strategies to counteract age-related tissue-decline and promote longevity.