Methods to Study the Mitochondrial Unfolded Protein Response (UPR) in Caenorhabditis elegans.

The nematode Caenorhabditis elegans is a powerful model to study cellular stress responses. Due to its transparency and ease of genetic manipulation, C. elegans is especially suitable for fluorescence microscopy. As a result, studies of C. elegans using different fluorescent reporters have led to the discovery of key players of cellular stress response pathways, including the mitochondrial unfolded protein response (UPR). UPR is a protective retrograde signaling pathway that ensures mitochondrial homeostasis. The nuclear genes hsp-6 and hsp-60 encode mitochondrial chaperones and are highly expressed upon UPR induction. The transcriptional reporters of these genes, hsp-6::gfp and hsp-60::gfp, have been instrumental for monitoring this pathway in live animals. Additional tools for studying UPR include fusion proteins of ATFS-1 and DVE-1, ATFS-1::GFP and DVE-1::GFP, key players of the UPR pathway. In this protocol, we discuss advantages and limitations of currently available methods and reporters, and we provide detailed instructions on how to image and quantify reporter expression.