Mitochondria-ER contact sites (MERCs) enable communication between ER and mitochondria and serve as platforms for many cellular events, including autophagy. Nonetheless, the molecular organization of MERCs is not known, and there is no bona fide marker of these contact sites in mammalian cells. In this study, we designed a genetically encoded reporter using split super-folder GFP protein for labeling MERCs. We subsequently analyzed its distribution and dynamics during the cell cycle and under normal or stressful cellular conditions such as starvation, apoptosis, and ER stress. We found that MERCs are dynamic structures that undergo remodeling within minutes. Mitochondrial morphology, but not ER morphology, affected the distribution of MERCs. We also found that carbonyl cyanidem-chlorophenyl hydrazone (CCCP) and oligomycin A treatments enhanced MERC formation. The stimulations that led to apoptosis or autophagy increased MERC signals. In contrast, increasing cellular lipid droplet load did not change the pattern of MERCs.
Two very talent graduate students Zhaoying Yang and Xiaocui Zhao finished this work with the help from Jiashen Xu and Weina Shang. Dr. Chao Tong is the correspondence author. This study was supported by National Natural Science Foundation of China, Natural Science Foundation of Zhejiang Province, China, National Key Research & Developmental Program of China, and Fundamental research funds for the central universities.
