Terhzaz S, Cabrero P, Chintapalli VR, Davies S, Dow JAT. Mislocalization of mitochondria and compromised renal function and oxidative stress resistance in Drosophila SesB mutants. Physiol Genomics 41: 33-41, 2010. First published December 15, 2009 doi:10.1152/physiolgenomics.00147.2009.-Mitochondria accumulate at sites of intense metabolic activity within cells, but the adaptive value of this placement is not clear. In Drosophila, sesB encodes the ubiquitous isoform of adenine nucleotide translocase (ANT, the mitochondrial inner membrane ATP/ADP exchanger); null alleles are lethal, whereas hypomorphic alleles display sensitivity to a range of stressors. In the adult renal tubule, which is densely packed with mitochondria and hence enriched for sesB, both hypomorphic alleles and RNA interference knockdowns cause the mitochondria to lose their highly polarized distribution in the tissue and to become rounded. Basal cytoplasmic and mitochondrial calcium levels are both increased, and neuropeptide calcium response compromised, with concomitant defects in fluid secretion. The remaining mitochondria in sesB mutants are overactive and maintain depleted cellular ATP levels while generating higher levels of hydrogen peroxide than normal. When sesB expression is knocked down in just tubule principal cells, the survival of the whole organism upon oxidative stress is reduced, implying a limiting role for the tubule in homeostatic response to stressors. The physiological impacts of defective ANT expression are thus widespread and diverse. Drosophila melanogaster; Malpighian tubule; adenine nucleotide translocase; mitochondria MITOCHONDRIA ARE ESSENTIAL organelles for the function of all aerobic cells, as they produce ATP, buffer cytosolic calcium, and sequester apoptotic factors. Impairment of mitochondrial function, resulting in excitotoxic metabolic insufficiency, cell death, and oxidative damage, can contribute to severe tissue pathologies and diseases (36,44). Mitochondria are also highly dynamic, and accumulate at sites with particularly high ATP consumption (3,13,17,31,37).The mitochondrial adenine nucleotide translocase (ANT) is the most abundant protein of the inner mitochondrial membrane and a crucial component in the maintenance of cellular energy homeostasis, as well as in the formation of the mitochondrial permeability transition pore (2, 15). It catalyzes ADP/ATP exchange across the mitochondrial inner membrane (24) and thus has the potential to allow mitochondrial sensing of subcellular ATP:ADP poise. ANT is a target of oxidative damage, and functional inactivation has been associated with chronological age as well as physiological age (51). In mammals, the majority of species, including humans, possess three distinct genes for ANT (9,25,26,28). Drosophila harbors two overlapping ANT genes, ANT1 (sesB), and ANT2, with 72% nucleotide identity with 78% amino acid sequence identity (52). Mutations affecting ANT1 in Drosophila were originally identified as a stress-sensitive strain of animals (sesB) that are condi...