Spatiotemporal filtering in calcium control of mitochondrial function

Calcium plays a central role in all cells and tissues, so the monitoring of cellular calcium is of major importance in both life sciences research and drug development. The critical contribution of cell organelles (mitochondria or nucleus, for example) to the health of the cell has led to the development of methods in which calcium signals in these organelles can be measured. To this end, we have successfully developed calcium indicators (reporters) to track calcium events in organelles in living organisms (the fruitfly, Drosophila melanogaster). We have made the first fruitflies which express calcium reporters in the mitochondria. The mitochondria are powerhouses which generate energy for the cell, and calcium signals are an important part of this process. Malfunction of mitochondrial calcium has been implicated in many disease processes and as most cells have distinct populations of mitochondria, determining the specific function of these in intact tissue would be novel and useful. At a cellular level, fruitflies and humans are very similar; so the fruitfly is an excellent model in which to study mitochondrial calcium signalling in an intact tissue or animal. These studies will allow us to find out how calcium signalling processes in this important organelle affects tissue function in a non-disease situation.

Calcium signalling plays a central role in all cells and tissues, so the monitoring of intracellular calcium events is of major importance in both life sciences research and drug development. The differing contributions of intracellular compartments to calcium signals in all cells has led to the development of calcium reporters, which can be successfully targetted to specific intracellular compartments. Thus, calcium signals in particular organelles can be assessed. We have successfully developed a fluorescent calcium reporter which monitors calcium levels in mitochondria ('mitycam'), and have generated transgenic Drosophila (using the GAL4/UAS system) for both this reporter, as well as as mitochondrially-targeted aequorin. These distinct reporters allow the spatio-temporal resolution of mitochondrial calcium (mitycam) as well as measurement of mitochondrial calcium concentration levels (aequorin). Thus, we intend to use these in vivo mitochondrial calcium reporters to determine the role of calcium in differentially regulating function in dynamic sub-populations of mitochondria in a polarised tissue, in mutants of mitochondrial function, and under hormonal stimuli. Given that mitochondria are involved with generation of reactive oxygen species, we will also investigate the role of mitochondrial calcium in oxidative stress, and will correlate this with whole organism studies.