Mitochondria possess their own genome that encodes 13 proteins – a relatively small number. Imaging mitochondrial protein expression is limited to traditional immunofluorescence analyses of individual proteins, and does not reveal dynamic changes or rates of overall translation. In their Tools and Resources paper on page 4193, Andrew Hamilton and colleagues describe a new method for imaging mitochondrial translation in situ. Their method is based on previous methods for imaging total cytoplasmic translation, but extends these to allow the imaging of the far lower output of mitochondrial translation. Finding that existing methods produce excessive background signal, the authors show that cell permeabilisation before cell fixation greatly reduces background fluorescence after labelling with the ‘clickable’ Met analogue homopropargylglycine (HPG). They then demonstrate the distribution in position and intensity of mitochondrial translation within cells, as well as comparing mitochondrial translation between cells. They find substantial natural variation in translational output between mitochondria and only a weak correlation with mitochondrial genome copy number. Using this method, the authors also show that mitochondrial translation persists during mitosis when cytoplasmic translation is suppressed. This new technology provides a simple, rapid and inexpensive method for the in situ detection of mitochondrial translation, and should be of great benefit to those studying mitochondrial cell biology.
