(d) Cells were transfected with either control siRNA or with siRNA specific to MFN1/MFN2, IRGM or IRGM and MFN1/MFN2, and then labelled with MTR and analysed for mitochondrial morphologies. Data are means ± s.e.m. (c, n = 3; d, n = 4). Asterisk indicates P 0.05, double asterisks indicate P 0.01 and dagger indicates P > 0.05 (t-test). 