Figure 3. High magnification time series of mitochondrial fusion and fission in neuronal processes (DrOF). (A) Representative images of rat cortical neurons (8 DIV) cotransfected with mito-RFP and mito–PA-GFP at 7 DIV. In the red channel, mitochondria were selected for photoactivation at 405 nm (circled areas), thereby activating green fluorescence (right). (B) Selected images (merge of red and green channels) from a series of 90 frames taken at 10-s intervals reveal a rare photoactivated mitochondrion undergoing two fission events to produce three mitochondria that subsequently migrate out of view (yellow arrows). Dotted lines approximately outline the neuronal process (see Video 2, available at http://www.jcb.org/cgi/content/full/jcb.200809060/DC1). (C) Example of a photoactivated mitochondrion (green arrows) that fuses to a neighboring unactivated (red) mitochondrion (see panel B and Video 4).