Tagging and tracking individual networks within a complex mitochondrial web with photoactivatable GFP.
Assembly of mitochondria into networks supports fuel metabolism and calcium transport and is involved in the cellular response to apoptotic stimuli. A mitochondrial network is defined as a continuous matrix lumen whose boundaries limit molecular diffusion. Observation of individual networks has proven challenging in live cells that possess dense populations of mitochondria. Investigation into the electrical and morphological properties of mitochondrial networks has therefore not yielded consistent conclusions. In this study we used matrix-targeted, photoactivatable green fluorescent protein to tag single mitochondrial networks. This approach, coupled with real-time monitoring of mitochondrial membrane potential, permitted the examination of matrix lumen continuity and fusion and fission events over time. We found that adjacent and intertwined mitochondrial structures often represent a collection of distinct networks. We additionally found that all areas of a single network are invariably equipotential, suggesting that a heterogeneous pattern of membrane potential within a cell's mitochondria represents differences between discrete networks. Interestingly, fission events frequently occurred without any gross morphological changes and particularly without fragmentation. These events, which are invisible under standard confocal microscopy, redefine the mitochondrial network boundaries and result in electrically disconnected daughter units.
Department of Pharmacology and Experimental Therapeutics, Tufts University, 136 Harrison Ave., Boston, MA 02111, USA.
Gilad
G
Twig
Solomon A
SA
Graf
Jakob D
JD
Wikstrom
Hibo
H
Mohamed
Sarah E
SE
Haigh
Alvaro
A
Elorza
Motti
M
Deutsch
Naomi
N
Zurgil
Nicole
N
Reynolds
Orian S
OS
Shirihai
D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D049452:Green Fluorescent Proteins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D020014:K562 Cells; D008564:Membrane Potentials / Q000502:physiology; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000737:chemistry / Q000378:metabolism*; D051336:Mitochondrial Membranes / Q000737:chemistry / Q000378:metabolism*; D013194:Staining and Labeling / Q000379:methods
D049452:Green Fluorescent Proteins