Crista Junctions of Mitochondria Visualized by Electron Tomography

Electron microscope tomography is a useful method for deriving three-dimensional (3-D) structures from tilt series. We used an intermediate, high-voltage electron microscope operated at 400 kV to study the 3-D structure of selectively stained or labeled mitochondria from diverse sources. We have examined the structure of neuronal mitochondria and mitochondria from brown adipose tissue (BAT) employing either single-axis or double-axis techniques over a tilt range of ±60° with 1° or 2° angular increments (Fig. 1). Although BAT mitochondria contains only lamellar cristae with no tubular cristae as we have observed in neuronal mitochondria, we found that the inner membrane of BAT mitochondria invaginates to form cristae onlythrough narrow, tubular openings or crista junctions(Fig. 2).Recent interest in the possibility of structural artifacts in chemically fixed mitochondria imaged in situmotivated us to perform electron tomography on cryofixed brain and brown fat tissue.