Tomographic three-dimensional reconstruction of cilia ultrastructure from thick sections.

We have applied a computer-based tomographic technique to reconstruct the three-dimensional ultrastructure of newt lung cilia. Epon-embedded samples were cut into 0.25-micron-thick sections that were imaged at 1 MV with a high-voltage electron microscope. For the reconstruction shown, a tilt series of 53 micrographs was taken at tilt angles between -54 degrees and +50 degrees. The reconstruction was accomplished from these projections using a weighted back-projection algorithm. The 12-nm resolution of the reconstruction was sufficient to resolve the outer doublet and central pair microtubules, dynein arms, radial spokes, and central sheath structures. The reconstruction can be viewed from various angles and with appropriate parts cut away to reveal structural features of interest. The sense of depth in these views can be enhanced by stereo viewing of shaded surface images. From this reconstruction, we determined that newt lung cilia contain the more common triplet grouping of radial spokes.