When studying an organism that is very small, it is important to use an imaging technique that will give the clearest picture of shapes and structure. Two-dimensional images can give snapshots of an area, but they cannot truly represent the structure of a three-dimensional object. Dr. Nicastro’s lab uses a technique called cryo-electron tomography to image cells three-dimensionally at a very high resolution.
An electron microscope uses a beam of electrons to image a specimen, instead of the beam of light used by traditional microscopes. The electron beam offers a higher resolution than a light beam would, but because the electrons have to travel through a vacuum the specimen needs to be protected. Dr. Nicastro uses a method of fast freezing that preserves the cell structure more than a dehydration technique would. Tomography is a process of taking a series of two-dimensional images from different angles, and then using the images to reconstruct a three-dimensional view. This 3D image can then be rotated on a monitor, so that organelle structure and placement can be examined from all angles.
Dr. Nicastro showed examples of work that she has done using this technique, including imaging of eukaryotic flagella. Flagella are used by the cell in locomotion, but their function is not yet understood. Tomographic imaging was able to show a structure of microtubules that compose the flagella, as well as the protein dynein that is responsible for the movement of each microtubule. Each microtubule moves in relation to its neighbor, and this is thought to be the process by which speed and propagation of movement in these cells is controlled. This level of detail would not be available using other types of imaging.
