What is cellular vision?

Cellular vision refers to the ability of cells to detect and respond to light. Fluorescence microscopy is a powerful tool for studying cell biology, but the resolution is limited by diffraction. Visible light, with a wavelength of 400-700 nm, is used, so subcellular structures or objects spaced less than a wavelength apart cannot be resolved.

Lother Schermelleh and colleagues have now managed to overcome the limit of light microscopy while retaining the advantages of light microscopy and the specificity of cellular imaging. They use a technique known as three-dimensional structural microscopy (3-D SIM) to overcome the problem of resolution limit.

Advantage of cellular vision over conventional microscopic techniques

The structured-illumination microscopy (3D-SIM) technique overcomes the diffraction limit by using multiple beams of interfering light (in the 3D case, three beams are used). The light emitted from the sample contains more detailed information than before, which is shown by a shift in the reciprocal (Fourier or frequency) space. This change is detectable through changes in the image. The additional information carried by the light can be used to reconstruct small features and to achieve resolutions that are twice as high as those of conventional images created without this technique.

This is not the first time that subdiffraction resolution has been achieved in optical microscopy; however, most of the methods developed so far come with drawbacks. For instance, the enhanced resolution is only attainable in one particular direction, or in the near or evanescent field, or the methods are incompatible with standard sample preparation protocols. 3D-SIM provides a significant advantage by allowing the detection of three wavelengths using standard fluorescent dyes. In addition, 3D-SIM provides optical sectioning and resolution enhancement in both lateral and axial directions.

Uses of 3D-SIM technique

Schermelleh and colleagues use 3D-SIM to study mammalian tissue cells, resolving individual nuclear pores and visualizing higher-order features of chromatin. In particular, they image the positions of nuclear lamina (dense 30- to 100-nm-thick networks of protein filaments). This technique can pick up a number of features and new insight into nuclear periphery substructure that is not detectable with conventional microscopy. The researchers are able to obtain detailed insights into the exclusion of chromatin and nuclear lamina from nuclear pores. They can also detect invaginations of the nuclear envelope, which have so far only been detected using transmission electron microscopy. The resolution achieved in both the axial and lateral directions is approximately 100 nm, which is a twofold improvement on conventional microscopy. This could open up new avenues in molecular cell biology.

Reference

Nature Photonics, Vol 2, August 2008, p. 464.