New microscopy makes individual cells visible
A new microscopy technique enables for the first time to selectively visualize individual cells within the complex, three-dimensional tissue of a living organism. An observation led to the new application. The researchers worked with a special class of fluorescent proteins (see box) that change colour when irradiated with laser light of a specific wavelength. One such ‘chameleon protein’ is called Dendra 2, which normally emits green light when illuminated with blue light. The emission of Dendra 2 is however shifted into the red when it is irradiated by intensive violet or ultraviolet (UV) laser light.
The researchers specifically discovered that when Dendra 2 is irradiated by both a blue and a red laser at the same time, the protein’s colour can also change to red. For this dual-colour illumination low intensity laser light is sufficient. In contrast to high intensity violet or UV irradiation it does not damage living cells.
Fluorescent proteins can be used to make whole cells, precise cell structures or single molecules visible. For the first time, the discovery permits a single cell or group of molecules located within a desirable part of a living organism to be highlighted with one colour, while all the other cells or molecules remain visible with another colour.
The researchers have developed a simple and inexpensive colour filter, which can be used with the conventional confocal laser microscopes that are found in many biomedical research institutes. When mounted between the laser source and object, the filter divides the laser light into separate blue and red beams that are directed on to a small focal point on the object.
Examination of dynamic processes
The ability to make individual neurons visible could be of great importance, for example, in the precise mapping of the brain, according to Pantazis. Since the method is suitable for individual cell targeting in living organisms, it could also be used to examine dynamic processes; for example, what happens to individual cells or a group of molecules when researchers treat an organism with active pharmaceutical ingredients. Embryo development could also be examined in more detail.