Bioluminescent/fluorescent imaging

About this technique

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Bioluminescent imaging is a technique for imaging living small animals such as mice, rats and guinea pigs and is commonly applied to drug development and cancer biology. The technique is non-invasive, as it measures the light emitted from the cells tagged with luciferase. It can be used to track gene expression via a luciferase-tagged protein over time, or by using a cell-specific tag that can allow cell populations to be monitored, as would be useful in the study of cancer cells and tumour progression. Tagged cells can be injected into animals and their behaviour observed.

An example would be cancer cells tagged with luciferase and injected into a specific site of the mice (e.g. tibia) and scanned using bioluminescence. The cells in the bone emit a stronger light as the cancer grows and this helps the researcher to measure tumour growth. Tracking the tumour growth enables researchers to see the beginning of bone loss (osteolysis). New drugs can be trialled on the mice, and their effect on the tumour itself and on the bone destruction, measured.

In most cases, nude mice are used or the region of interest is shaved, as the presence of hair can obscure the signal from the tumour. The animal is anaesthetised in an induction chamber and injected with the appropriate substrate for the luciferase being used. It is then placed in the anaesthesia manifold in the imaging chamber so that the animal's head is securely placed in the nose cone. The subject is then imaged. The luminescent signal level is proportional to the exposure time, and the minimum and maximum exposure times are 0.5 seconds and 5 minutes respectively. The standard image is a composite image of the photographic and luminescent images and represented as an overlay.

Advantages of this application are the use of fewer animals and shorter timelines compared to more conventional animal testing methods. Also, the response to treatment can be measured without terminal histological assessments.