Luciferase: Shining a Light to See Inside Living Animal Models

Wed, 01/30/2013 - 16:11

The luciferase reporter is a valuable tool for research into physiology and disease. Light emitted from luciferase enables the monitoring of xenografted tumors, specific cell types, gene expression and pathogens within live animals over time using bioluminescence imaging (BLI) technology. Further detail can be revealed through the use of luciferase antibodies.

Luciferases are a class of enzymes (produced by a variety of organisms) that generate light by acting on substrates (called luciferins). This is a form of chemiluminescence, where the source of the energy emitted as a photon is a chemical reaction, as opposed to absorption of light as in fluorescence.

Immunofluoresence: Luciferase Antibody

Luciferases are commonly utilized as reporter genes, particularly the luciferase from firefly. One interesting application of this in recent years has been bioluminescence imaging (BLI), a noninvasive technique that measures the location and brightness of luciferase reporters in whole, living small animals, typically mice. This is exciting because changes in the luciferase luminescence can be tracked in individual mice (by measuring at multiple time points, e.g. hours, days or weeks), enabling accurate monitoring of dynamic biological processes (such as pregnancy or bacterial infection), and avoiding the need to euthanize numerous mice for invasive analysis at each time point. BLI is sensitive (with very low background) and inexpensive.

The expression of the luciferase reporter gene is dictated by the particular regulatory sequences (such as promoters) of the designed DNA constructs. For example, tumors may be labeled using a constitutively expressed luciferase transgene, implanted into mice, and then monitored using BLI (e.g. to study metastasis or drug response); specific cells in the body (for example pancreatic beta cells, which secrete insulin) may be visualized by linking the luciferase gene to a promoter of a gene only expressed in those cells; and activation of a particular gene by certain conditions (hypoxia, for instance, relevant to cancer research) can be examined by linking the relevant response element to the luciferase reporter gene.

BLI does have limitations, such as a relatively low resolution; but the luciferase reporter can also be detected using complementary techniques. This is where the traditional antibody applications really shine, providing valuable additional detail. For instance, a luciferase antibody can be used to identify the precise location of specific luciferase-expressing cells in tissue sections (mammary stem cells in the mouse mammary gland, for example). IHC staining patterns obtained with the luciferase antibody can also be compared to sections probed for other molecules (analysis of colocalization/coexpression). Western blotting with a luciferase antibody can similarly confirm/determine the location (e.g. particular tissue) of luciferase expression, as well as allowing comparison of the expression of the luciferase reporter with that of other genes of interest. Furthermore, bioluminescence imaging is still a relatively new technology, so IHC and western blots etc. are employed to verify BLI systems and findings.

The future is bright for biomedical research with luciferase!

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Written by Carly Hammond

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