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From Jellyfish to Cancer Cells - Why Fluorescent Proteins Are Crucial to Biomedical Research

June 12, 2017

 

By Meghan Krizus

  Fluorescent proteins allow us to visualize cellular structures. Here, cell membranes are marked with GFP (green), and cell nuclei with mCherry (red). This strain, OD95, was  provided by the CGC, which is funded by NIH Office of Research Infrastructure Programs (P40 OD010440).
 

Fluorescent proteins allow us to visualize cellular structures. Here, cell membranes are marked with GFP (green), and cell nuclei with mCherry (red). This strain, OD95, was provided by the CGC, which is funded by NIH Office of Research Infrastructure Programs (P40 OD010440).

Brightly glowing cells frequently grace the covers of scientific journals in an array of vivid colours. While often beautiful, their significance to scientific research may not be immediately evident. Put more simply: why do our experiments glow, and why is this important?

Many of us have seen images like those of white lab mice that glow green under UV light and have wondered, perhaps, what value exists in such a trait. And while terms like “GFP” are thrown around in mainstream media, one might even wonder not only what these terms mean, but also how and why scientists make everything from human cell lines to single yeast cells express such a beautiful variety of luminescence.

So what are fluorescent proteins? Fluorescence, the ability of a substance to absorb and reemit light, is the key characteristic that allows these proteins to glow when exposed to specific types of light. This process is distinct from bioluminescence which occurs when chemical reactions within an organism (such as a firefly) allow it to produce light without an external source.

Possibly the most famous fluorescent protein is GFP (green fluorescent protein), derived from the jellyfish Aequorea victoria. Naturally emitting green light when exposed to ultraviolet (UV) light, scientists have also modified this protein to create forms that emit light in colours such as yellow (YFP) and blue (EBFP). Nor are GFP-derived fluorescent proteins the only ones in use; as these proteins are widespread in nature, organisms such as corals of the Discosoma genus have allowed development of fluorescent proteins in other colours, such the brilliant red mCherry.

Then how is GFP, or another fluorescent protein, expressed by a cell or organism that does not naturally carry it? In order to make a tissue fluoresce, the genetic material for this fluorescent protein is artificially introduced into the genome, fused to a part or the whole of the coding sequence for a gene of interest. While many methods may be used to accomplish this (CRISPR/Cas9 being one of the newest and most exciting), the end result is that fluorescence is visible wherever the gene is expressed.

Possibly the most important question is, then, why use fluorescence? There are many crucial applications. Perhaps the most important is that fluorescent proteins allow scientists to visualize their experiments – to reveal what might otherwise have been invisible in the form of bright, glowing colour. Furthermore, proteins like GFP allow scientists to observe and image their experiments in live cells. This means that cells or organisms may be observed under a microscope in real time while they are still alive, such as we at the LTRI do when imaging our experiments at our state-of-the-art OPTIMA facility.

One of the most common uses of fluorescent proteins is to visualize where in a cell a protein is present. By fusing a protein such as GFP to a gene of interest, we can determine how and where the protein coded by this gene is expressed. Labeling proteins with a visible marker also allows us to see how the protein changes under different conditions, such as a change in the expression of other genes, or the application of a molecule, such as a drug.

Light-emitting proteins also allow us to visualize specific cells within an organism or specific structures within a cell. A seminal example exists in the field of connectomics, with the “brainbow” mouse. In this mouse line, scientists used an array of fluorescent proteins to mark individual neurons within the animal’s brain, allowing them to study how these neurons interact with one another and providing insight into how mammalian nervous systems–including human ones–function.

It is difficult to overstate the significance of fluorescent proteins, except to say that much (if not most) of current biomedical research would be much less informative without them. The 2008 Nobel Prize in Chemistry, shared by Drs. Osamu Shimomura, Martin Chalfie, and Roger Tsien, awarded for the discovery and development of GFP, speaks to the significance and impact of this discovery. Moreover, as scientists and non-scientists alike might not have anticipated that the study of a fluorescent protein in jellyfish could have created such a cornerstone of biomedical research, GFP and its relatives are a testament to the critical importance of fundamental research.
 

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