Using Green Fluorescent Protein to Visualise Cells: a Technology Review

glofishZebra Danio fish fluoresce neon colours

Do you remember the episode about Sheldon’s goldfish – the fluorescent goldfish – in The Big Bang Theory? I always wondered how a goldfish could glow, and now I know it is due to a variant of Green Fluorescent Protein (GFP). Let’s talk about the history and development of GFP.

In the early 1960s, Osamu Shimomura and his colleagues first isolated GFP from a jellyfish called Aequorea victoria. Since this protein could glow in jellyfish, scientists wondered if it could be used to make other creatures glow. In 1994, Martin Chalfie and his co-workers successfully expressed GFP in the sensory neurons of a roundworm. Later, Roger Tsien and his group created genetically modified variants of GFP, extending the fluorescence to emit in the entire visible spectrum and increasing its brightness and stability. So that’s why Sheldon’s goldfish could glow bright yellow on his bedside table.

So, how does GFP and its variants enable creatures to glow? The basic technique is to fuse the GFP gene to the gene of the protein of interest, using the correct base pairs. Once GFP and the protein are synthesized together, the protein will be visible due to the fluorescence of GFP when excited by the right wavelength of light. This allows scientists to visualise the inner workings of living cells, by identifying the location and movement of the proteins of choice! Adrienne Hardham of the ANU Research School of Biology stated, “Because GFP-tagged proteins can be observed in living cells, GFP technologies have made a major contribution to our understanding of cellular processes.” Fluorescing creatures like Sheldon’s fish have inherited genes of GFP and its variants, so that they are expressed in every one of their cells.

So, apart from creating luminous creatures, scientists also use GFP and its variants as valuable medical research tools. The ability to visualize dynamic intracellular processes allows GFP and its variants to be used as markers, biosensors or labels, to study the progression of Alzheimer’s disease in the brains of mice, the effect of Brucella vaccines, the protein dynamics in yeast, and much more.

Cancer is one of the most serious illnesses in the world. I was curious about the application of GFP and its variants in cancer research. If we can visualize the mechanisms of cancer cells, can we produce better ways to cure this disease? GFP and its variants enable scientists to visualize, in real time, the dynamics of cellular processes of cancer cells in living organisms. These processes include cell division, cell death and cell-cycle position. Cancer cells can also be observed as they spread to other sites in the body, and as they are treated with chemotherapy. The ability of scientists to understand the inner workings of cancer cells in living organisms is a vital for the development of treatments. Scientists are now able to evaluate the efficacy of therapeutic anticancer therapies due to the ability to observe cancer cells during treatment.

Another fantastic application of GFP and its variants is the labelling of tumours so that, with fluorescent guidance, doctors can remove the tumours completely. One study published this year by Yano and his coworkers found a lower rate of cancer recurrence after fluorescence-guided surgery. Researchers performed a comparison experiment in two groups of mice to remove liver cancer with fluorescence-guided surgery and conventional bright-light surgery. The study found that fluorescence-guided surgery could help completely remove the spread of liver cancer, resulting in a much lower rate of recurrence – 19% compared to 94%, 120 days after resection – and prolonged survival of the mice. In the future, cancer patients may greatly benefit from GFP.

Personally, I feel grateful and thankful for the scientists who insisted on studying GFP and its variants. There was a gap in research between the 1960s when Osamu Shimomura first isolated GFP and the 1990s when scientists successfully applied it in living cells. I can’t image how difficult it was to fight against failures and to persist with experiments during that time. Science is a field that requires the hard work of many generations. I have a deeper appreciation for the impact of this technology after reading stories of the researchers working on GFP – hopefully, you can now appreciate this technology like I do.

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