Green fluorescent proteins, or GFPs for short, are visibly advancing research in biology and medicine. By using GFPs to illuminate proteins otherwise undetectable under the microscope, scientists have learned a great deal about processes that take place within our cells. Particularly beneficial are the advances scientists have made in understanding diseases—from HIV to malaria and cancer, to name a few—by utilizing GFPs in their research.
But what are these advances, and how do scientists actually use GFPs in their experiments? In Illuminating Disease: An Introduction to Green Fluorescent Proteins, Marc Zimmer details the stories of many scientists who made great strides in their research by using GFPs. In this slideshow we’ve summarized some of those stories, accompanied by captivating images of GFPs in action.
For over 40 years, Osamu Shimomura studied Aequorea victoria, crystal jellyfish that thrive in the Pacific Northwest. Through his research, Shimomura revealed that A. victoria emit green light through a cellular process that involves two proteins. The first protein, aequorin, emits a blue light energy when it binds to calcium. The second protein absorbs the energy from the aequorin and reemits it as green light. The process of converting the blue light to green light is referred to as fluorescence, and the protein responsible for this conversion is appropriately named green fluorescent protein, or GFP.
GFPs and HEART DISEASE
Scientists often tag other proteins in our cells with GFPs—by binding the GFPs to these proteins—as a way to monitor proteins of interest throughout a variety of biological processes. For example, in humans there is a protein that regulates the calcium levels in our body, and in doing so, this protein controls our heartbeat—the calculated contractions in our muscle cells that take place through reactions with free calcium. To mimic this process, and understand why it’s so important, Andres Villu Maricq scanned the genome of Caenorhabditis elegans to find a regulatory protein similar to the one found in humans. After tagging this protein with GFPs, Maricq could test what happens when this protein’s function is turned off. Depending on location, the regulator protein governed the timing of swallowing, digestions, and fertilization, thus demonstrating the important role regulator proteins play in our bodies.
GFPs and MALARIA
Malaria has been infecting people for as long as humans have been recording history. The disease is caused when a protozoan host called Plasmodium enters the body, and the most common form of transmission is through mosquito bites. Since Plasmodium targets hemoglobin in the blood stream, one common response to malaria is the sickle cell mutation. When the hemoglobin in blood cells of individuals with this genetic mutation are attacked by Plasmodia, the blood cells collapse—thereby inhibiting the parasite from living within the human body. By tagging Plasmodia with GFP, scientists can observe this phenomenon first hand.
GFPs and CANCER
By orthotopically implanting GFP-expressing cancer cells in nude mice—a perfect model organism because nude mice’s immune systems do not reject foreign cells—scientists can observe the development and spread of cancer cells, a process called metastasis. Because they are hairless fluorescence imaging software and scanners allow scientists to view the tumors through the mice’s skin, while they are still alive. Every strain of cancer acts in a different way, and accordingly responds to treatment in various manners. As such, illuminating cancerous tumor activity with GFPs has been very helpful in advancing scientists’ understanding of this disease, because it allows them to witness these varying strains firsthand.
GFPs and HIV/AIDS
One of the deadly aspects of the HIV virus is its ability to kill host T-cells. Scientists such as Gary Nabel and his colleagues have used GFPs to demonstrate exactly how the HIV virus accomplishes this task. Most mammalian cells protect themselves against DNA damage with repair enzymes; however, in HIV activated T cells a special repair enzyme that initiates cell death is released. Nabel and his colleagues revealed this process by illuminating these enzymes with GFPs. Scientists also study HIV/AIDS treatments using GFPs. For example, Eric Poeschla and his colleagues have tested the effectiveness of inserting both a gene known to inhibit HIV-1 and FIV (feline immunodeficiency disorder) in rhesus monkeys and a gene that codes for GFPs into cats. This model for gene therapy in humans with HIV is still under investigation, but seems to be producing positive results.
TO LEARN MORE ABOUT GFPs
To learn more about GFPs and what they have taught scientists about diseases, check out Illuminating Disease: An Introduction to Green Fluorescent Proteins.
Slideshow Image Credits:
Image 1: Aequorea victoria emitting florescent light, courtesy of Steven Haddock.
Image 2: Rhythm proteins within a genetically modified C. elegans, courtesy of Ken Norman, University of Utah.
Image 3: Red blood cells infected with a GFP-expressing strain of malaria. This image was originally published in Nature News and has been used with permission.
Image 4: Breast cancer cells labeled with GFPs. This image was originally published in Cell and has been used with permission.
Image 5: Kitten with GFP-tagged restriction factor from a rhesus monkey, testing its effect on FIV. This image was originally published in Nature Methods and has been used with permission.
Image 6: GFP-expressing spinal motor neurons in a chicken embryo. This image was originally published in Cell and has been used with permission.
Feature Image: Mammalian axons illuminated with GFPs. This confocal image was originally published in Nature and has been used with permission, courtesy of Jean Livet.