Utilizing Biological Phenoma to study Biology: Bioluminescence
Quick: Is the glowing water in this picture photoshopped or real?The correct answer is real! Yes, there is such a thing as naturally occurring glowing water. And it is made possible by a phenomenon called bioluminescence.
Bioluminescence is a chemical reaction that happens in a living organism to produce a beautiful glow. Last month a few of my friends were swimming at La Jolla Shores and noticed that the water around them lit up with every movement of their bodies. What made the water glow? Phytoplankton emitting light when agitated—every movement from waves, currents, fish, or, in this case, swimmers, sent colorful flashes throughout the water. Wanting to witness it for myself, we went out again to experience the “glowing waves”. Unfortunately, we were too late in the season to experience the full beauty of bioluminescent plankton lighting up the waves, but by rapidly swishing our hands underwater, we were still rewarded with small sparks of light. Although my encounter with bioluminescence fell short that evening, I do get to see it in action every day in the lab.
Today I introduce how scientists utilize bioluminescent properties to study biological phenomena at the molecular, cellular, and organism level. Throughout history humans have benefited from the natural glow produced by bioluminescent organisms such as the use of dried fish skins as a source of light in coal mines instead of lamps. Usage of these organisms has led researchers to ask the question: what makes these organisms glow? Seeking to understand bioluminescence at a molecular level has led researchers to produce fluorescent “tags”. These “tags” can be attached to an unlimited number of molecules and proteins to answer fundamental biological questions.
Bioluminescence is a chemical reaction that takes place in a living organism to produce light. Although the most well-known organism to produce this glow might be the firefly, the majority of bioluminescent creatures are found in the ocean. Different organisms may vary in how they produce their unique glow, but the basic mechanism involves the enzyme* luciferase reacting with the light-emitting compound luciferin to produce light.
The beauty of naturally-glowing living organisms led researchers to investigate the underlying chemistry of this unique phenomenon. One researcher, Osamu Shimomura, began a lifelong relationship with bioluminescence when he found the structureǂ of luciferin in 1955. What followed was a quest to discover how different organisms produced their own unique glow. While investigating the bioluminescent jellyfish Aequorea victoria, Shimomura discovered green fluorescent protein (GFP). This discovery, and the consequent development of GFP, revolutionized biology. Scientists could now attach fluorescent proteins, such as GFP, to a molecule of their choice and literally watch biology in action by watching the fluorescently tagged molecules. In 2008, Shimomura, along with Martin Chalfie and Roger Tsien, received the Nobel Prize in Chemistry for their discovery and development of GFP.
Since the discovery of GFP, fluorescent proteins have been developed in a wide variety of colors for an extensive number of molecules and proteins. Although both fluorescent proteins and bioluminescence produce light, they work very differently. Rather than using a chemical reaction, fluorescent proteins produce certain light colors by using energy from other specific wavelengths of light.€ Fluorescent proteins create their unique glow when they are “excited” by a wavelength of light specific to the protein.¥ For example, GFP
emits green light at ~510 nm after shining blue light at ~490 nm on the protein. By manipulating the protein, these light patterns can be optimized to produce different colors!
Researchers can use these proteins to image biological events in real-time and real-space. This process is called fluorescent microscopy. Fluorescent microscopes work by first hitting a sample with an excitation light. A camera attached to the microscope then catches the light emitted from the sample. When specific molecules (proteins, compounds, parts of cells, etc) are tagged with different fluorescent proteins, researchers can watch, analyze, and quantify what is happening—whether this is of molecules by themselves, inside of a cell, or even inside of an organism. Advancing technology in fluorescent proteins, microscopes, and other emerging biological approaches are pushing the limits of how small we can go (can we look at very specific interactions inside of a cell?) and how many things we can watch at the same time (can I see 6 things inside of a cell at the same time rather than only 3?). These advances are enabling us to find answers to critical questions such as:
- Why do some cells act differently than others, even when treated the same? This question has applications in cancer research, healing responses, and why certain drugs work for some people and not others.
- Can we predict the movement patterns of cells in response to a specific stimulation? Take a look at my previous post on wound response to see an example of the importance of understanding cellular movement.
- What are the differences between the actions of a single cell and the actions of a population of cells? Single cells do not always act the same, and yet, a population of cells has a very predictable response. Why?
Although still young, the use of fluorescent proteins in biology is an exciting and continually improving field. By applying fluorescent microscopy to quantitative biology methods, we can better understand biological events to answer some of the most complex biological questions, such as those listed above. Most importantly, the resulting images provide a snapshot into the hidden world of biology by providing a new level of detail into how we function as living organisms.
*An enzyme is a protein that accelerates chemical reactions. Here, it accelerates the chemical reaction that makes luciferin light up.
ǂ In order to understand how things work, scientists often need to first find the structure of their molecule or protein of interest. Structures can be found using a variety of methods.
€ A wavelength of light is a unit of measurement in a light spectrum. That is, each color of light that we see has a specific wavelength—this is the visible light region (390 nm –780 nm).
¥ Each fluorescent protein has a specific excitation spectrum and emission spectrum. A spectrum is a pattern consisting of peaks and valleys at different wavelengths across the visible light spectrum. This spectrum is unique for every fluorescent protein. For example, the spectrum of GFP has an excitation peak at ~490 nm and an emission peak at ~510 nm. The emission spectrum consists of a peak that emits the color for that wavelength – the green that you see in GFP. This happens only after a specific wavelength of light, or the peak found in the excitation spectrum, excites the fluorescent protein.