Making worms that glow in the dark

March 8, 2002

The capability to genetically engineer plants and animals so that they glow in the dark began in 1960 in the frigid waters of Puget Sound in the state of Washington. A team of scientists from Princeton University visited the area to collect jellyfish specimens in an attempt to understand the nature of their bioluminescence. Two years later the scientists, Osamu Shimomura and Frank Johnson, published a paper describing the purification of "aequorin", the "chemiluminescent" protein that they thought was responsible for the bioluminescent properties of the jellyfish Aequorea victoria. In the paper, they also noted the existence of a companion protein that exhibits a very bright, green fluorescence when exposed to ultraviolet light. It was an inauspicious beginning for what was to become one of the most widely used and useful tools available to cell biologists.

The molecule — which was dubbed Green Fluorescent Protein, or GFP — remained little more than a scientific curiosity for thirty years. That changed in the 1990's, however, when scientists sequenced the gene that produces GFP and solved its crystal structure. In 1994, a group of scientists inserted the GFP gene in the genome of C. elegans and found that it produced fluorescent GFP molecules within the bodies of the transgenic worms. In the same year, some other scientists performed the same experiment in E. coli. These results paved the way for the use of GFP as a "reporter molecule" in a wide variety of living organisms.

Since 1994, the use of GFP has exploded. It has been used with many other organisms. In addition to C. elegans, it has been used in the fruit fly, zebrafish, mouse and rabbit, among a number of other species. In these cases, bathing the animals in a blue light induces the GFP manufactured in their bodies to emit green light or to "fluoresce." Biologists use genetic methods to direct GFP expression to specific cells or to sub-cellular structures such as mitochondria or synapses in neurons, making these structures literally "glow in the dark" so they can be seen easily in a special fluorescence microscope. Because these "transgenic" animals are alive, GFP labeling allows scientists to directly observe cellular processes as they occur. Different colored GFP proteins can be used simultaneously to observe more than one object in a living animal. The different colors include Cyan (CFP), green (GFP), yellow (YFP) and a red fluorescent protein recently isolated from a species of coral (dsRed). Miller and Dave Piston collaborated with Andrew Fire at the Carnegie Institute of Washington to develop methods for visualizing these different colored fluorescent proteins in C. elegans.

Matthew Herper, Biotech's Glowing Breakthrough, Forbes.com, 26 July 2001

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