An Introduction To C. Elegans
An introduction to C. elegans: this simple, free-living soil nematode has allowed scientists to discover a wealth of information about human biology. Learn more about this creature.
Caenorhabditis elegans is a beautiful creature. Though only one millimeter in length as an adult, this simple, free-living soil nematode has allowed scientists to discover a wealth of information about human biology. How can one species of worm teach us so much? What could humans possibly have in common with a microscopic worm? Lots of things.
C. elegans isn’t very different from humans at the most basic cellular and molecular level. Worms must replicate their DNA, develop tissues and organs, sense their environment, and navigate through complex media. One of the most remarkable aspects of C. elegans biology, however, is its nervous system.
Neurons are highly specified cells that are designed to carry information quickly from one area to another. Like most nucleated cells, neurons transcribe genes and translate proteins, transport nutrients and waste across cell membranes, and communicate through cell-to-cell contact. One unique feature of neuronal communication is through synaptic transmission—cells talking across a gap. An electric impulse is sent through a neuron, stimulating the release of many compounds and proteins called neurotransmitters (NT). The NTs diffuse across the gap, or synapse, and bind to specialized NT receptor proteins on another cell. That’s how the human brain works, and every other nervous system down to the lowly worm. Recently, the C. elegans genome sequence was completed, allowing scientists to view the creature from a wholly genetic perspective. Comparison between known human genes and predicted genes in C. elegans suggests that the worm has many of the same neurotransmitter biosynthetic enzymes, synaptic release mechanisms, and neurotransmitter receptors. For neurobiological research, C. elegans has become as ideal model organism for study.
While C. elegans is similar to humans at the cellular level, there are some distinct differences that researchers can also take advantage of. First, C. elegans is easily cultured in the lab in large numbers. Millions of worms can live and grow on a lawn of bacteria as small as a musical compact disc. The short life cycle of these worms (3-4 days at room temperature) allow scientists to monitor development and behavior over many generations. And, most importantly, C. elegans has a simple nervous system of only 302 neurons. Scientists have determined the exact locations of each neuronal contact, all gap junctions and synapses to other neurons and cells. Knowing this, specific circuits of neurons can be studied as a model for neuronal circuitry in higher organisms (sensory stimulation, neuromuscular junction development and function, etc.). Powerful molecular and genetic tools can be utilized to study C. elegans neurobiology that would never be possible in a complex mammalian nervous system. For example, specific proteins of interest can be labeled with a fluorescent tag. As the worm develops, the tagged protein is readily visible in every cell that requires it. Using different fluorescent markers, scientists can see if two proteins co-localize, adding insight to their function. Another powerful genetic tool involves a recent discovery called "RNA interference" or RNAi. A gene of interest can temporarily be "turned off" by injecting double-stranded RNA of the reverse complement sequence. More permanent gene deletions can be generated through the imprecise excision of transposable chunks of DNA. These are only a few of the many tools scientists can use to study neurobiology of the worm.
C. elegans has provided a bountiful field of research in which scientists can make monumental discoveries. Though tiny, it is a powerful animal. Though a worm, it is beautiful.
Sources for this article and where to find more information:
Chalfie, M., Jorgensen, E., C. elegans neuroscience: genetic to genome, Trends in Genetics 14 ;12 pp. 506-512 (1998)
Bargmann, C. Neurobiology of the Caenorhabditis elegans Genome, Science 282 pp. 2028-2032 (1998)
Brownlee, D., Fairweather, I. Exploring the Neurotransmitter labyrinth in nematodes, Trends in Neuroscience 22;1 pp. 16-24 (1999)
http://elegans.swmed.edu/ --C. elegans WWW server, maintained by worm researchers. Gives information on current worm research, meetings, and publications.