Some 800 million years have passed since the evolutionary paths of humans and the roundworm C. elegans diverged. Yet, today this tiny, transparent, bacteria-feeding worm serves as an important model organism for scientists studying the biological mechanisms that underlie the development of the human brain and nervous system, and how development can go awry.

C. elegans has many characteristics that make it ideal for such study. It is easy to house and to reproduce. C. elegans also has a short life cycle, which means experiments can be done quickly. And it has far fewer cells than other animals. While the human body contains trillions of cells, C. elegans has less than 1,000. Most important, however, is the worm’s see-through skin, which enables scientists to observe through a microscope its interior cells in action.

As a result of these remarkable characteristics, C. elegans has become a valuable and widely used research tool, one that is playing a central role in helping scientists:

• Achieve a deeper understanding of the cellular development of a multicellular organism and its nervous system.
• Study complex diseases and conditions that affect humans.

Because of the ease of studying cellular development in the roundworm, C. elegans has been used for many research firsts. For example, C. elegans was among the first organism to have its development mapped cell-by-cell, from a single egg to the nearly 1,000 cells in the fully formed adult.

This research helped lead to the discovery of an important cellular process that may be involved in certain cancers and autoimmune disorders. Studies mapping the cellular development of C. elegans revealed that 131 of its cells self-destruct during development. Further research indicated this cell death is programmed into some of the worm’s genes — genes that have counterparts in humans. That discovery, which merited a Nobel Prize, is helping scientists better understand a number of human illnesses in which programmed cell death goes awry. The discovery of antisense RNA (RNAi) also was made in C. elegans, which resulted in another Nobel Prize.

The ability to identify and follow individual cells also allowed researchers to trace the connections between nerve cells. Unlike the human brain, which contains 100 billion nerve cells, C. elegans has just 302, making it easier to map. Researchers created a “wiring” diagram called a connectome of the worm’s nervous system. This map showed how its nerve cells are linked and transmit messages to each other. This information may offer clues about connections in the human brain.

Researchers also used C. elegans to study the development of these brain circuits. Using a Nobel Prize-winning technique to fluorescently label proteins, neuroscientists identified proteins important in the growth of axons, the thread-like projections of nerve cells that transmit messages throughout the nervous system. The failure of axons to grow again after they have been damaged — as the result of spinal cord injury, for example — is a key barrier to effective treatments for paralysis and many other nerve-related disabilities

Scientists have identified specific gene mutations that cause axon growth to go haywire. Perhaps these C. elegans findings might be translated into treatments that stimulate axons to regenerate themselves properly, a process that might help restore movement lost to injury. In this way, research on C. elegans development may lead to new treatments for human conditions.

In addition to cellular development, researchers are studying aging, sensation, and social behaviors in C. elegans. In science, few small things have been the source of as many big scientific breakthroughs as the tiny roundworm C. elegans.