Trailblazers: Investigating Chemotaxis with C.elegans
Background Information Excerpts from Edvo-Kit #852 If you’ve ever forgotten to take out the garbage or driven by a landfill then you’ve experienced your chemosensory system in action. This system: (1) obtains detailed information about the environ- ment by detecting molecules of diverse chemical structure and (2) determines an appropriate response to this mixture of signals. Our sense of smell and taste drives our food choices, warns us about potential dangers, and can even influence our memories and emotions. Several systems within our body also rely on the ability of single cells to move toward or away from a chemical cue - a phenomenon known as chemotaxis. For example, white blood cells ac- cumulate at the site of injuries and infections by tracking chemicals released by injured tissue and invading bacteria. Impaired chemotaxis has been linked with several health issues including multiple sclerosis, male infertility, Hodgkin disease, AIDS, Chediak-Higashi syndrome, and cancer. Scientist hoping to treat these and others conditions use the simple nervous system of C.elegans to explore the cellular, genetic, and molecular basis of chemotaxis. Why Study C.elegans A model organism is any plant, animal or microorganism that allows us to study fundamental questions in biology that may be hard to study directly in complex organisms like humans. In the 1970s, Dr. Sydney Brenner established the nematode C.elegans as a model organism because they have a simple genome, a fast generation time, and are easy and inexpensive to maintain. While characterizing the worm, Brenner, along with Drs. John Sulston and Robert Horvitz, discovered that the developmental fate of every cell in the worm is invariable between animals. They also discovered key genes involved in organ development and programmed cell death. For this work, Brenner, Sulston, and Horvitz were awarded the Nobel Prize in Physiology or Medicine in 2002. C.elegans have become important to the study of embryogenesis, morphogenesis, development, nerve function, behavior and aging, and genetics. The C.elegans genome has been completely se- quenced and several thousand genetic mutants are available for study. This allows scientists to cor- relate changes at the DNA level with changes in phenotype. Notably, by comparing DNA sequences, it was determined that over 35% of worm genes have human homologs. Many of these genes are important for human health and development.
pharynx
gonad arm
intestine
muscle
C.elegans is a free-living, non-parasitic nematode that lives in temperate soil, where it feeds on microbes that are found in decay- ing organic matter. Adult worms measure approxi- mately one millimeter (mm)
uterus
ventral nerve cord
rectum
vulva spermatheca
Figure 1: C.elegans anatomy
in length. The outer cuticle of C.elegans is transparent, making it easy to visualize growth and development of internal structures like the pharynx, the intestine, the gonads and the muscles (Figure 1). The worm also has an extensive nervous system – in fact, the nervous system comprises almost 1/3 of the worm’s 959 somatic cells! This makes C.elegans a valuable model system for neu- roscientists (Figure 2). 2
Figure 2: Neural anatomy of C.elegans . Source: OpenWorm proj- ect. Shared under an MIT License.
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