Model organisms are non-human species that we use to study biological phenomena that are recapitulated in humans. Lab mice (Mus musculus), fruit flies (Drosophila melanogaster), and the bacterium E. coli all have long histories in scientific experimentation as model organisms. In the early 1960s, another model organism was catapulted to the forefront of biology: the soil-dwelling nematode C. elegans, a microscopic, invertebrate worm.
Much of what we know about C. elegans was originally researched by Sydney Brenner. As a cold and starving Oxford graduate student, the young Brenner drove to Cambridge to be among the first to glimpse Watson and Crick’s double helix model of DNA, a trip that would change his life. Inspired after witnessing the birth of molecular biology firsthand, Brenner spent the following decade deciphering the genetic code with his colleagues, together revealing the existence of messenger RNA (mRNA) and triplet mRNA codons. By 1963, the 36-year-old genetic biologist already had a lifetime’s worth of scientific accomplishments under his belt. Not content to rest on his laurels, he turned his attention to a new problem: applying genetics to elucidate the development of the nervous system.
Figure 1: An artfully-shot photograph of Sydney Brenner from the AKG Science Photo Library
Brenner already knew from his previous research experience that the commonly-used animal models of the day would be ineffective for his neurobiology studies. For one, they had too many neurons to work with in a feasible way. The brain of even the humble fruit fly contains over 100,000 neurons. The mouse brain contains roughly 1000 times as many neurons as the fly, and the human brain roughly 1000 times as many as that! For another, other animal models were simply too large to fit in the field of view of a transmission electron microscope, an instrument critical to the study of individual neurons. These two shortcomings of contemporary model organisms led Brenner to searching for his ideal animal model, one that would contain only a few hundred neurons in its nervous system and grow no longer than a millimeter in length.
In addition to his neurobiology-related needs for this notional model organism, he sought an organism with a short life cycle, a large brood size, and the ability to thrive in a laboratory environment, all generally useful traits to facilitate maintenance of the animal. Brenner’s experience with genetic experiments led also to a requirement that the model have relatively simple anatomy with cells that could be easily identified and whose lineages could be traced. Based on these criteria, the search for a new model organism quickly narrowed to microscopic worms known as nematodes; from there, he settled on C. elegans, a tiny non-hazardous organism found abundantly within soil and rotting vegetable matter.
A key reason for this choice was the ease of genetic manipulation within C. elegans, which exists in two different sexual phenotypes: males and self-fertilizing hermaphrodites. Hermaphrodites are essentially females that can temporarily produce and store sperm, and then produce oocytes (unfertilized eggs) that are fertilized by the stored sperm. The vast majority of these offspring will themselves be hermaphrodites, with less than 0.2% being true males. Thus, an entire population can be grown from just a single organism, and since all offspring must contain the genes from the single parent, mutants are far easier to detect and manage.
Figure 2: The benefits of C. elegans as a model organism (image from Wikimedia)
Brenner received the 2002 Nobel Prize in Physiology for his work in establishing C. elegans as an experimental model. This award was shared with scientists John Sulston and Robert Horvitz, who used C. elegans as a means to uncover the genetic regulation of programmed cell death. In his Nobel lecture, which he titled “Nature’s Gift to Science,” Brenner recounted the journey of C. elegans from being considered a “joke organism” to becoming one of the most powerful experimental systems in use today.
C. elegans must have clearly acquired a taste for the spotlight, since it returned to the Nobel stage 6 years later for its role in the discovery of RNA interference. This nematode continues to be used in an ever-growing variety of research applications, serving as a model for neurodegenerative diseases, a window into the mechanisms of aging, one of the easiest whole organism models for understanding the effects of genetic diversity on phenotypes, and a means for toxicology screening to ensure the safety of the chemicals we use daily. After over half a century of use, C. elegans continues to prove that it truly is nature’s gift to science.