Caenorhabditis elegans

Caenorhabditis elegans is a species of parasitic roundworm in the Nematoda phylum. It can be found in temperate regions, in many different areas of the world. It prefers to reside in nutrient rich soils. Its scientific name is derived from the Greek terms Caeno, meaning recent, rhabditis, meaning rod-like, and the Latin term elegans, which means elegant. It was first named by Maupas in 1900, but was not classified in the Caenorhabditis subgenus until 1952 by Osche.

Caenorhabditis elegans is a non-segmented worm that shares many features of other species of worms, including intestines, a mouth, gonads, a pharynx, and collagenous cuticles. Although this species holds both male and hermaphroditic individuals, males only comprise .05 percent of the entire population. Males have unique anatomical features including vas deferens, a single-lobed gonad, and a tail that is specialized for breeding. Hermaphroditic individuals have one uterus, two ovaries, a spermatheca, and oviducts.

Caenorhabditis elegans eggs are laid by hermaphrodites, and will develop through four stages of juvenile life as larvae. If second stage larvae reside in an area where food is not abundant, they are able to develop into a third stage form known as dauer state. In this stage, the larvae become dormant and do not develop into stage four larvae. Hermaphrodites can produce sperm in their stage four form as well as oocytes. Both the sperm and oocytes are stored in the same region of the gonad until a sperm is forced into the spermatheca by an oocyte. The spermatheca also holds sperm and oocytes and is where insemination of the oocytes occurs. Males can inseminate hermaphrodites, resulting in about three hundred eggs, but when wild hermaphroditic individuals self-inseminate, it results in over a thousand eggs.

The diet of Caenorhabditis elegans consists of bacteria found in decaying matter in the wild. It lives in this matter, but not much is known about its habits. Most individuals in laboratories were taken from areas associated with humans like gardens or compost piles, as well as rotting fruit. In the wild, it has been found to travel on invertebrates like millipedes, gastropods, isopods, and insects and in laboratory settings, it has been found to feed off these hosts if they die.

Caenorhabditis elegans is known for its uses in laboratories, where it is now used as a model organism. This research began in 1974, when Sydney Brenner studied its capacities for growth. During these studies, Brenner noted its use in genetic studies and chose the species because of its natural availability. This species is also convenient for study because it is transparent, making it easy to study internally and it is easily stored for long periods. Storage is most effective if starving young are placed in liquid nitrogen or stored at a temperature of −80°C. Genetic related studies of this species include aging research, cell growth and death rates, RNA interference studies, and meiosis studies. Its nervous system has also been extensively researched, with studies focusing on male breeding habits, thermotaxis, mechanotransduction, and chemotaxis.

In 1998, it was announced that the entire genome of Caenorhabditis elegans had been sequenced, making this multicellular organism the first of its kind to have a completed genome sequence. However, it was not until 2002 that the remaining gaps in the original sequencing were cleared up. The sequence has about 100 million base pairs and has around 20,470 protein-coding genes. However, the sequencing of genomes is not a precise science and so completed genomes are often subject to change. In 2006, the number of recorded RNA genes in this species rose from 1,300 in 2005 to 16,000, due to the discovery of a new class of 21U-RNA genes. In 2008, the WS197 added over 4,600 base pairs to the original sequence and two more base pairs were added by the WS202 release of WormBase in 2009. These types of changes are typically minor, with the reduction or addition of only a few base pairs.

Although the genome sequence of Caenorhabditis elegans is complete, researchers are still studying the sequences of other species within its genus, like C. japonica, C. brenneri, and C. remanei. The sequence of the related species C. briggsae was completed in 2003, making it possible to compare the two species genetically.

Caenorhabditis elegans has been used in space related research, making news when it was reported to have survived the Space Shuttle Columbia disaster in 2003. In 2009, it was announced that descendants of the worms from the Columbia shuttle crash would be sent into space to spend two weeks on the International Space Station. The worms would be studied for the effects of zero gravity on muscle physiology and development, although the main research would focus on the genetic signs of muscle atrophy.

Because of their important genetic research on Caenorhabditis elegans and how it benefited the medical world, Sydney Brenner, John Sulston, and H. Robert Horvitz were all awarded the Nobel Prize in Physiology or Medicine in 2002. This prize also went to Craig C. Mello and Andrew Fire in 2006 for their studies regarding RNA interference in this species. Additionally, the Nobel Prize in Chemistry was given to Martin Chalfie in 2008 for his research in green fluorescent proteins within the worm. The WormBase database documents the close relationships between Brenner and his colleagues as well as the information about their studies and findings regarding Caenorhabditis elegans.

Image Caption: Caenorhabditis elegans. Credit: Kbradnam/Wikipedia (CC BY-SA 2.5)