Caenorhabditis elegans

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Caenorhabditis elegans
Scientific classification
Kingdom: Animalia Phylum: Nematoda Class: Secernentea Order: Rhabditida Family: Rhabditidae Genus: Caenorhabdtis Species: C.elegans
Binomial name
Caenorhabdtis elegans Maupas 1900

Description and significance

Caenorhabditis elegans is a simple organism that is small free living nematode. It is found in various parts of the world. A microscope is required to view a C. elegans because its length ranges up to 1 mm. The growth of C. elegans is rapid; under a standard laboratory condition it takes the entire life cycle from egg to an adult producing more eggs in just 3.5 days at 20°C. After the egg hatches, it undergoes four larval stages L1 to L4; the larval stages are punctuated by molts.² After the L4 stage the C. elegans will undergo a final molt to produce an adult. It is an adult stage that its length is 1mm. At a time when there is a food shortage and a high population, the C. elegans take an alternative pathway during the larval stages. At the alternative stage a dauer is formed after the molt of L2 instead of a L3. The dauer is able to survive these conditions by not feeding and is resistant to desiccation.² The dauer stage is able to survive for several months without further developing; when there is change in the environment such as a availability of food the C. elegans will molt to the normal L4 stage. C. elegans lives for about 18- 23 days. There are two types of sexes which are hermaphrodites and males; its appearance is visually different at the adult stage. The male only produces sperm, in order to reproduce it must mate with a hermaphrodite. This cross fertilization produces both the males and hermaphrodites in a 1:1 proportion. The hermaphrodites are able to produce both sperm and oocytes and undergo self-fertilization. During the self-fertilization it produces hermaphrodites and males arise spontaneously at an extremely low frequency.

The C. elegans are part of the model system. The key attributes of C. elegans as an experimental system for biological systems are its simplicity, transparency, ease of cultivation in the laboratory, short life cycle, suitability of genetic analysis and small genome size.² Its biological mechanisms are similar to majority of the animal species that allows an ideal model system.

Genome structure

The genes control all the functions and proper developments of the C.elegans. It is one of the first multicellular organisms that have the entire genome sequenced. The C. elegans has a small genome, yet a very complex one. It has over 19,000 protein coding genes. There are 8 x 107 base pairs of DNA in the genome.³ In the genome there are many mutable loci; that allow observing the genetic defects easier therefore making it an model organism. The C.elegans cells are diploid. Both the hermaphrodites and males have five autosomes; the only difference being that the hermaphrodites have one pair X chromsomes while the male has one X chromosome.

Cell structure and metabolism

The C.elegans have an simple anatomy. The c. elegans exterior contains an pseudocoelem, which also causes an separation along the body wall and the gut. The body wall contains cells called hypodermal that secretes collagenous cuticle along the body wall that covers the surface. There are also many muscle cells beneath the body wall. Both the hermaphrodites and the male have an similar anatomy, the differences would be that the males are thinner, shorter and contain a cloaca that is ventral to the posterior end. The anterior contains a tip of the head that contains a mouth. Then there is the gut which contains a pharynx and intestine. The intestine is long that starts from the mouth and ends at the intestine. There is an anus located at the posterior end of the worm. The c. elegans have a simple nervous system, there are many nerves connected to the muscles that generates simple movements.

The male and hermaphrodites differ in the arrangement of the gonad and in the tail. The hermaphrodite has two symmetrical lobes with one single opening in the uterus. The fertilization occurs in the spermatheca. The location of the spermatheca is between the uterine and vulvae ¹. There are specific muscle cells that are responsible for egg laying in the hermaphrodite. In the male gonad there is a one simple tube opening at the cloaca. The tails of the two sexes are different; the male tail is structurally different with complex musculature and nerves required for mating.

The osmoregulation is regulated by the excretory system. This system consists of the excretory duct cell, excretory pore cell, excretory gland cell, and excretory cells ¹. The excretory cell is the largest cell in the c. elegan which reaches the tip of the head to tail. The secretory system regulates the secretion of the glycoproteins which is responsible to make up the replenishable surface coat over the epicuticle. ³

The C. elegan molts four times during each of the larval stages. The molting is not required for growth in the c. elegans. It seems that the molting cycle activates the developmental cues controlling postembryonic cell lineages, and even in the development plasticity in cell morphology and function. ³.

Ecology

C. elegans lives in the soil across most of the temperate regions of the world. In order to reproduce and grow it requires an humid environment, ambient temperature and atmospheric oxygen. C. elegan feeds on diverse microorganism one such example would be bacteria.

In the laboratory it is easily maintained. Its food source in the lab would be e. coli. The C. elegans are grown on agar plates or in a liquid culture.

Application to Biotechnology

There are many advantages that allow it to be applied to biotechnology such as the rapid life cycle, ability to be easily cultivated in the laboratory, its small genome size, and the genetic analysis can be applied. Due to its usefulness in the lab it allows research to be done that answers variety of the problems in animal biology.

The C. elegans mutants allow a better understanding of the development and behavior of many animals. The genome of the C. elegans makes direct connections to many vertebrates. There is a degree of similarity between the genome of the human and the C. elegans; that allows a better understanding and improvement of the human biology. It is found that from 84 human disease genes that have been cloned 25 have direct orthologues in the C. elegans genome and a further 43 have a considerable similarity with nematode genes. It also has significant impact on the medicine and agriculture fields by being a model organism for many studies of the parasitic nermatodes. The nervous system of the C. elegans is simple therefore allowing research opportunities for function and development in other animals.

References

2. Wood William Barry; ed. The Nematode Caenorhabditis Elegans.New York: Cold Spring Harbor Laboratory, 1988.

3.Riddle Donald, Blumenthal Thomas, Meyer Barbara, Priess James eds. C. elegans II. New York: Cold Spring Harbor Laboratory, 1997.

4. Melendez Alicia, Talloczy Zsolt, Seaman Matthew, Eskelinen Eeva-Liisa, Hall H. David, Levine Beth. "Autophagy Genes are Essential for Dauer Development and Life Span Extension in C.elegans" www.science.org SCIENCE VOL 301. September 2003.

5. Yang Zhao, Johnsen Robert, David Baille, Ann Rose. Worms in Space? A Model Biological Desimeter. Gravitional and Space Biology 18(2). June 2005.