Caenorhabditis elegans, model nematode

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Taxonomy

cellular organisms - Eukaryota - Fungi/Metazoa group - Metazoa - Eumetazoa - Bilateria - Pseudocoelomata - Nematoda - Chromadorea - Rhabditida - Rhabditoidea - Rhabditidae - Peloderinae - Caenorhabditis - Caenorhabditis elegans

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Brief facts

• Caenorhabditis elegans is a free-living nematode, about 1 mm in length. In the wild, this species live in soil feeding on bacteria that grow on decaying vegetal matter. Recent studies suggested that these tiny worms may spend some time above grounds, hitching a ride on insects. The nematodes exhibit strong avoidance of UV light mediated by novel UV light receptor that is related to a large family of gustatory receptors found in insects. The N2 strain, originally isolated from mushroom compost, has been used by laboratories around the world as the wild-type C. elegans for several decades.
• Similar to other nematodes, C. elegans has an unsegmented, cylindrical body shape that is tapered at the ends. Body of typical nematode consists of an outer tube and an inner tube separated from each other by the pseudocoelomic space. The outer tube (body wall) consists of cuticle, hypodermis, excretory system, neurons and muscles, and the inner tube contains the pharynx, intestine and, in the adult, gonad.
• Caenorhabditis elegans is used extensively as a model organism since 1974 and it became first organism which genome was completely sequenced.
• Predominant sex form of the species is hermaphrodite. Pure male worms constitute about 0.05% of the total population.

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Developmental stages (life cycle)

Life Cycle Stages

The nematode's life cycle, from a single-cell egg to an adult, takes about 2 1/2 days at 25°C, and 6 days  at 15°C. The total life-span of a worm under the best growth conditions is about 12 to 18 days at 20°C. 

C. elegans reproduces predominantly as a self-fertilizing hermaphrodite. Males arise sponteneously at a frequency of 0.1% in hermaphrodite populations by meiotic nondisjunction of the X chromosome, creating XO males that can be propagated by mating with hermaphrodites.

• egg
  • unfertilized egg
  • fertilized egg egg is laid after being fertilized  inside the mother and takes about 15 hours to develop; the worms are self- and cross- fertile; pattern of embryonic development is invariable from worm to worm; every one of the 556 cells that make up the newly-hatched larva develops from a rigid pattern of mitotic division leading back to the zygote
• hatching
• larval MeSH each larval stage looks similar to the adult, only smaller
  • L1 larva
  • molting
  • L2 larva
  • molting
  • L3 larva
  • molting
  • L4 larva hermaphrodites produce sperm during the L4 stage
  • 4^th molting
• Dauer larva a developmentally arrested dispersal stage that may be formed under conditions of starvation or overcrowding
• adult

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Appendix 1: phenotypes analyzed in C. elegans

Kwok TC, Hui K, Kostelecki W, Ricker N, Selman G, Feng ZP, Roy PJ. A genetic screen for dihydropyridine (DHP)-resistant worms reveals new residues required for DHP-blockage of mammalian calcium channels. PLoS Biol. 2008 Nov 18;6(11):e278.

Comparisons of the phenotypes analyzed in C. elegans. (A) An N2 adult showing wild-type length and number of embryos (arrow). (B) An egl-19(tr89) adult is approximately wild-type in length and contains fewer embryos (arrow). (C) A him-5(e1490) adult male showing wild-type tail morphology with the spicules in the normal retracted position (arrowhead). (D) An egl-19(tr89) adult male often has spicules that are constantly protracted (arrowhead). All pictures are of animals raised on 0.33% DMSO as L4s. Scale bars, 50 µm.

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Appendix 2: C. elegans body length mutants

Mörck C, Pilon M. C. elegans feeding defective mutants have shorter body lengths and increased autophagy. BMC Dev Biol. 2006 Aug 3;6:39.

Photographs of N2, dbl-1, pha-2 and dbl-1;pha-2 representative animals. Note that while the pha-2 and dbl-1 animals are of approximately the same length, the pha-2 is comparatively thinner. Note also that the double mutant is remarkably short and with a body width similar to that of the pha-2 single mutant. All worms were developmentally age-matched to 48 hours post L4 stage.

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References

• Gems D, Riddle DL. Defining wild-type life span in Caenorhabditis elegans. J Gerontol A Biol Sci Med Sci. 2000.
• Edwards SL et al. A novel molecular solution for ultraviolet light detection in Caenorhabditis elegans. PLoS Biol. 2008 Aug 5;6(8):e198. (also cover image credit)
• Major topic: Caenorhabditis elegans (free full text articles in PubMed)

Websites

• Wikipedia: Caenorhabditis elegans

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