On Air

Investment

Buy this Domain?
Do you interesting about this domain and the running project?
Feel free to send your offer to webmaster.
pay with Paypal

Advertising

Caenorhabditis elegans

| subdivision_ranks = Subspecies | subdivision =
  • Caenorhabditis elegans var. BergeracLes modalités de la reproduction et le déterminisme du sexe chez quelques nematodes libres. Nigon V. Ann. Sci. Nat. Zool. Biol. Anim. 1949;11:1–132. (for instance strain BO)
  • Caenorhabditis elegans var. BristolTc1 transposition and mutator activity in a Bristol strain of Caenorhabditis elegans. Babity JM, Starr TV and Rose AM, Mol Gen Genet., 1990 June, 222(1), pages 65-70, (for instance strain N2)Structural analysis of Tc1 elements in Caenorhabditis elegans var. Bristol (strain N2). Harris LJ and Rose AM, Plasmid. 1989 Jul;22(1), page 10-21,
}} Caenorhabditis elegans (}}) is a free-living (not parasitic), transparent nematode (roundworm), about 1 mm in length, C. elegans is an unsegmented pseudocoelomate, and lacks a respiratory and a circulatory system. It possesses gut granules which emit a brilliant blue fluorescence, a wave of which is seen at death in a 'death fluorescence'. The majority of these nematodes are hermaphrodites. Males have specialised tails for mating that include spicules. In 1963, Sydney Brenner proposed research into C. elegans primarily in the area of neuronal development. In 1974, he began research into the molecular and developmental biology of C. elegans, which has since been extensively used as a model organism. C. elegans was the first multicellular organism to have its whole genome sequenced, and as of 2012, the only organism to have its connectome (neuronal "wiring diagram") completed. It is the type species of its genus.

Anatomy

C. elegans is unsegmented, , and bilaterally symmetrical. It has a cuticle (a tough outer covering, as an exoskeleton), four main epidermal cords, and a fluid-filled pseudocoelom (body cavity). It also has some of the same organ systems as larger animals. About one in a thousand individuals is male and the rest are hermaphrodites. The pharynx is a muscular food pump in the head of C. elegans, which is triangular in cross-section. This grinds food and transports it directly to the intestine. A set of "valve cells" connects the pharynx to the intestine, but how this valve operates is not understood. After digestion, the contents of the intestine are released via the rectum, as is the case with all other nematodes. No direct connection exists between the pharynx and the excretory canal, which functions in the release of liquid urine. Males have a single-lobed gonad, a vas deferens, and a tail specialized for mating, which incorporates spicules. Hermaphrodites have two ovaries, oviducts, spermatheca, and a single uterus.

Microanatomy - gut granules

Numerous gut granules are present in the intestine of C. elegans, the functions of which are still not fully known, as are many other aspects of this nematode, despite the many years that it has been studied. These gut granules are found in all of the Rhabditida orders. They are very similar to lysosomes in that they feature an acidic interior and the capacity for endocytosis, but they are considerably larger, reinforcing the view of their being storage organelles. A remarkable feature of the granules is that when they are observed under ultraviolet light, they react by emitting an intense blue fluorescence. Another phenomenon seen is termed 'death fluorescence'. As the worms die, a dramatic burst of blue fluorescence is emitted. This death fluorescence typically takes place in an anterior to posterior wave that moves along the intestine, and is seen in both young and old worms, whether subjected to lethal injury or peacefully dying of old age. Many theories have been posited on the functions of the gut granules, with earlier ones being eliminated by later findings. They are thought to store zinc as one of their functions. Recent chemical analysis has identified the blue fluorescent material they contain as a glycosylated form of anthranilic acid (AA). The need for the large amounts of AA the many gut granules contain is questioned. One possibility is that the AA is antibacterial and used in defense against invading pathogens. Another possibility is that the granules provide photoprotection: the bursts of AA fluorescence entail the conversion of damaging UV light to relatively harmless visible light. This is seen a possible link to the melanin–containing melanosomes.

Reproduction and development

All cells of the germline arise from a single primordial germ cell, called the P4 cell established early in embryogenesis.Kimble J, Crittenden SL. Germline proliferation and its control. 2005 Aug 15. In: WormBook: The Online Review of C. elegans Biology Internet. Pasadena (CA): WormBook; 2005-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK19769/ This germ cell divides to generate two further germ cells and these do not divide further until after hatching. The hermaphrodite, which is considered to be a specialized form of self-fertile female because its soma is female whereas its germline produces male gametes first, lays eggs through its uterus after internal fertilization. Under environmental conditions which are favourable for reproduction, hatched larvae develop through four stages or molts, designated as L1 to L4. When conditions are stressed as in food insufficiency, C. elegans can enter an alternative third larval stage called the dauer stage. Dauer is German for permanent. Dauer larvae are stress-resistant; they are thin and their mouths are sealed and cannot take in food, and they can remain in this stage for a few months. Hermaphrodites produce all their sperm in the L4 stage (150 sperm per gonadal arm) and then produce only oocytes. The sperm cells are stored in the same area of the gonad as the oocytes until the first oocyte pushes the sperm into the spermatheca (a chamber wherein the oocytes become fertilized by the sperm). The male can inseminate the hermaphrodite, which will preferentially use male sperm (both types of sperm are stored in the spermatheca). The sperm of C. elegans is amoeboid, lacking flagella and acrosomes. When self-inseminated, the wild-type worm will lay about 300 eggs. When inseminated by a male, the number of progeny can exceed 1,000. At 20 °C, the laboratory strain of C. elegans (N2) has an average lifespan around 2–3 weeks and a generation time around 4 days. Nematodes have a fixed, genetically determined number of cells, a phenomenon known as eutely. The male C. elegans has 1031 cells, a number which does not change after cell division ceases at the end of the larval period. Growth is solely due to an increase in the size of individual cells. C. elegans has five pairs of autosomes and one pair of sex chromosomes. Sex in C. elegans is based on an X0 sex-determination system. Hermaphrodites of C. elegans have a matched pair of sex chromosomes (XX); the rare males have only one sex chromosome (X0).

Ecology

The different Caenorhabditis species occupy various nutrient- and bacteria-rich environments. They feed on the bacteria that develop in decaying organic matter. Soil lacks enough organic matter to support self-sustaining populations. C. elegans can survive on a diet of a variety of many kinds of bacteria, but its wild ecology is largely unknown. Most laboratory strains were taken from artificial environments such as gardens and compost piles. More recently, C. elegans has been found to thrive in other kinds of organic matter, particularly rotting fruit. Invertebrates such as millipedes, insects, isopods, and gastropods can transport dauer larvae to various suitable locations. The larvae have also been seen to feed on their hosts when they die. Nematodes can survive desiccation, and in C. elegans, the mechanism for this capability has been demonstrated to be late embryogenesis abundant proteins. C. elegans, as other nematodes, can be eaten by predator nematodes and other omnivores, including some insects.Elaine R. Ingham Soil biology primer USDA The Orsay virus is a virus that affects C. elegans. ; Interactions with fungi Wild isolates of Caenorhabditis elegans are regularly found with infections by Microsporidia fungi. One such species, Nematocida parisii, replicates in the intestines of C. elegans. Arthrobotrys oligospora is the model organism for interactions between fungi and nematodes.Niu, Xue-Mei; Zhang, Ke-Qin (2011). "Arthrobotrys oligospora a model organism for understanding the interaction between fungi and nematodes". Mycology. 2 (2): 59–78. It is the most common nematode capturing fungus, and most widespread nematode trapping fungus in nature.

Research use

In 1963, Sydney Brenner proposed using C. elegans as a model organism for the investigation primarily of neural development in animals. It is one of the simplest organisms with a nervous system. The neurons do not fire action potentials, and do not express any voltage-gated ion channels. In the hermaphrodite, this system comprises 302 neurons the pattern of which has been comprehensively mapped, in what is known as a connectome, and shown to be a small-world network. Research has explored the neural and molecular mechanisms that control several behaviors of C. elegans, including chemotaxis, thermotaxis, mechanotransduction, learning, memory, and mating behaviour. Brenner also chose it as it is easy to grow in bulk populations, and convenient for genetic analysis. Alt. URL It is a multicellular eukaryotic organism, yet is simple enough to be studied in great detail. The transparency of C. elegans facilitates the study of cellular differentiation and other developmental processes in the intact organism. The spicules in the male clearly distinguish males from females. Strains are cheap to breed and can be frozen. When subsequently thawed, they remain viable, allowing long-term storage.{{cite journal |last1=Brenner |first1=S |title=The Genetics of Caenorhabditis elegans |journal= Genetics |volume=77 |issue=1 |pages=71–94 |year=1974 |pmid=4366476 |pmc=1213120 }} Maintenance is easy when compared to other multicellular model organisms, a few hundred nematodes can be kept on a single agar plate and suitable growth medium. Brenner described the use of a mutant of E. Coli – OP50. OP50 is a uracil-requiring organism and its deficiency in the plate prevents the overgrowth of bacteria which would obscure the worms. Brenner, S. (1974). Genetics 77, 71

Notable findings

The developmental fate of every single somatic cell (959 in the adult hermaphrodite; 1031 in the adult male) has been mapped. Programmed cell death ( apoptosis) eliminates many additional cells (131 in the hermaphrodite, most of which would otherwise become neurons); this "apoptotic predictability" has contributed to the elucidation of some apoptotic genes. Cell death-promoting genes and a single cell-death inhibitor have been identified. to highlight the nuclei of all cells]] RNA interference (RNAi) is a relatively straightforward method of disrupting the function of specific genes. Silencing the function of a gene can sometimes allow a researcher to infer its possible function(s). The nematode can be soaked in, injected with, or fed with genetically transformed bacteria that express the double-stranded RNA of interest, the sequence of which complements the sequence of the gene that the researcher wishes to disable.

Genome

C. elegans was the first multicellular organism to have its whole genome sequenced. The sequence was published in 1998, Size and gene content. The C. elegans genome is about 100 million base pairs long and consists of six chromosomes and a mitochondrial genome. Its gene density is about one gene per five kilo-base pairs. Introns make up 26% and intergenic regions 47% of the genome. Many genes are arranged in clusters and how many of these are operons is unclear. C. elegans and other nematodes are among the few eukaryotes currently known to have operons; these include trypanosomes, flatworms (notably the trematode Schistosoma mansoni), and a primitive chordate tunicate Oikopleura dioica. Many more organisms are likely to be shown to have these operons.{{Cite journal |last1=Blumenthal |first1=T |year=2004 |title=Operons in eukaryotes |journal=Briefings in Functional Genomics and Proteomics |volume=3 |issue=3 |pages=199–211 |doi=10.1093/bfgp/3.3.199 |pmid=15642184 }} Protein-coding genes. The genome contains an estimated 20,470 protein-coding genes.{{cite web |date=10 August 2011 |title=WS227 Release Letter |url=http://www.wormbase.org/wiki/index.php/WS227 |publisher= WormBase |accessdate=2013-11-19 }} About 35% of C. elegans genes have human homologs. Remarkably, human genes have been shown repeatedly to replace their C. elegans homologs when introduced into C. elegans. Conversely, many C. elegans genes can function similarly to mammalian genes. The number of known RNA genes in the genome has increased greatly due to the 2006 discovery of a new class of 21U-RNA genes,{{cite journal |last1=Ruby |first1=JG |last2=Jan |first2=C |last3=Player |first3=C |last4=Axtell |first4=MJ |last5=Lee |first5=W |last6=Nusbaum |first6=C |last7=Ge |first7=H |last8=Bartel |first8=DP |year=2006 |title=Large-scale Sequencing Reveals 21U-RNAs and Additional MicroRNAs and Endogenous siRNAs in C. elegans |journal= Cell |volume=127 |issue=6 |pages=1193–207 |doi=10.1016/j.cell.2006.10.040 |pmid=17174894 }} and the genome is now believed to contain more than 16,000 RNA genes, up from as few as 1,300 in 2005.{{cite journal |last1=Stricklin |first1=SL |last2=Griffiths-Jones |first2=S |last3=Eddy |first3=SR |year=2005 |title=C. elegans noncoding RNA genes |journal= WormBook |volume= |issue= |pages= |doi=10.1895/wormbook.1.1.1 |pmc=4781554}} Scientific curators continue to appraise the set of known genes; new gene models continue to be added and incorrect ones modified or removed. The reference C. elegans genome sequence continues to change as new evidence reveals errors in the original sequencing. Most changes are minor, adding or removing only a few base pairs of DNA. For example, the WS202 release of WormBase (April 2009) added two base pairs to the genome sequence. Related genomes. In 2003, the genome sequence of the related nematode C. briggsae was also determined, allowing researchers to study the comparative genomics of these two organisms. The genome sequences of more nematodes from the same genus e.g., C. remanei, C. japonica and C. brenneri (named after Brenner), have also been studied using the shotgun sequencing technique. These sequences have now been completed.

Other genetic studies

As of 2014, C. elegans is the most basal species in the 'Elegans' group (10 species) of the 'Elegans' supergroup (17 species) in phylogenetic studies. It forms a branch of its own distinct to any other species of the group.A streamlined system for species diagnosis in Caenorhabditis (Nematoda: Rhabditidae) with name designations for 15 distinct biological species. MA Félix, C Braendle and AD Cutter, PLoS One, 2014, Tc1 transposon is a DNA transposon active in C. elegans.

Scientific community

In 2002, the Nobel Prize in Physiology or Medicine was awarded to Sydney Brenner, H. Robert Horvitz, and John Sulston for their work on the genetics of organ development and programmed cell death in C. elegans. The 2006 Nobel Prize in Physiology or Medicine was awarded to Andrew Fire and Craig C. Mello for their discovery of RNA interference in C. elegans. Many scientists who research C. elegans closely connect to Sydney Brenner, with whom almost all research in this field began in the 1970s; they have worked as either a postdoctoral or a postgraduate researcher in Brenner's lab or in the lab of someone who previously worked with Brenner. Most who worked in his lab later established their own worm research labs, thereby creating a fairly well-documented "lineage" of C. elegans scientists, which was recorded into the WormBase database in some detail at the 2003 International Worm Meeting.

See also

References

Further reading

  • {{cite book |last1=Bird |first1=J |last2=Bird |first2=AC |title=The structure of nematodes |publisher= Academic Press
|year=1991 |isbn=0-12-099651-0 |pages=1, 69–70, 152–153, 165, 224–225}}

External links

  • Brenner S (2002) Nature's Gift to Science. In. http://nobelprize.org/nobel_prizes/medicine/laureates/2002/brenner-lecture.pdf (also Horvitz and Sulston lectures)
  • WormBase – an extensive online database covering the biology and genomics of C. elegans and other nematodes
  • WormAtlas – online database on all aspects of C. elegans anatomy with detailed explanations and high-quality images
  • WormBook – online review of C. elegans biology
  • AceView WormGenes – another genome database for C. elegans, maintained at the NCBI
  • C. elegans II – a free online textbook.
  • WormWeb Neural Network – an online tool for visualizing and navigating the connectome of C. elegans
  • C. elegans movies – a visual introduction to C. elegans
  • Caenorhabditis elegans at eppo.int ( EPPO code CAEOEL)
"green air" © 2007 - Ingo Malchow, Webdesign Neustrelitz
This article based upon the http://en.wikipedia.org/wiki/Caenorhabditis_elegans, the free encyclopaedia Wikipedia and is licensed under the GNU Free Documentation License.
Further informations available on the list of authors and history: http://en.wikipedia.org/w/index.php?title=Caenorhabditis_elegans&action=history
presented by: Ingo Malchow, Mirower Bogen 22, 17235 Neustrelitz, Germany