model organism

A model organism is a species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workings of other organisms. This is possible because fundamental biological principles such as metabolic, regulatory, and developmental pathways, and the genes that code for them, are conserved through evolution. There are many model organisms. The first model organism for molecular biology was probably the bacterium Escherichia coli which is common in the human digestive system (and usually beneficial -- the dangerous is a rare strain). This also led to a study of many bacteriophages, particularly phage lambda. In eukaryotes, several yeasts, particularly Saccharomyces cerevisiae ("baker's" or "budding" yeast), have been widely studied, largely because they are quick and easy to grow. The cell cycle in a simple yeast is very similar to the cell cycle in humans, and regulated by homologous proteins. The fruit fly Drosophila melanogaster was studied, again because it was easy to grow for a multicellular organism. The roundworm Caenorhabditis elegans is studied because it has very defined development patterns and can be rapidly assayed for abnormalities. When researchers look for an organism to use in their studies, they look for several traits. Common among these are size, generation time, accessibility, manipulation, genetics, conservation of mechanisms, and potential economic benefit. As comparative molecular biology has become more common, some researchers have sought model organisms that represent assorted lineages of life.

Important model organisms

Viruses

lambda phage

Prokaryotes

Escherichia coli (E. coli)
Bacillus subtilis
Mycoplasma genitalium - a minimal organism
Vibrio fischeri - quorum sensing, bioluminescence and animal-bacterial symbiosis with Hawaiian bobtail squid
Synechocystis, a photosynthetic cyanobacteria widely used in photosynthesis research.

Unicellular eukaryotes

Saccharomyces cerevisiae - baker's yeast or budding yeast (used in brewing and baking)
Schizosaccharomyces pombe - fission yeast
Neurospora crassa - red bread mold
Chlamydomonas reinhardtii- a unicellular green alga used in photosynthesis research.
Tetrahymena thermophila - a free living freshwater ciliated protozoan

Multicellular eukaryotes

Plants

Arabidopsis thaliana, a plant, usually called Arabidopsis

Lotus japonicus a model legume plant.

Medicago truncatula a model legume.

Rice is used as a model for cereal biology.

Fungi

Aspergillus nidulans, subject of genetics studies

Invertebrates

Arbacia punctulata, the purple-spined sea urchin, classical subject of embryological studies

Caenorhabditis elegans, a nematode, usually called C. elegans

Euprymna scolopes, the Hawaiian bobtail squid, model for animal-bacterial symbiosis, bioluminescent vibrios.

Drosophila, usually the species Drosophila melanogaster - a kind of fruit fly, famous as the subject of genetics experiments by Thomas Hunt Morgan and others. Easily raised in lab, rapid generations, mutations easily induced, many observable mutations.

Loligo pealei, a squid, subject of studies of nerve function because of its giant axon (nearly 1 mm diameter, roughly a thousand times larger than typical mammalian axons)

Vertebrates

Cavius porcellus, the guinea pig, used by Robert Koch and other early bacteriologists as a host for bacterial infections, hence a byword for "laboratory animal" even though rarely used today.

Rat (Rattus norvegicus) - particularly useful as a toxicology model; also particularly useful as a neurological model and source of primary cell cultures, owing to the larger size of organs and suborganellar structures relative to the mouse.

Mouse (Mus musculus) - the classic model vertebrate

Zebrafish (Brachydanio rerio), a freshwater fish, has a nearly transparent body which provides unique visual access to the animal's internal anatomy throughout its life. Zebrafish are used to study development, toxicology and toxicopathology, specific gene function and roles of signaling pathways.

Xenopus laevis, the African clawed toad, also used in development

Takifugu rubipres, a pufferfish - has a small genome with little junk DNA

Dog (Canis lupus familiaris) - an important respiratory and cardiovascular model

Homo sapiens, human beings, which are capable of self-reporting and have the largest catalog of known genetic disorders

References

  Spitsbergen J.M. and Kent M.L. (2003). The state of the art of the zebrafish model for toxicology and toxicologic pathology research--advantages and current limitations. Toxicol Pathol. 31 (Supplement), 62-87.  PubMed Abstract Link => PMID 12597434.  Riddle, Donald L.; Blumenthal, Thomas; Meyer, Barbara J.; and Priess, James R. (Eds.). (1997).  C. ELEGANS II.  Woodbury, NY: Cold Spring Harbor Press.  ISBN 0-87969-532-3.  Full text available on-line.