Eukaryotes Genomes - DANIO RERIO

Zebrafish, Danio rerio, are freshwater fish that were originally found in slow streams and rice paddies and in the Ganges River in East India and Burma. They are usually black and silver in colour.

The zebrafish, Danio rerio, has become another popular "model" organism with which to study fundamental biological questions. Some of its advantages for biologists are that it is a small 1-1.5 inches freshwater fish that grows easily in aquaria. It breeds quickly and often (daily), it is a vertebrate and thus can provide clues to human biology that invertebrates may not. Its embryos, like those of most fishes, develop outside the body where they can be easily observed and are transparent so defects in development can be seen easily. Individual cells in the embryo can be labelled with a fluorescent dye and their fate followed. Embryonic development is quick (they hatch is two days). They can absorb small molecules, such as mutagens from the aquarium water. Individual cells, or clusters of cells, can be transplanted to other locations in the embryo. They can be forced to develop by parthenogenesis (in parthenogenesis (virgin birth), the females produce eggs, but these develop into young without ever being fertilised) to produce at will homozygous animals with either a male-derived or female-derived genome. They can be cloned from somatic cells and they can be made transgenic (A transgenic animal is one that carries a foreign gene that has been deliberately inserted into its genome).

Since zebrafish research began, these embryos have become very popular worldwide as a means of understanding how not only fish, but all vertebrates including humans, develop from the moment that sperm fertilizes an egg. The eggs are clear and develop outside of the mother's body, allowing scientists to watch a zebrafish egg grow into a newly formed fish under a microscope. The cells are observed while they divide and form different parts of the baby fish's body. In the development span of 2-4 days, some cells form to make the eyes, others, the heart, the liver, the stomach, the skin, the fins, etc. until the fish is complete. Scientists will occasionally move a cell to another spot to see if it will still go on to form the same part of the body as it is known to do in other embryos or if it will do something different. Occasionally a cell is removed or destroyed to see what the result is to the fish once it has developed. This is how scientists are discovering the causes of birth defects in human children and it's how they are trying to find a way to prevent these birth defects by understanding why they happen and what original cells are involved.

Work on this organism will complement that on the mouse, which is the most widely used mammalian genetic model organism. Being a vertebrate, the zebrafish ( Danio rerio) has blood, kidney and optical systems that share many features of the human systems.

Other than being a model organism in developmental biology, zebrafish may also be able to asssist scientists in environmental cleanup. Zebrafish have been bred that can detect water pollutants by glowing a certain colour. To create such radiant fish, biologists extracted fluorescent genes from jellyfish and injected them into zebrafish eggs. In the presence of certain substances, such as heavy metals, toxins or other pollutants for which the colour has been specifically aimed, the fish glow red or green. Although only those two colours have been produced so far, researchers can add up to five colors to a zebrafish, a different color for each given pollutant.

Danio rerio may also be referred to as Brachydanio rerio in older scientific literature.

References:

http://www.sanger.ac.uk/Projects/D_rerio/
http://www.fishbase.org/Summary/SpeciesSummary.cfm?genusname=Danio&speciesname=rerio
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/Z/Zebrafish.html
http://www.neuro.uoregon.edu/k12/zfk12.html