Циона ішекшесі: биологиясы мен таралуы

Species of ascidian

Ciona intestinalis (sometimes known by the common name of vase tunicate) is an ascidian (sea squirt), a tunicate with very soft tunic. Its Latin name literally means "pillar of intestines", referring to the fact that its body is a soft, translucent column like structure, resembling a mass of intestines sprouting from a rock. It is a globally distributed cosmopolitan species. Since Linnaeus described the species, Ciona intestinalis has been used as a model invertebrate chordate in developmental biology and genomics. Studies conducted between 2005 and 2010 have shown that there are at least two, possibly four, sister species. More recently it has been shown that one of these species has already been described as Ciona robusta. By anthropogenic means, the species has invaded various parts of the world and is known as an invasive species. Although Linnaeus first categorised this species as a kind of mollusk, Alexander Kovalevsky found a tadpole like larval stage during development that shows similarity to vertebrates. Recent molecular phylogenetic studies as well as phylogenomic studies support that sea squirts are the closest invertebrate relatives of vertebrates. Its full genome has been sequenced using a specimen from Half Moon Bay in California, US, showing a very small genome size, less than 1/20 of the human genome, but having a gene corresponding to almost every family of genes in vertebrates.

Ciona intestinalis is a solitary tunicate with a cylindrical, soft, gelatinous body, up to long. The body colour and colour at the distal end of siphons are major external characters distinguishing sister species within the species complex. The body of Ciona is bag like and covered by a tunic, which is a secretion of the epidermal cells. The body is attached by a permanent base located at the posterior end, while the opposite extremity has two openings, the buccal and atrial siphons. Water is drawn into the ascidian through the buccal (oral) siphon and leaves the atrium through the atrial siphon (cloacal).

Ciona intestinalis is a hermaphroditic broadcast spawner but cannot self fertilize. Eggs and sperm, when released, can stay in the water column for 1 to 2 days, while the larvae are free swimming for 2 to 10 days. Ciona intestinalis is considered to be an invasive species and grows in dense aggregations on any floating or submerged substrate, particularly artificial structures like pilings, aquaculture gear, floats and boat hulls, in the lower intertidal to sub tidal zones. It often grows with or on other fouling organisms. It is thought to spread to new areas mainly through hull fouling. Since its larvae can live for up to 10 days, this species may also be transferred through the release of bilge or ballast water. The potential impact of C. intestinalis and its introduction to new habitats can be avoided, so most agencies suggest that fish and shellfish harvesters are to avoid transfer of harvested shellfish and fishing gear to other areas, and to dry gear thoroughly before transfer, along with inspecting boat hulls. They also recommend that, if necessary, to clean them thoroughly, and to disinfect with bleach or vinegar and dry them before moving to other areas. Agencies also recommended the disposal of any organisms removed from boat hulls or gear on land and to release bilge water on land or disinfect it.

Ciona intestinalis is an hermaphrodite that releases sperm and eggs into the surrounding seawater almost simultaneously. C. intestinalis is self sterile, and thus has been used for studies on the mechanism of self incompatibility. Self/non self recognition molecules are considered to play a key role in the process of interaction between sperm and the vitelline coat of the egg. It appears that self/non self recognition in ascidians such as C. intestinalis is mechanistically similar to self incompatibility systems in flowering plants.

In the sea squirt C. intestinalis a CB1 and CB2 type cannabinoid receptors is found to be targeted to axons, indicative of an ancient role for cannabinoid receptors as axonal regulators of neuronal signalling.

Ciona intestinalis was one of the first animals to have its full genome sequenced, in 2002. It has a relatively small genome (about 160 Mbp) consisting of 14 pairs of chromosomes with about 16,000 genes.

The draft genome analysis identified nine Hox genes, which are Ci Hox1, 2, 3, 4, 5, 6, 10, 12, and 13.

A majority of genetically encoded voltage indicator are based on the C. intestinalis voltage sensitive domain (Ci VSD).

There is one transferrin ortholog which is divergent from those of vertebrate models, and even more divergent from non chordates.

A retinol dehydrogenase CiRdh10 is disclosed in Belyaeva et al. 2015.