| Chilodonella uncinata | |
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| Species: | C. uncinata |
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| Chilodonella uncinata (Ehrenberg, 1838)[1] | |
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Chilodonella uncinata is asingle-celled organism of theciliate class ofalveolates. As aciliate,C. uncinata hascilia covering its body and a dual nuclear structure, themicronucleus andmacronucleus.[2][3][4][5] Unlike some other ciliates,C. uncinata contains millions ofminichromosomes (somatic chromosomes) in its macronucleus while its micronucleus is estimated to contain 3chromosomes.Childonella uncinata is the causative agent ofChilodonelloza, a disease that affects the gills and skin of fresh water fish, and may act as afacultative of mosquito larva.
Chilodonella uncinata has a cosmopolitan distribution. It is suspected to act as afacultativeendoparasite of the larvae of theCulex,Aedes, andAnopheles mosquito larva. It lives in fresh water ponds, lakes, creeks, and bayous where it feeds on bacteria and other microbes.
Microscopic examination of cytological samples showed that mosquito larva containing subcutaneous encystedC. uncinata had a 25-100% mortality in the mosquito larva, but no viability examinations were conducted.[6]
Chilodonella uncinata has a broadthigmotactic zone that is two-thirds the length of the body width and has a pronounced anterior beak that is directed to the left.[7] It can be maintained under laboratory conditions in a cereal wheat grass media inoculated withKlebsiella sp. Optimal growth occurs between 25 and 30 °C.C. uncinata is capable ofsporulation and can resist environments with limited resources for a period of time.
Allciliates have twonuclei, but they differ in their structure of the somatic nucleus. Allciliates exceptKaryorelictea have a dividing macronucleus.[8]C. uncinata also has a dividing macronucleus, but it modifies its macronuclear genome from the maternal micronuclear genome by producing macronuclear chromosomes that contain one or twoopen reading frame (ORFs). The average size of these macronuclear chromosomes is 4 kbit/s.[4] The macronuclear chromosomes are also amplified to produce a high variable copy number between the chromosomes. For example, chromosome A may have 500 copies while chromosome B only has 5 copies in the macronucleus. This leaves the macronuclear genome with millions of individual chromosomes, all containingtelomere ends, only one ORF, and little area for transcription factor binding for initiation of transcription.
Internally eliminated sequences (IES) are noncoding regions of thegerm-line genome found inCiliates. They are defined as sections of DNA removed from the diploid micronuclear genome during which a copy of the micronuclear genome is converted to the macronuclear genome even though errors occur in which an IES sequence may not be deleted.[2] There is little conservation of motifs between Ciliate species; however,C. uncinata, like other ciliate species, show a conserved IES sequence motif within a species.[9] It is unknown if IES sequences have a function in the genome, but in the ciliateParamecium, an IES sequence is used to determine the mating type of an individual. When a specific IES sequence is not deleted from the developing somatic nucleus, then it is type O mating type. However, if that IES is deleted from the developing macronucleus, it is type E mating type.Paramecium can only mate with individual of opposite mating type.
UnlikeTetrahymena orParamecium, it has been observed thatC. uncinata has a larger number of IES sequences within a single protein-coding gene than in other ciliates . Also there exists populations ofC. uncinata that contain an IES sequence that other populations do not carry.
Chilodonella uncinata has sexual conjugation forrecombination, and replication of the cell occurs by asexual division[4]
Sex and reproduction are separate in ciliates.[10]C. uncinata is capable of mating with otherC. uncinata cells that have the samemating type. Aftermating type complementary, the germ-line nucleus undergoes meiosis to producezygotic nuclei. Each conjugated cell transfers one zygotic nucleus to the other cell where the zygotic nuclei fuse. The diploid germ-line nucleus undergoes mitosis which creates a duplicated germ-line nucleus. At this point the somatic nucleus is being degraded.
The duplicated germ-line nucleus then develops into the new somatic nucleus. The genomic structure of the somatic nucleus is being created by chromosomal fragmentation with single-gene chromosomes and amplification of these somatic chromosomes. It is unknown what determines the copy number of each chromosome or if the copy number of the somatic chromosomes are heritable between sexual conjugations.
C. uncinata goes through asexual reproduction for cell division and duplication calledamitosis. AsC. uncinata has two nuclei, it goes through two different styles of division of the nuclei. The germ-line nucleus goes throughmitosis during asexual division while the somatic nucleus undergoesamitosis. Amitosis is a stochastic process where unlike in mitosis, there is no spindle formation to segregate chromosomes during nuclear division. Instead, the chromosomes within the somatic nucleus are duplicated, and the nucleus goes through binary division. The precise mechanism is unknown, but it is believed that somatic chromosomes that are located on one side of the dividing somatic nucleus are distributed to one daughter cell, and the somatic chromosomes on the other side of the nucleus are distributed to the other daughter cell.
This amitotic process causes the two daughter cells to potentially have identical germ-line nucleus but a different somatic nucleus in regards to the copy numbers of the chromosomes. As the somatic nucleus is the nucleus that is transcriptionally active, this somatic copy number mutation derived by the amitotic process could have fitness consequences for the individual cell.
Childonella uncinata is easily cultured in the laboratory, has a fast generation time, and has a complex genomic structure that allowsC. uncinata to be amodel organism forgenomic architecture,genomic networks, andgenome evolution research.[11] Specifically,C. uncinata along with other closely relatedCiliates has been used to determine the evolution of duplication of thealpha-tubulin gene. It was found thatC. uncinata contains two paralogs ofalpha-tubulin where the variation between theparalogs is highly concentrated within three small areas of the gene.[12]
Media related toChilodonella uncinata at Wikimedia Commons