Chilodonella uncinata
Encyclopedia
Childonella uncinata is a single-celled organism of the Ciliate
Ciliate
The ciliates are a group of protozoans characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagella but typically shorter and present in much larger numbers with a different undulating pattern than flagella...

 class of Protists. As a ciliate
Ciliate
The ciliates are a group of protozoans characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagella but typically shorter and present in much larger numbers with a different undulating pattern than flagella...

, C. uncinata has cilia covering its body and a dual nuclear structure, the micronucleus
Micronucleus
A the micronucleus is the smaller nucleus in ciliate protozoans, such as the paramecium. In fission it divides by mitosis, and in conjugation furnishes the pairing of gamete nuclei, by whose reciprocal fusion a zygote nucleus is formed, which gives rise to the macronuclei and micronuclei of the...

 and macronucleus
Macronucleus
A macronucleus is the larger type of nucleus in ciliates. Macronuclei are polyploid and undergo direct division without mitosis. It controls the non-reproductive cell functions, the everyday tasks, such as metabolism...

. Unlike some other ciliates, C. uncinata contains millions of minichromosomes (somatic chromosomes) in its macronucleus while its micronucleus is estimated to contain 3 chromosomes. Childonella uncinata is the causative agent of Chilodonelloza, a disease that affects the gills and skin of fresh water fish, and may act as a facilitative parasite of mosquito larva.

Habitat

Childonella uncinata has a cosmopolitan distribution. It is suspected to act as a facultative
Facultative
Facultative means "optional" or "discretionary" , used mainly in biology in phrases such as:* Facultative anaerobe, an organism that can use oxygen but also has anaerobic methods of energy production...

 endoparasite of the larvae of the Culex
Culex
Culex is a genus of mosquito, and is important in that several species serve as vectors of important diseases, such as West Nile virus, filariasis, Japanese encephalitis, St. Louis encephalitis and avian malaria....

, Aedes
Aedes
Aedes is a genus of mosquito originally found in tropical and subtropical zones, but now found on all continents excluding Antarctica. Some species have been spread by human activity. Aedes albopictus, a most invasive species was recently spread to the New World, including the U.S., by the used...

, and Anopheles
Anopheles
Anopheles is a genus of mosquito. There are approximately 460 recognized species: while over 100 can transmit human malaria, only 30–40 commonly transmit parasites of the genus Plasmodium, which cause malaria in humans in endemic areas...

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 encysted C. uncinata had a 25-100% mortality in the mosquito larva, but no viability examinations were conducted.

Biology and Morphology

Chilodonella uncinata has a broad thigmotatic zone that is two-thirds the length of the body width and has a pronounced anterior beak that is directed to the left. It can be maintained under laboratory conditions in a cereal wheat grass media inoculated with Klebsiella
Klebsiella
Klebsiella is a genus of non-motile, Gram-negative, oxidase-negative, rod-shaped bacteria with a prominent polysaccharide-based capsule. It is named after the German microbiologist Edwin Klebs...

 sp
. Optimal growth occurs between 25 and 30°C. C. uncinata is capable of sporulation and can resist environments with limited resources for a period of time.

Genome Structure

All ciliates have two nuclei, but they differ in their structure of the somatic nucleus. All ciliates except Karyorelictea
Karyorelictea
All ciliate possess multiple dimorphic nuclei which have separated the functions of protein synthesis, preformed by the macronuclei or somatic-nuclei, and heritable DNA replication, performed by the micronuclei or germ-line nuclei...

 have a dividing somatic nucleus. C. uncinata also has a dividing somatic nucleus, but it modifies its somatic genome from the maternal germ-line genome by producing somatic chromosomes that contain one or two open reading frame
Open reading frame
In molecular genetics, an open reading frame is a DNA sequence that does not contain a stop codon in a given reading frame.Normally, inserts which interrupt the reading frame of a subsequent region after the start codon cause frameshift mutation of the sequence and dislocate the sequences for stop...

 (ORFs). The average size of these somatic chromosomes is 4 kbps . The minichromosomes are also amplified to produce a high variable copy number between the minichromosomes. For example, minichromosome A may have 500 copies while minichromosome B only has 5 copies in the somatic chromosome. This leaves the somatic genome with millions of individual chromosomes, all containing telomere
Telomere
A telomere is a region of repetitive DNA sequences at the end of a chromosome, which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes. Its name is derived from the Greek nouns telos "end" and merοs "part"...

 ends, only one ORF, and little area for transcription factor binding for initiation of transcription.

Internally Eliminated Sequences

Internally Eliminated Sequences (IES) are noncoding regions of the germ-line genome found in Ciliates
Ciliate
The ciliates are a group of protozoans characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagella but typically shorter and present in much larger numbers with a different undulating pattern than flagella...

. They are defined as sections of DNA removed from the diploid germ-line genome during which a copy of the germ-line genome is converted to the somatic genome even though errors occur in which an IES sequence may not be deleted. 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 . It is unknown if IES sequences have a function in the genome, but in the Ciliate Paramecium
Paramecium
Paramecium is a group of unicellular ciliate protozoa, which are commonly studied as a representative of the ciliate group, and range from about 0.05 to 0.35 mm in length. Simple cilia cover the body, which allow the cell to move with a synchronous motion at speeds of approximately 12 body...

, 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 somatic nucleus, it is type E mating type. Paramecium can only mate with individual of opposite mating type.

Unlike Tetrahymena
Tetrahymena
Tetrahymena are free-living ciliate protozoa that can also switch from commensalistic to pathogenic modes of survival. They are common in fresh-water. Tetrahymena species used as model organisms in biomedical research are T. thermophila and T. pyriformis.- T...

 or Paramecium
Paramecium
Paramecium is a group of unicellular ciliate protozoa, which are commonly studied as a representative of the ciliate group, and range from about 0.05 to 0.35 mm in length. Simple cilia cover the body, which allow the cell to move with a synchronous motion at speeds of approximately 12 body...

, it has been observed that C. uncinata has a larger number of IES sequences within a single protein-coding gene than in other ciliates . Also there exists populations of C. uncinata that contain an IES sequence that other populations do not carry.

Reproduction and Division

Chilodonella uncinata has sexual conjugation for recombination, and replication of the cell occurs by asexual division

Sexual Conjugation

Sex and reproduction are sepearate in ciliates. C. uncinata is capable of mating with other C. uncinata cells that have the same mating type
Mating type
Mating types occur in eukaryotes that undergo sexual reproduction via isogamy. Since the gametes of different mating types look alike, they are often referred to by numbers, letters, or simply "+" and "-" instead of "male" and "female." Mating can only take place between different mating...

. After mating type
Mating type
Mating types occur in eukaryotes that undergo sexual reproduction via isogamy. Since the gametes of different mating types look alike, they are often referred to by numbers, letters, or simply "+" and "-" instead of "male" and "female." Mating can only take place between different mating...

 complementary, the germ-line nucleus undergoes meiosis to produce zygotic 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.

Asexual Reproduction

All reproduction is asexual. C. uncinata goes through asexual reproduction for cell division and duplication called amitosis
Amitosis
Amitosis is the process by which a cell directly separates, not to be confused with mitosis. Amitosis divides relatively simply, as the nucleus and cytoplasm are directly cut in two. Unlike regular mitosis, no spindles or the formation and appearance of chromosomes are involved in amitosis...

. As C. uncinata has two nuclei, it goes through two different styles of division of the nuclei. The germ-line nucleus goes through mitosis
Mitosis
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...

 during asexual division while the somatic nucleus undergoes amitosis
Amitosis
Amitosis is the process by which a cell directly separates, not to be confused with mitosis. Amitosis divides relatively simply, as the nucleus and cytoplasm are directly cut in two. Unlike regular mitosis, no spindles or the formation and appearance of chromosomes are involved in amitosis...

. 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.

Use in genomic research

Childonella uncinata is easily cultured in the laboratory, has a fast generation time, and has a complex genomic structure that allows C. uncinata to be a model organism
Model organism
A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. Model organisms are in vivo models and are widely used to...

 for genomic architecture, genomic networks, and genome evolution research. Specifically, C. uncinata along with other closely related Ciliates has been used to determine the evolution of duplication of the alpha-tubulin gene. It was found that C. uncinata contains two paralogs of alpha-tubulin where the variation between the paralogs is highly concentrated within three small areas of the gene.
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK