| Sterkiella histriomuscorum | |
|---|---|
 | |
Scientific classification  | |
| Domain: | Eukaryota |
| Clade: | Diaphoretickes |
| Clade: | SAR |
| Clade: | Alveolata |
| Phylum: | Ciliophora |
| Class: | Spirotrichea |
| Family: | Oxytrichidae |
| Genus: | Sterkiella |
| Species: | S. histriomuscorum |
| Binomial name | |
| Sterkiella histriomuscorum | |
| Synonyms [1] | |
| |
Sterkiella histriomuscorum, formerly Oxytricha trifallax, is a ciliate species in the genus Sterkiella , known for its highly fragmented genomes which have been used as a model for ciliate genetics.
Like all ciliates, O. trifallax has two different types of nuclei: macronuclei, which are the site of transcription and gene expression, and micronuclei, which are only active during sexual reproduction but are otherwise transcriptionally inactive. Macronuclei are formed by the differentiation of micronuclei, which usually involves some degree of RNA-mediated DNA editing. O. trifallax is the first species sequenced with an unusually high degree of fragmentation in its macronuclear genome. Up to 96% of the micronuclear genome is eliminated during the differentiation into a macronucleus; in comparison, in other ciliates like Paramecium only about 30% is eliminated. The macronuclear genome has a haploid size of about 50 Mbp. [2]
The chromosomes of the macronucleus are also unusually short. The macronuclear genome encodes about 18,500 genes, but these are distributed on 16,000 chromosomes, which are called nanochromosomes due to their length. [2] [3] Because of their unusually short nanochromosomes, most of which contain only a single gene, they have been used as a model organism to study telomeres and to screen for non-coding RNA genes. [4]
The micronuclear genome has also been sequenced, and contains about 3,500 scrambled genes. Scrambled genes are genes whose individual segments are located in different parts of the micronuclear genome, and therefore have to be "unscrambled" during the DNA editing step into a conventional gene in the macronuclear genome. More than 225,000 individual DNA segments have to be unscrambled during the development of a macronuclear genome from its micronuclear precursor. [5]
The mitochondrial genome has also been sequenced, and is the largest known ciliate mitochondrial genome, with a length of about 70 kbp. Like other ciliate mitochondrial genomes, those of O. trifallax are linear molecules and contain a number of split genes. Their mitochondria also possess a separate plasmid, which may have been involved in horizontal gene transfer during the evolution of the mitochondrial genome. [6]
The taxonomy of O. trifallax has been contested. It was reclassified as Sterkiella histriomuscorum on the basis of morphological characteristics, but a molecular phylogeny supports the original classification as a species of Oxytricha. [7]
Tetrahymena, a unicellular eukaryote, is a genus of free-living ciliates. The genus Tetrahymena is the most widely studied member of its phylum. It can produce, store and react with different types of hormones. Tetrahymena cells can recognize both related and hostile cells.
Paramecium is a genus of eukaryotic, unicellular ciliates, commonly studied as a model organism of the ciliate group. Paramecium are widespread in freshwater, brackish, and marine environments and are often abundant in stagnant basins and ponds. Because some species are readily cultivated and easily induced to conjugate and divide, they have been widely used in classrooms and laboratories to study biological processes. The usefulness of Paramecium as a model organism has caused one ciliate researcher to characterize it as the "white rat" of the phylum Ciliophora.
The stichotrichs were a proposed group of ciliates, in the class Spirotrichea. In a classification system proposed by Eugene Small and Denis Lynn in 1985, Stichotrichia formed a subclass containing four orders: Stichotrichida, Urostylida, Sporadotrichida and Plagiotomida. Although the group was made up of species traditionally classified among the "hypotrichs"—ciliates possessing compound ciliary organelles called cirri—it excluded euplotid ciliates such as Euplotes and Diophrys, which were placed in the subclass Hypotrichia. In later classifications proposed by Denis Lynn, Stichotrichia omits the order Plagiotomida.
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, such as metabolism. During conjugation, the macronucleus disintegrates, and a new one is formed by karyogamy of the micronuclei.
A micronucleus is a small nucleus that forms whenever a chromosome or a fragment of a chromosome is not incorporated into one of the daughter nuclei during cell division. It usually is a sign of genotoxic events and chromosomal instability. Micronuclei are commonly seen in cancerous cells and may indicate genomic damage events that can increase the risk of developmental or degenerative diseases.
Nuclear dimorphism is a term referred to the special characteristic of having two different kinds of nuclei in a cell. There are many differences between the types of nuclei. This feature is observed in protozoan ciliates, like Tetrahymena, and some foraminifera. Ciliates contain two nucleus types: a macronucleus that is primarily used to control metabolism, and a micronucleus which performs reproductive functions and generates the macronucleus. The compositions of the nuclear pore complexes help determine the properties of the macronucleus and micronucleus. Nuclear dimorphism is subject to complex epigenetic controls. Nuclear dimorphism is continuously being studied to understand exactly how the mechanism works and how it is beneficial to cells. Learning about nuclear dimorphism is beneficial to understanding old eukaryotic mechanisms that have been preserved within these unicellular organisms but did not evolve into multicellular eukaryotes.
Spirostomum is a genus of ciliated protists in the class Heterotrichea. It is known for being very contractile. Having been first identified by Christian Gottfried Ehrenberg in 1834, further research has identified eight additional true morphospecies. This bacterivore genus mainly lives in the sediment deposits at the bottom of various aquatic habitats, and members possess rquA genes that could be responsible for their ability to survive in these hypoxic and anoxic environments. They are identifiable by their relatively large tubular/flat vermiform bodies. Their life cycle consists of a growth stage, in which they mature, and asexual and sexual reproduction stages. Some species are model organisms for studies on human pathogenic bacteria, while others are sensitive and accurate bioindicators for toxic substances.
39S ribosomal protein L30, mitochondrial is a protein that in humans is encoded by the MRPL30 gene.
Stentor coeruleus is a protist in the family Stentoridae which is characterized by being a very large ciliate that measures 0.5 to 2 millimetres when fully extended.
28S ribosomal protein S11, mitochondrial is a protein that in humans is encoded by the MRPS11 gene.
Karyorelictea is a class of ciliates in the subphylum Postciliodesmatophora. Most species are members of the microbenthos community, that is, microscopic organisms found in the marine interstitial habitat, though one genus, Loxodes, is found in freshwater.
The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to eukaryotic flagella, but are in general shorter and present in much larger numbers, with a different undulating pattern than flagella. Cilia occur in all members of the group and are variously used in swimming, crawling, attachment, feeding, and sensation.
In bioinformatics, the Ciliate MDS/IES database is a biological database of spirotrich genes.
Chilodonella uncinata is a single-celled organism of the ciliate class of alveoles. As a ciliate, C. uncinata has cilia covering its body and a dual nuclear structure, the micronucleus and macronucleus. Unlike some other ciliates, C. uncinata contains millions of minichromosomes 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 facultative of mosquito larva.
Oxytricha is a genus of ciliates in the family Oxytrichidae.
Colpidium colpoda are free-living ciliates commonly found in many freshwater environments including streams, rivers, lakes and ponds across the world. Colpidium colpoda is also frequently found inhabiting wastewater treatment plants. This species is used as an indicator of water quality and waste treatment plant performance.
Laura Faye Landweber is an American evolutionary biologist. As of 2016, she is a professor of biochemistry and molecular biophysics and of biological sciences at Columbia University. Previously, she was a professor of ecology and evolutionary biology at Princeton University. She specializes in RNA-mediated epigenetic inheritance and molecular evolution.
The genome of most cells of eukaryotes remains mainly constant during life. However, there are cases of genome being altered in specific cells or in different life cycle stages during development. For example, not every human cell has the same genetic content as red blood cells which are devoid of nucleus. One of the best known groups in respect of changes in somatic genome are ciliates. The process resulting in a variation of somatic genome that differs from germline genome is called somatic genome processing.
Parduczia is a genus of karyorelict ciliates in the family Geleiidae.