Entamoeba
Entamoeba | |
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Entamoeba histolytica trophozoite | |
Scientific classification ![]() | |
Domain: | Eukaryota |
Phylum: | Amoebozoa |
Family: | Entamoebidae |
Genus: | Entamoeba Casagrandi & Barbagallo, 1897 |
Type species | |
Entamoeba coli (Grassé 1879) Casagrandi & Barbagallo 1895
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Species | |
E. bangladeshi | |
Synonyms | |
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Entamoeba is a
Species
Several species are found in humans and animals. Entamoeba histolytica is the pathogen responsible for invasive '
Structure
![](http://upload.wikimedia.org/wikipedia/commons/thumb/7/71/Parasite130116-1-olm_Entamoeba_gingivalis_microscopy.tif/lossy-page1-220px-Parasite130116-1-olm_Entamoeba_gingivalis_microscopy.tif.jpg)
Entamoeba cells are small, with a single
Classification
Entamoeba belongs to the
Culture
Fission
Studying Entamoeba invadens, David Biron of the Weizmann Institute of Science and coworkers found that about one third of the cells are unable to separate unaided and recruit a neighboring amoeba (dubbed the "midwife") to complete the fission.[6] He writes:
- When an amoeba divides, the two daughter cells stay attached by a tubular tether which remains intact unless mechanically severed. If called upon, the neighbouring amoeba midwife travels up to 200 μm towards the dividing amoeba, usually advancing in a straight trajectory with an average velocity of about 0.5 μm/s. The midwife then proceeds to rupture the connection, after which all three amoebae move on.
They also reported a similar behavior in Dictyostelium.[7]
Since E. histolytica does not form cysts in the absence of bacteria, E. invadens has become used as a model for encystation studies as it will form cysts under axenic growth conditions, which simplifies analysis.[8] After inducing encystation in E. invadens, DNA replication increases initially and then slows down. On completion of encystation, predominantly tetra-nucleate cysts are formed along with some uni-, bi- and tri-nucleate cysts.[9]
Differentiation and cell biology
Uninucleated trophozoites convert into cysts in a process called encystation. The number of nuclei in the cyst varies from 1 to 8 among species and is one of the characteristics used to tell species apart. Of the species already mentioned, Entamoeba coli forms cysts with 8 nuclei while the others form tetra-nucleated cysts. Since E. histolytica does not form cysts in vitro in the absence of bacteria, it is not possible to study the differentiation process in detail in that species. Instead the differentiation process is studied using E. invadens, a reptilian parasite that causes a very similar disease to E. histolytica and which can be induced to encyst in vitro. Until recently there was no genetic transfection vector available for this organism and detailed study at the cellular level was not possible. However, recently a transfection vector was developed and the transfection conditions for E. invadens were optimised which should enhance the research possibilities at the molecular level of the differentiation process.[10][11]
Meiosis
In sexually reproducing eukaryotes, homologous recombination (HR) ordinarily occurs during meiosis. The meiosis-specific recombinase, Dmc1, is required for efficient meiotic HR, and Dmc1 is expressed in E. histolytica.[12] The purified Dmc1 from E. histolytica forms presynaptic filaments and catalyzes ATP-dependent homologous DNA pairing and DNA strand exchange over at least several thousand base pairs.[12] The DNA pairing and strand exchange reactions are enhanced by the eukaryotic meiosis-specific recombination accessory factor (heterodimer) Hop2-Mnd1.[12] These processes are central to meiotic recombination, suggesting that E. histolytica undergoes meiosis.[12]
Studies of E. invadens found that, during the conversion from the tetraploid uninucleate trophozoite to the tetranucleate cyst, homologous recombination is enhanced.[13] Expression of genes with functions related to the major steps of meiotic recombination also increased during encystations.[13] These findings in E. invadens, combined with evidence from studies of E. histolytica indicate the presence of meiosis in the Entamoeba.
References
- S2CID 6297817.
- ^ *Casagrandi, O.; Barbagallo, P. (1895). "Ricerche biologiche e cliniche sull' Amoeba coli (Lösch). (Nota preliminare)". Bollettino delle Sedute della Accademia Gioenia di Scienze Naturali in Catania. 39: 4.
- S2CID 46363085.
- PMID 10361303.
- PMID 21940643.
- PMID 11260701.
- PMID 18688845.
- S2CID 218475533.
- PMID 20727884.
- PMID 22321531.
- PMID 22426570.
- ^ PMID 26422142.
- ^ PMID 24098652.
External links
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