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{{distinguish|text=the [[ocellus]] (pl. ''ocelli''), a simple light-sensitive structure found in invertebrates}} |
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Um nicht alles zu wiederholen, weshalb die Kat. mMg sinnvoll ist, verweise ich auf [[Kategorie Diskussion:NKWD#Kategorie:NKWD-Befehl|DS von Kat. NKWD]]. Das hätte allerdings einige Änderungen bei der Benennung von paar Artikeln zur Folge. Wie gesagt, plädiere für die Unterscheidung von Befehl und Operation. --[[Benutzer:Mfgsu|Mfgsu]] ([[Benutzer Diskussion:Mfgsu|Diskussion]]) 02:58, 5. Apr. 2019 (CEST) |
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[[File:Bmc evol bio hoppenrath proterythropsis ocelloid fig1a.png|thumb|right|A [[light microscopy|light micrograph]] of an ocelloid-containing dinoflagellate. The [[cell nucleus|nucleus]] is marked '''n''', the ocelloid is indicated with a double arrowhead, and a posterior cell extension is indicated with an arrow; scale bar = 10 µm.<ref name=hoppenrath />|alt=An image of a single cell featuring a large nucleus and an ocelloid, which is composed of a roundish "lens" and a darkly pigmented disc-shaped retinal body.]] |
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An '''ocelloid''' is a subcellular structure found in the [[family (biology)|family]] ''[[Warnowiaceae]]'' (warnowiids), which are a members of a group of [[unicellular organism]]s known as [[dinoflagellate]]s. The ocelloid is analogous in structure and function to the [[eye]]s of [[multicellular]] organisms, which focus, process and detect light. The ocelloid is much more complex than the [[eyespot apparatus|eyespot]], a light-sensitive structure also found in unicellular organisms, and is in fact one of the most complex known subcellular structures.<ref name="gavelis">{{cite journal |title=Eye-like ocelloids are built from different endosymbiotically acquired components |authors=Gregory S. Gavelis, Shiho Hayakawa, Richard A. White III, Takashi Gojobori, Curtis A. Suttle, Patrick J. Keeling, Brian S. Leander |journal=Nature |year=2015 |doi=10.1038/nature14593 |pmid=26131935 |volume=523 |issue=7559 |pages=204–7}}</ref> It has been described as a striking example of [[convergent evolution]].<ref>{{cite journal|last1=Richards|first1=Thomas A.|last2=Gomes|first2=Suely L.|title=Protistology: How to build a microbial eye|journal=Nature|date=1 July 2015|volume=523|issue=7559|pages=166–167|doi=10.1038/nature14630|pmid=26131934}}</ref> |
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==History== |
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The ocelloid was originally described in 1884.<ref name=gomez>{{cite journal|last1=Gómez|first1=Fernando|last2=López-García|first2=Purificación|last3=Moreira|first3=David|title=Molecular Phylogeny of the Ocelloid-Bearing Dinoflagellates and (Warnowiaceae, Dinophyceae)|journal=Journal of Eukaryotic Microbiology|date=September 2009|volume=56|issue=5|pages=440–445|doi=10.1111/j.1550-7408.2009.00420.x|pmid=19737196}}</ref> Early descriptions were met with skepticism and hypothesized to represent the eye of a multicellular organism coincidentally engulfed by a single-celled organism.<ref name=gavelis /> The possibility that it had an evolutionary relationship to [[plastid]]s had been considered at least since the 1970s, although until the 2010s direct evidence was scarce.<ref name=hayakawa /> |
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==Structure== |
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[[File:Bmc evol bio hoppenrath proterythropsis ocelloid fig1e.png|thumb|left|A micrograph of a single ocelloid; scale bar = 5 µm.<ref name=hoppenrath />|alt=A close-up image of an ocelloid.]] |
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[[File:Plos one hayakawa erythropsidinium ocelloid EM fig1b.png|thumb|right|A [[negative staining]] [[transmission electron micrograph]] of an ocelloid (white box), indicating the hyalosome (H) and retinal body (R), as well as a portion of the piston (Ps). Scale bar = 10 µm.<ref name=hayakawa />|alt=Grayscale electron micrograph of an ocelloid in its cellular context. Due to the microscopy technique used, the normally translucent hyalosome appears almost as darkly stained as the retinal body.]] |
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Ocelloids contain subcomponents analogous to eye structures including the [[lens (anatomy)|lens]], [[cornea]], [[iris (anatomy)|iris]], and [[retina]].<ref name=gavelis /> It can be divided into two substructures, the translucent, roundish ''hyalosome'' and the heavily [[pigment]]ed ''melanosome'', also known as the retinal body or pigment cup.<ref name=hayakawa>{{cite journal|last1=Hayakawa|first1=Shiho|last2=Takaku|first2=Yasuharu|last3=Hwang|first3=Jung Shan|last4=Horiguchi|first4=Takeo|last5=Suga|first5=Hiroshi|last6=Gehring|first6=Walter|last7=Ikeo|first7=Kazuho|last8=Gojobori|first8=Takashi|last9=Gribaldo|first9=Simonetta|title=Function and Evolutionary Origin of Unicellular Camera-Type Eye Structure|journal=PLoS ONE|date=3 March 2015|volume=10|issue=3|pages=e0118415|doi=10.1371/journal.pone.0118415|pmid=25734540|pmc=4348419}}</ref> The hyalosome serves as the refractive [[lens (anatomy)|lens]] of the ocelloid; it is surrounded by a layer of [[mitochondria]] serving as the cornea and has constrictive rings analogous to the [[iris (anatomy)|iris]]. The retinal body has internal structure reminiscent of [[thylakoid]] membranes in [[chloroplast]]s and contains proteins related to [[bacteriorhodopsin]], a light-sensitive protein found in some [[archaea]].<ref name=gavelis /><ref name=hayakawa /> |
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Using [[single cell genome sequencing|single-cell]] [[genomics]] and [[electron microscopy]] techniques, the ocelloid has been shown to consist of multiple [[cell membrane|membrane-bound]] [[organelle]]s with distinct [[endosymbiotic]] origins deriving from multiple lineages of [[peridinin]]-containing [[plastid]]s.<ref name="gavelis" /> This discovery received widespread attention in [[popular science]] media after it was reported in 2015.<ref>{{Cite web|title = Single-Celled Creature Has Eye Made of Domesticated Microbes|url = http://phenomena.nationalgeographic.com/2015/07/02/single-celled-creature-has-eye-made-of-domesticated-microbes/|accessdate = 2015-07-30|first = Ed|last = Yong|date = 2 July 2015|website = Phenomena: Not Exactly Rocket Science|publisher = National Geographic}}</ref><ref>{{Cite web|title = Single-celled predator evolves tiny, human-like 'eye'|url = http://phys.org/news/2015-07-single-celled-predator-evolves-tiny-human-like.html|accessdate = 2015-07-30|date = 1 July 2015|website = Phys.org}}</ref><ref>{{Cite web|title = The Most Unbelievable Eye on Earth Belongs to a Creature With No Brain|url = https://www.pbs.org/wgbh/nova/next/nature/the-most-unbelievable-eye-on-earth-belongs-to-a-creature-with-no-brain/|accessdate = 2015-07-30|date = 16 July 2015|website = Nova Next|publisher = PBS|last = Eck|first = Allison}}</ref> |
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==Function== |
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[[File:Plos one hayakawa erythropsidinium ocelloid EM figS1.png|thumb|right|Comparison between the structures of the ocelloid (1) and the [[vertebrate]] eye (2). Components are indicated as the hyalosome (H), retinal body/retina (R), and [[crystallin]] lens (C).<ref name=hayakawa />|alt=Grayscale diagrams of the structures of the ocelloid and vertebrate eye, showing analogous positional relationships between the hyalosome/lens and retinal body/retina.]] |
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Due to the strong structural resemblance between the ocelloid and [[metazoan]] eyes, it has long been speculated that the ocelloid functions as a photoreceptor; however, this is difficult to determine experimentally because warnowiids cannot be [[cell culture|cultured]] in the laboratory, and isolates from natural habitats degrade quickly. It has been shown that the morphology of the ocelloid changes in response to environmental illumination, that the ocelloid structure can be disrupted by exposure to extremely bright light, and that it contains proteins with [[sequence homology|sequence similarity]] to known light-sensitive proteins.<ref name=hayakawa /> It has been speculated that the ocelloid aids in detecting [[prey]], possibly other dinoflagellates.<ref name=gavelis /> |
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==Evolution== |
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Ocelloids are considered a [[synapomorphic]] character for the warnowiids - that is, they are present in all warnowiids and presumed present in the common ancestor, but are not present in the closest extant relatives, the [[polykrikoid]] dinoflagellates. These two groups share other unusually complex subcellular structures such as [[nematocyst (dinoflagellate)|nematocyst]]s and [[piston (subcellular structure)|piston]]s.<ref name=hoppenrath>{{cite journal|last1=Hoppenrath|first1=M|last2=Bachvaroff|first2=TR|last3=Handy|first3=SM|last4=Delwiche|first4=CF|last5=Leander|first5=BS|title=Molecular phylogeny of ocelloid-bearing dinoflagellates (Warnowiaceae) as inferred from SSU and LSU rDNA sequences.|journal=BMC Evolutionary Biology|date=25 May 2009|volume=9|pages=116|pmid=19467154|doi=10.1186/1471-2148-9-116|pmc=2694157}}</ref><ref name=gomez /> |
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The molecular evidence is compelling that ocelloids are composed of multiple [[endosymbiont]]s: [[mitochondria]] and at least one type of [[plastid]]. Ocelloids are likely to be [[homology (biology)|homologous]] to much less complex plastid-containing [[eyespot apparatus|eyespots]] found in other, distantly related dinoflagellates.<ref name=gavelis /> |
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* [[Evolution of the eye]] |
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* [[Eyespot apparatus]] |
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==References== |
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{{reflist|30em}} |
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==External links== |
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* {{youtube|v6voldJVGC4|''Erythropsidinium'' ocelloid dinoflagellates}} |
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[[Category:Organelles]] |
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[[Category:Sensory receptors]] |
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Aktuelle Version vom 5. April 2019, 02:58 Uhr
Hinweis
[Quelltext bearbeiten]Um nicht alles zu wiederholen, weshalb die Kat. mMg sinnvoll ist, verweise ich auf DS von Kat. NKWD. Das hätte allerdings einige Änderungen bei der Benennung von paar Artikeln zur Folge. Wie gesagt, plädiere für die Unterscheidung von Befehl und Operation. --Mfgsu (Diskussion)