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Unicellular relative of animals


Unicellular relative of animals

In this photo from scanning electron microscope - unicellular amoeboid organism Capsaspora owczarzaki , the only species of the genus Capsaspora . Filopodia — filiform 3–3–333 diverge in all directions from a cell 3–5 ?m in size. pseudopodia , or pseudopods. Capsaspora - representative of treasure Filasterea sisterly for Choanozoa , which includes unicellular collar flagellates, or choanoflagellates , and animals . That is, kapsaspora is one of the closest relatives of animals.

Capsaspores - symbionts tropical river snails living in their hemolymph . They were first discovered in the hemolymph of snail 3-3-33269. Bulinus globosus [/i] , then another 11 other snails, including Biomphalaria glabrata , which has become a source of amoeba for laboratory research. Capsaspores are considered symbionts because of their ability of 3-3-399. kill snail parasites - trematode Schistosome genus (3-3-33269. 3-3-364. Schistosoma mansoni 3-3-33266. 3-33270.) at the stage 3-3-367. maternal sporocysts 3-3-33266. (first 3–3–369. parthenogenetic 3–3–3266. generation in the body of the intermediate host). Amoebas 3-3-3113. stick to the sporocyst, they start filopodia into the pores of the epithelium (3-3-3373. tegument 3-3-33266.) and branch out inside. The affected sporocyst is torn, and its cells are 3-3-375. 3-3-33266 are phagocytosed. amoebas. It is interesting that even dead sporocysts cause active amoeba division and “sticking” with the parasite.


Unicellular relative of animals

Capsaspores were surrounded on all sides by sporocysts of schistosomes an hour after co-cultivation. Individual amoeba are marked by 3–3–3269. arrows [/i] . The length of the scale segment is - 60 microns. Photo from an article by H. H. Stibbs et al., 1979. Schistosome sporocyst-killing amoebae isolated from Biomphalaria glabrata


For the first time, capsaspores 3-3-3109. found in 1968. Then they were called Hartmannella biparia . In 1980 the American scientist Alfred Owczarzak (3f3r3113). carried them to the genus Nuclearia groups 3-3-3119. Nucleariida - freshwater and soil amoeba with filopodia. In 2002 scientists conducted an analysis of 3-3-3121. ribosomal RNA symbiotic amoebas and found that they have much more in common with animals than with Nucleariida. According to genetic and morphological characteristics, there are 3–3–3123 of them. described as a new genus and species Capsaspora owczarzaki , in honor of their researcher.

There are several stages in the life cycle of capsa spores. The main photo shows the philopodial stage. The cell at this stage is attached to the surface - in laboratory conditions it is a solid nutrient medium. At the next stage, the capsa spore is separated from the surface and draws in filopodia, forming 3-3-3129. cyst . Further, cysts freely floating in a liquid medium aggregate, forming a multicellular mass. Scientists consider that the aggregation stage could become a prerequisite for the emergence of multicellularity.

At the stage of aggregation, genes that are active in animals begin to work in cells. For example, Brachyury - one of the oldest genes that regulate the development of multicellular animals, in particular the development of 3-3-3137. chords (see 3-3-3139. Unicellular organisms have a gene capable of controlling the development of the 3-3-33266 chord. Elements, 10252013). Capsaspores also have genes. Myc (family of regulatory genes encoding 3-3-33145. transcription factors 3-3-33266., also some genes regulate the structure of 3-3-3147. chromatin 3-3-33266.) and 3-3-33269. Runx [/i] (encode one of the key regulatory proteins of vertebrates, responsible for the differentiation of blood cells). What processes are responsible for all these genes in unicellular capsaspores is still unknown. In addition, 3–3–3151 are activated at the aggregation stage. integrins (cell receptors interacting with 3-3-3153. extracellular matrix 3-3-33266 and transmitting various intercellular signals) and their associated signaling and cell adhesion proteins (e.g. 3-3-3325. G-protein 3-3-33266.).


Unicellular relative of animals

Two capsa spores at the filopodial stage. Photo © Multicellgenome Lab from flickr.com


Consider the life cycle of capsa spores in laboratory conditions in more detail. At the beginning of cultivation, the amoeboid cell creeps along the substrate, exploring the environment with its filopodia. At this stage, active occurs. DNA replication , which precedes cell division, and within 48 hours, the cells enter the exponential growth phase (that is, actively divide).

Filopodial stage of capsa spore. Dark granules are 3-3-3191. vesicles 3-3-33266. (organelles that store nutrients). In total, nine amoebas

are visible on the video.

Subsequently, the cells begin to separate from the surface and draw in filopodia. After eight days, amoebas are no longer attached and growth is stabilized. Later, cells begin to aggregate. Probably, the aggregation stage allows amoebas not to disperse in the environment or hemolymph of snails - perhaps it’s easier to get to other capsa spore habitats, for example, up to 3-3-3197. pericardium (pericardial sac) snails.

Aggregation of capsaspores. Cells accumulate randomly and form aggregates 3-3-33271.

Amoebas are attached to each other until a compact aggregate is formed. Cells produce an extracellular matrix that forms a rather thick layer - apparently this prevents direct contact between cells.


Unicellular relative of animals

The life cycle of the capsa spore. a - filopodial stage, long filopodia are visible. b - the transition from filopodial to the cyst stage: filopodia begin to be drawn in; c - the cell at the cystic stage is round, without filopodia, slightly smaller in size than the filopodial cell; d - transition from the filopodial stage to the aggregation stage: the cells attach to each other and secrete an extracellular matrix. e - mature unit; f - two adjacent cells separated by an extracellular matrix. Arrows indicate the observed stages of mutual transformation. The length of the scale segments is : a , b , c , e , f - 1 ?m, d - 200 nm. Image from article A. Sebe-Pedros et al., 2013.3-3r3255. Regulated aggregative multicellularity in a close unicellular relative of metazoa


So, capsapsores have genes characteristic of multicellular ones; they undergo regulation of intercellular interactions and the exchange of signals between cells. All this makes capsasspores an interesting object for studying the mechanisms that led to the emergence of multicellularity.

Photo © Multicellgenome Lab from flickr.com .

Anastasia Sheshukova

27 апрель 2020 /
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