Dictyostelium discoideum

In nature, D. discoideum lives in soil and litter (wet leaf litter). Single amoeba D. discoideum feed mainly on bacteria . Distributed D. discoideum in mixed and deciduous forests of the temperate zone ^[2] .

If there is not enough food, amoeba stick together and migrate to where the environment is more favorable. There they decompose into individual cells. Before migration, the amoeba do not eat all available bacteria, but take their supplies with them. In a new place, they scatter them, creating food reserves ^{[3] [4] [5]} .

Spores of D. discoideum are released from mature fruiting bodies and carried by the wind. At a sufficiently high humidity and temperature, myxameba come out of the spores - the unicellular stage of the development of dictostelium. With sufficient moisture and food, they feed and share mitosis . Miksameb attracts folic acid secreted by bacteria.

When food is exhausted, aggregation of mixes begins. At this stage, specific glycoproteins and adenylate cyclase are expressed in myxameb cells ^[6] . Glycoproteins provide intercellular adhesion , adenylate cyclase synthesizes cAMP . cAMP secreted into the medium serves, like in bacteria, as a signal of “cell hunger”. In dictostelium, cAMP is also a chemoattractant for hungry mixes. Several randomly caught together and “stuck together” with the first mixes are the center to which hungry mixes are attracted and crawl from all sides. Connecting with the help of cell adhesion molecules, they form an aggregate of several tens of thousands of cells.

Initially, the flat aggregate makes complex movements, rises above the substrate, and then lies on its side and turns into a migrating “slug” - a mobile pseudoplasmodium 2-4 mm long. Pseudoplasmodium migrates all the time with one end forward, and in its composition cell differentiation begins; part of the cells at the front end form a polysaccharide membrane (pseudoplasmodium migrates through it, and part of it remains on the substrate as a mucous trail) ^[7] . Pseudoplasmodium moves toward light, a higher temperature, and more dry air ^[7] . cAMP and a substance known as the differentiation induction factor (DIF) stimulate further differentiation and the formation of several cell types ^[7] . At the anterior end of pseudoplasmodium, there are cells - the precursors of the stem of the fruiting body, and at the posterior - cells - the precursors of spores. After migration under suitable conditions, pseudoplasmodium cells perform complex movements and form the corresponding parts of the fruiting body ^[7] . “Anterior-like” cells, relatively recently discovered, are distributed in the posterior half of the pseudoplasmodium body; these cells form a stand (the lowest part of the fruiting body) ^[7] .

After the pseudoplasmodium stops due to the movement of cells, the “sombrero stage” is formed, and then the climax phase of the formation of the fruiting body begins.

During this phase, the anterior and posterior pseudo-plasmodium cells change places ^[7] . The front cells of the sombrero form cellulose cell walls and assemble into a hollow tubular stalk, on the outer surface of which the spore precursor cells migrate upward, and the rest of the stem precursor cells downward ^[7] . A fully formed fruiting body 1-2 mm high is formed 8-10 hours after the onset of this phase ^[7] . After maturation, the spores at its peak spores disperse, and the cycle begins again.

In addition to the asexual part of the cycle described above, sexual reproduction can also be present in the life cycle of dictostelium. The transition to sexual reproduction can be triggered by drying of the litter, where mixamebs live. Merging, two mixes of different types of mating form a zygote - a "giant cell". Dictostelium has three types of mating; in 2010, the genetic basis of its “three-cavity” was deciphered ^{[1] [8]} . The zygote begins to swallow the surrounding mixes. After swallowing several hundred mixes, the zygote secretes a thick cellulose membrane, forming the so-called macrocyst. The macrocyst is first divided by meiosis , and then (many times) by mitosis , forming many haploid mixes. Coming out from under the shell of macrocysts, they begin to feed and multiply asexually. Thus, in D. discoideum, the life cycle with zygotic reduction (the only diploid stage is the zygote). In laboratory conditions, sexual reproduction is extremely rare.

The advantages of diktiostelium as a model object are its relatively simple structure, a small number of cell types, as well as a short life cycle and ease of growing under laboratory conditions. At the same time, diktiostelium differs greatly from multicellular animals in the nature of the life cycle and the course of the morphogenesis of fruiting bodies and at the same time is quite similar to them in the identified set of genes and intracellular signaling pathways.

Key research areas

One of the processes intensively studied in dictostelium is the differentiation of cells that occurs during the formation of the fruiting body. In particular, factors affecting the cell’s choice of the differentiation pathway (into the stem or spore cells) were studied depending on the position of pseudoplasmodium in the body, the immediate environment, time from the onset of aggregation, and other factors ^[9] .

Chemotaxis in D. discoideum is studied by the example of the movement of mixomes towards the source of cAMP secretion. In the secretion of cAMP and the speed of movement of mixes, cyclicity with a certain period is observed. Interestingly, the use of cAMP as a chemoattractant has not been described in any other organism ^[7] .

Apoptosis (programmed cell death) during the normal development of the body often serves to ensure the correct relative position of cells and the creation of organs of complex shape. In D. discoideum, about 20% of cells undergo apoptosis during the formation of the fruiting body. These are stalk precursor cells, which secrete the cellulose membrane during stalk formation, and then form large vacuoles and stretch, carrying up the spore precursor cells. Then, the stem cells die by apoptosis ^[10] . In dictostelium, a noticeably smaller number of proteins are involved in the regulation of apoptosis than in vertebrates.

In recent years, other mechanisms of cell death have been intensively studied on dictostelium - through autophagy and necrosis ^[11] .

Also, processes occurring in the cell nucleus are actively studied at dictostelium. Using new techniques for visualizing gene activity, it was shown that transcription in D. discoideum occurs by “flashes”, or “pulses” ^[12] . Later it became clear that such an impulsive nature of transcription is characteristic of all organisms: from bacteria to humans. The set of repair enzymes in dictostelium and in humans is very similar, and this allows us to study the effects of mutations in the genes of the repair system, which in humans are often associated with tumor cell transformation, on such a simple model ^[13] .

The recently developed technology of influencing its genes using CRISPR / Cas9 genomic modifications will significantly advance research on the genetic regulatory mechanisms of dictostelium ^[14]

Laboratory Cultivation

• Superorganism
• Population autowaves