Where is the centrosomes located

The centrioles are surrounded by an amorphous matrix of proteins, commonly referred to as the pericentriolar material PCM , which contains proteins involved in nucleation and anchoring of microtubules, as well as important cell cycle regulators and other signaling molecules. The centrosomes, as well as the basal body of cilia, is closely surrounded by cytoplasmic granules, known as centriolar satellites Tollenaere MA et al.

Centriolar satellites travel along microtubules by association with motor proteins and are known to contain a number of proteins that are also found in centrosomes and cilia. Centriolar satellites can be observed in most cell types, but their composition, size, number and location varies.

Centriolar satellites disassemble upon entry into mitosis, bur reappear upon completion of cytokinesis. A selection of proteins suitable as markers for the centrosome and the centriolar satellites can be found in Table 1. A list of highly expressed proteins that localize to centrosomes and centriolar satellites are summarized in Table 2.

Table 1. Selection of proteins suitable as markers for the centrosome and centriolar satellites. Table 2. Highly expressed centrosome and centriolar satellite marker proteins, in different cell lines. See the morphology of centrosomes in human induced stem cells in the Allen Cell Explorer. The major function of the centrosome is organization of microtubules in the cell, thereby controlling cellular shape, polarity, proliferation, mobility and cell division.

During S-phase, the centrosome is replicated in a semi-conservative manner, resulting in formation of one daughter centriole next to each of the parental centrioles. As the cell approaches mitosis, the two centrosomes, each containing a parental centriole and a maturing procentriole, move to opposite ends of the cell.

At the same time, the amount of surrounding PCM proteins increase, enabling nucleation of more microtubules. When the nuclear membrane breaks down, microtubules originating from each of the centrosomes can interact with kinetochores on the replicated sister chromatids, forming the characteristic mitotic spindle. The intricate spindle apparatus mediates separation of sister chromatids to opposite ends of the cell, and upon cytokinesis each of the daughter cells is provided with one set of chromosomes and one centrosome.

The parental centriole, i. Centriolar satellites have long been considered as vehicles for protein trafficking to and from the centrosome and cilia, thus playing a role in dynamic regulation of protein composition in these organelles Tollenaere MA et al.

Indeed, several proteins that localize to centriolar satellites have been implicated in centrosome replication, maturation and separation. However, in recent studies, centriolar satellites have also emerged as regulators of multiple other cellular processes, such as protein degradation and autophagy, some of which are independent of centrosomes and cilia.

Similarly, centrosomes and cilia are not fully dependent on centriolar satellites. As key regulators of chromosome segregation and cell cycle progression, abnormalities in number, size and morphology of the centrosome, and mutations in genes encoding protein that localize to centrosomes, is commonly observed in cells undergoing tumorigenesis, but also in some other diseases Badano JL et al. Gene Ontology GO -based analysis of genes encoding proteins that localize to centrosomes or centriolar satellites shows enrichment of terms describing functions that are well in-line with existing literature.

The most highly enriched terms for the GO domain Biological Process are related to mitosis and cytokinesis, cell cycle progression, endocytosis, organization of the microtubule cytoskeleton, and organization of organelles Figure 3a. Enrichment analysis of the GO domain Molecular Function reveal enrichment of terms describing binding to microtubules and motor proteins, as well as motor activity Figure 3b. Figure 3a. Gene Ontology-based enrichment analysis for the centrosome proteome showing the significantly enriched terms for the GO domain Biological Process.

A single centriole is also to be found at the basal end of cilia and flagella. Centrioles present something of an enigma Centrioles are present in 1 animal cells and 2 the basal region of cilia and flagella in animals and lower plants e.

When animal cells undergo mitosis they are considered by some to benefit from the presence of centrioles which appear to control spindle fibre formation and which later has an effect on chromosome separation. Research however has shown that mitosis can take place in animal cells after centrioles have been destroyed. Sometimes this seems to be at the expense of abnormalities in spindle development and subsequent problems with chromosome separation.

Recent research also suggests that embryos of Drosophila arrest very early if centriole replication cannot take place. In higher plants mitosis takes place perfectly satisfactorily with microtubules forming spindle fibres but without the help of centrioles.

The function of centrioles therefore remains something of a mystery. Structure A centriole is composed of short lengths of microtubules arranged in the form of an open-ended cylinder about nm long and nm in diameter. The microtubules forming the wall of the cylinder are grouped into nine sets of bundles of three microtubules each.

In cilia and flagella where centrioles are at the base of the structure, and are called basal bodies, the wall and cavity architecture is slightly different. In addition to cylinder walls composed of nine sets of bundles of three microtubules, there are walls of nine sets of two bundles. It is interesting that in poorly differentiated epithelial cells, for example, in the intestinal crypt, the centrosome is located more precisely in the center of the cells, and only during differentiation, for example, in the intestinal villi, moves to the apical part [ 12 , 13 , 14 , 15 , 16 ].

The centrosome located in the apical part of the cells often organizes a basal-apical microtubule bundle [ 26 ], which provides transcytosis, i. In differentiated cells, the centrosome sometimes loses the function of organizing microtubules, passing it to the non-centrosomal structures [ 12 , 13 , 14 , 15 , 16 , 26 ].

Moreover, it remains itself in the apical part of the cell, although few direct observations of this have been published. Sometimes, centrioles in differentiated cells degrade, and most of the cells in the intestinal villi do not have centrioles at all [ 14 , 15 , 16 ]. In many tissues, the centrosome forms the primary cilium protruding above the surface of the epithelial or endothelial layer or into the nephron duct [ 18 ].

In intestine cells cilia form only at embryos [ 16 ]. Upon the induction of cilia formation in cultured cells, during serum starvation, their centrosome also shifts to the part of the cell remote from the substrate [ 27 ], corresponding to the apical side of the epithelium Figure 1 I,J.

In actively proliferating cultured cells, the centrosome is usually located in the part of the cell close to the substrate. Special mention should be made of the planar cell polarity PCP , which refers to the uniform polarization of cells within the plane of a cell sheet [ 28 , 29 , 30 , 31 ]. With this phenomenon, when it comes to projection onto a plane orthogonal to the basal-apical, centrosomes are often shifted to one edge of the cells.

A pronounced PCP is observed, for example, in Drosophila wing cells during the formation of actin-supported protrusions—hairs, which, as well as centrosomes, are shifted to the distal edge of the cells. Therefore, the PCP phenomenon has been studied mainly in Drosophila , although in recent years a lot of work has been done on other objects.

The formation of rows of stereocilia and uniformly oriented motile cilia also belong to the PCP phenomenon reviewed in [ 28 , 29 , 30 , 31 ]. We will not focus on this issue further. PCPs are more often found in the epithelium, although in many cases, it is not clear whether PCP exists in any epithelium, or whether the centrosome is shifted in a planar plane simply by chance.

It is noteworthy that in the vascular endothelium, centrosomes are usually shifted to the edge of the cells facing the heart [ 20 ]. The shift of the centrosome to the leading edge of the fibroblasts is apparently also a special case of PCP due to the polarization of their actomyosin system, although the fibroblasts do not form an integral layer.

During the epithelial-mesenchymal transition EMT , which accompanies carcinogenesis and a series of events during embryogenesis, the centrosome in the epithelial cell moves from the apical to the basal part, which becomes anterior during further migration through the extracellular matrix ECM , which is characteristic of mesenchymal cells [ 23 ] Figure 1 F—H.

As mentioned previously, the location of the centrosome in fibroblasts and fibroblast-like cells has been studied mainly in culture; there are very few works that observed it in fibroblasts in situ [ 6 ]. Another particular case of natural displacement of the centrosome is the formation of an immune synapse Figure 1 D,E.

It was noted that in polymorphonuclear leukocytes attached to a ferritin substrate, the centrosome is located mainly apically, and on the ferritin substrate with anti-ferritin antibodies, it moves to the basal part [ 32 ]. Centrosome displacement into the caudal region of the lymphocyte by which it attaches to the antigen-presenting cell or the target cell [ 33 , 34 , 35 , 36 , 37 ] is accompanied by the destruction of the connection of the centrosome to the nucleus and the formation of an immune synapse.

The centrosome, coupled with the Golgi apparatus, always adjoins the immune synapse, organizing there an amplified bundle of microtubules.

Similarly, in fibroblast-like cells that are polarized on the substrate, the centrosome is also located close to the Golgi, and both these organelles are often—although not always—shifted to the leading edge [ 5 ]. However, the centrosomal displacement to the immune synapse is usually compared to the shift of the centrosome to the apical edge of the cell during cilia formation [ 38 ] and not with the movement of the fibroblast.

Centrosome localization in mature neurons in situ is poorly understood. In differentiating neurons, the centrosome is often, but not always, located at the site of axon exit. During migration of the neuron, it appears at the leading edge, ahead of the nucleus. According to some reports, when a neuron moves, the centrosome first moves forward to the leading neurite; then, a nucleus is pulled behind it, surrounded by a network of microtubules.

However, other studies have shown the independent movement of centrosomes and nuclei during the migration of neurons, when the centrosome is either in front of or behind the nucleus. Herewith, the centrosome moves uniformly, keeping up with the center of the cell, and the nucleus can make saltatory movements, either ahead of the centrosome or lagging behind it [ 39 ]. Similar oscillatory movements are performed by the nucleus and centrosome when glioma cells move along thin lines coated with fibronectin [ 40 ].

Interphase centrosomes were mainly studied in in situ objects, though there are also many observations of the location of mitotic spindles in developing multilayer and single layer epithelium, where it is important for whether the cell divides vertically or horizontally relative to the epithelial layer, as well as along or across the axis of the tubular epithelial structures [ 17 , 41 ].

In the collecting duct in a developing kidney, cells divide along it [ 17 ]. The location of the spindles across the epithelial layer is important for the formation of the stratified epithelium.

The spindles find the right position, navigating by the shape of the cells and, of course, by the properties of the cell cortex [ 42 , 43 ].

In particular, the location of the interphase centrosome and the presence of the primary cilia are important [ 17 ]. Thus, three types of centrosome positioning can be highlighted: 1 the centrosome is located close to the centroid of the projection of the cell onto the plane, which is especially characteristic of non-motile and non-polarized cultured cells, taking into account the thickness of the actin cortex; 2 a shift to one of the cell edges during cell polarization PCP, EMT, etc.

All three types of centrosome positioning and movements may be due to different molecular mechanisms, although, of course, they are interconnected. It has been suggested, however, that both centering and centrosomal displacement can be determined by the same mechanism, depending on the absence or presence of at least small external cues [ 44 ]. As mentioned previously, the function of the central location of the centrosome in the cells is not clear.

It is difficult to determine this function, if only because there are no experimental approaches for centrosome decentering that do not involve serious effects on the cytoskeleton. Therefore, we must confine ourselves to speculative discussions about the creation of a certain cell geometry, in particular, about the centrosome-nucleus axis in moving cells. It is possible that both the reason and purpose of the central location of the centrosome is to create a relatively symmetric radial microtubules network, which allows for the organizing of directional transport to the centrosome of the components necessary for its functioning, including cilia growth [ 2 ], i.

The central location of mitotic spindles, in which the poles are formed by centrosomes, is more understandable. The spindle shift leads to a shift of the cleavage furrow and the formation of daughter cells of unequal size.

Numerous examples of asymmetric mitoses are well-known when the mitotic spindle is shifted from the center of cells due to some physiological mechanisms and, as a result of mitosis, unequal cells are formed: where the spindle pole was closer to the plasmalemma, the daughter cell turns out to be smaller. This phenomenon can be observed, in particular, during the division of Drosophila neuroblasts or mouse cerebellar cells [ 46 ].

Limits to the sizes of mitotic spindles and the regulation of their location are discussed in detail in several works [ 42 , 47 , 48 ]. The regulation of cell sizes is discussed in the review [ 49 ]; we will not dwell further on these topics.

The consequences of a shift of the centrosome from the center of the cell in the interphase are rather the opposite of the consequences of its shift in mitosis. If, in mitosis, a smaller pole of the fission spindle moves toward the plasmalemma, then in the interphase, the increased number of microtubules usually reaches the edge of the cell to which the centrosome moves, which can be clearly seen in the example of an immune synapse or even moving fibroblasts.

The centrosome is often accompanied by the Golgi, at whose membranes additional microtubules are formed, which also go to the edge of the cell [ 50 ]. These microtubules appear to be used for enhanced transport to the outside of the vesicles containing, for example, metalloproteases that remodel ECM when the fibroblast moves [ 51 ], or enzymes that destroy the target cell of T-killer [ 37 ]. However, it has been shown that microtubules that are not associated with a centrosome are needed to polarize the endothelial cells of a growing vessel, while the centrosome, on the other hand, can inhibit cell polarization [ 52 ], especially in the presence of an excess of centrioles [ 53 ].

Another reason for the shift of the centrosome from the center to the edge of the cell is the formation of a primary or motile cilium or flagellum. It is believed that the same mechanisms are involved in the formation of the immune synapse and primary cilia, and they are discussed below. Finally, the centrosome shifts to the edge of the cell during PCP, for example, when strictly oriented hairs form on the wing cells of the Drosophila.

The direct mechanisms of this shift remain unknown, although it has been established that, upstream, they depend on the dynamics of the actin cytoskeleton and on Wnt signaling. To shift the centrosome to the edge of the cell, it is necessary to initially shift it to the apical part, which always depends on actin [ 54 ].

In summary, the central arrangement of the centrosome arises due to the intrinsic properties of the cytoskeleton; we can assume that it is necessary for the selfish functions of the centrosome. The shift of the centrosome to the edge of the cell is regulated through the signal transduction pathways [ 5 ] and serves to fulfill the functions of the cells or the organ in which the cell is located. Let us first consider why the centrosome is often located in the centroid in the projection of cells onto a plane.

All researchers agree that the microtubule aster surrounding the centrosome plays the main role in centering. In particular, aster holds the centrosomes in the cells when enucleation is made under cytochalasin treatment [ 55 ]. Recent discoveries have shown that the centrosome initiates the polymerization of not only microtubules but also actin filaments [ 56 ]. However, most models of centrosome centering are based on the participation of cytoplasmic dynein interacting with microtubules.

The role of dynein in centrosome centering has been shown in many experimental works [ 57 , 58 , 59 , 60 ], in which dynein activity was inhibited by low molecular weight inhibitors or the introduction of inhibitory proteins into the cell for example, the CC1 fragment of the pGlued protein and a sharp centrosome displacement from the center was observed.

It has been confirmed that the cell cortex in cultured cells contains many dynein molecules, coupled with its cofactor dynactin [ 61 ] and, in addition, many dynein molecules are located on intracellular membrane structures Figure 2 A,B. If Dictyostelium has two centrosomes in the binuclear cell, they form two independent asters, each occupying its own territory in the cytoplasm.

Laser ablation of one of the asters leads to the rapid centering of the second aster, which is well-explained by the action of pulling forces from the side of the dynein [ 62 ]. Based on the general properties of the cytoskeleton, we can assume the effect of various forces on the aster: pushing forces from microtubule polymerization, pulling and pushing forces from microtubule motors, pushing and pulling forces from actomyosin interacting with microtubules, and pushing and pulling forces from actomyosin itself.

Geometry and mechanism of the centrosome centering. A —multiple dynein molecules pulling the microtubule from the cell periphery. B —pulling forces applied by dynein molecules anchored at the surface of cytoplasmic organelles along the microtubule. C —pushing forces generated by growing microtubule plus-end.

The forces applied to microtubules by the actin cortical flow are not shown on this figure D —links between the centrosome and the nucleus. Central panel: note that the pulling forces are applied in actin inner zone only, and curved microtubules outside it do not contribute to centering [ 9 ]. It was previously shown, with our participation, that the centrosome is kept at the center by a pulling force generated by dynein acting along microtubules and actin flow produced by myosin contraction [ 58 ].

These results were obtained from experiments with cells in which local microtubule destruction LMD was performed by the local application of nocodazole; moreover, the inhibition of the activity of dynein, myosin actin flow inhibition , or microtubule dynamics were implemented. The results [ 58 , 63 ] are summarized in Table 1.

Position of centrosome in culture cells with local microtubule disruption LMD data from [ 58 ]. In the article of Zhu et al. The total equation can be expressed as:. Obviously, F push depends on the f push , developed by a single microtubule, on the number of dynamic microtubules and the depth of dynamic instability; F act depends on f act the effect of actin flow per unit length of microtubules and the length of microtubules to the second degree; F dyn depends on f dyn the strength of one dynein molecule and the length of microtubules.

The corresponding equations can be found in the Supplemental Material of [ 63 ]. To simplify, if the centrosome is shifted from the center of the cell, for example, to the right, then it has longer microtubules on the left, and then, both the outward pulling to the left F dyn and inward pushing to the right F act are larger on the left; shorter microtubules on the right develop increased F push , pushing to the left.

The solution of the derived equations with parameters satisfying the experimental data was carried out. In the best way they corresponded per one microtubule to f dyn proportional to 3 f push , and f act proportional to 8 f push. In a computer simulation using the example of a round-shaped cell, the centrosome behavior described in Table 1 was fully reproduced. The centering mechanism was predicted to be robust: all that is needed for the centrosome centering is for the total dynein force to be greater than a modest threshold of 1 motor pulling per microtubule.

The centrosome centering according to the described mechanism was reproduced on round, elliptical, square, and fan-shaped cell models. An interesting observation was made, reproduced both in vivo and in silico: when inhibiting dynein, the centrosome shifts to the long edge of the elliptical cell. This is a consequence of the strict dependence of the F act value on the distance to the cell edge.

Unfortunately, subsequent works paid little attention to the role of the actomyosin system in the behavior of centrosomes, although, as we see, this role is significant. It turned out to be convenient to study further issues by modeling both in silico and in vitro the microfabricated cells where isolated centrosomes and microtubule proteins were placed. In the work of Wu et al.

In silico modeling demonstrated that, in a small cell, the centrosome can occupy the center due only to the dynamics of microtubules pushing forces , though in larger cells and a simulated viscous medium such as the cytoplasm, the pulling by dynein must apply [ 60 ].

In an in vitro system, centrosomes and tubulin were placed in microfabricated cells or inside liposomes, where an aster of microtubules formed, and the walls of the cells or liposomes were coated with dynein from the inside [ 64 , 65 ]. It was shown that dynein activates the catastrophes of microtubules growing to the dynein-covered barrier covered by it, and it significantly improves the centering of aster in a small volume.

The asymmetry in the distribution of dynein leads to the decentering of such an aster. A particular problem is the centrosome centering in very large cells—for example, the movement of spermal aster associated with the male pronucleus and formed by the centrosome of the spermatozoon toward the female pronucleus located in the center of the oocyte of sea urchin, Xenopus , or C.

The microtubules of spermal aster may not reach the oocyte cortex with their ends, but the aster, along with the pronucleus, moves to the center of the oocyte at a fairly high speed [ 67 , 68 , 69 , 70 ]. This movement depends on microtubules and dynein, but does not depend on actomyosin [ 69 , 70 ]. It is believed that aster movement may be due to the dynein-dependent movement of small vesicles along microtubules to the center of the aster; vesicles move inward, and reactive forces pull microtubules outward [ 67 , 68 , 71 , 72 ].

Mutations and knockdown of genes encoding several proteins involved precisely in the minus-end transport light chain of dynein DYRB-1, rilp-1 , rab-7 , and rab-5 in C. It should be noted that the spermal aster moves in the cytoplasm of the zygote along with the male pronucleus, i.

Under this condition, the pushing forces from the microtubules are insufficient, and calculations show that the centration process cannot go without the action of dynein, though a dozen molecules of dynein are enough to develop the necessary forces [ 73 ]. Howard and Garzon-Coral [ 74 ], however, believe that pushing forces play the primary role in spindle centering, if microtubule buckling occurs at the plasmalemma. In the process of conjunction and the subsequent centering of pronuclei in the C.

Simple phenomena, such as the accumulation of yolk at the vegetative pole of an egg, can lead to a change in the action vectors of various forces to the spindle of division and displace the spindle—and, after it, the division plane of the blastomeres [ 75 ]. In Letort et al. In all cases, the simulated microtubules were longer than the radius of the cell. It turned out that the centrosome-organized aster moves to the center of the round-shaped cell only by dynein pulling forces, with both a cortically located dynein and a dynein distributed over the cytoplasm.

Using cell models of an ellipsoidal, rectangular, and triangular shape, it was found that with a uniform distribution of dynein in the cytoplasm, in all cases it is possible to achieve close to the central position of the centrosome.

However, the greatest distance from the center of the aster to the cell centroid was obtained in triangles, especially in a triangle with a wide base. With the cortical arrangement of dynein in triangles, the simulated center of the aster was always shifted from the centroid. It also turned out that centering due to pushing forces was possible only in the absence of microtubule pivoting and gliding, i.

In general, the aster centering was facilitated by a decrease in the stiffness of microtubules, an increase in their dynamics, and a diminution in the number. The introduction of asymmetric pulling forces produced by dynein molecules located on one of the sides of the round-shaped cell led to a sharp decentration of the aster [ 64 , 65 ]. Actin can play a special role in the location of centrosomes in a cell.

Centrosome separation before mitosis depends not only from the intactness of the MT network, but also on the intactness of the actin filaments [ 77 ]. Actin develops forces opposed to the kinesin Eg5, which promotes centrosome separation [ 79 ]. Jimenez et al. To describe the architecture of the actin cytoskeleton, the authors introduced new concepts of Actin Inner Zone AIZ , i. In a symmetric cell, AIC is the same as a centroid. It turned out that the position of the centrosome corresponds to the position of the AIC in both symmetric and asymmetric cells.

If you treat a cell with a ROCK kinase inhibitor Y , which suppresses the assembly of F-actin and retrograde actin flow, and removes actin bundles from the edges bordering AIZ, then actin is redistributed throughout the cell homogeneously, while AIC shifts and begins to coincide with the centroid—and the centrosome moves there too.

Because the centrosome centering is due to the forces applied to the astral microtubules, the authors studied their architecture depending on the localization of the actin and found that microtubules are straight and radial in the AIZ which indicates their tension and the force applied to them but entangled outside this zone.

Thus, even if MTs are knotty outside the AIZ, their radiality in the central zone will ensure successful centering. Experiments with cytoplasts of different sizes, but with approximately the same AIZ, showed that the accuracy of centrosome positioning depends on the size of the AIZ, and not on the whole size of the cell.

Microtubules extending from the centrosome can interact with actin through either specific crosslinkers or non-specific steric interactions [ 80 ]. In particular, dense-growing actin networks can apply pushing forces to microtubules [ 81 , 82 ]. One cannot help but mention another unobvious contribution of actin to centrosome positioning. In the work of Inoue et al. They physically block the formation of centrosomal microtubules at the earliest stages of their polymerization.

The centrosomal actin affects the magnitude of the microtubule pushing forces generated by newly formed microtubules. Thus, not only does peripheral actin restrict AIZ involved in centrosome centering, but also centrosomal actin, which limits the nucleation of microtubules on the centrosome and, thus, affects the magnitude of the forces applied to it. As already mentioned, the nucleus also seeks to occupy a central position in the cell, and to some extent competes with the centrosome for this position.

The centrosome is associated with the nucleus reviewed in [ 10 ] and is usually located at a distance of about 0. When the nucleus has a multilobulated morphology, as in neutrophils, the centrosome is located inside the nucleus courtyard [ 1 , 32 , 84 ]. The mutual arrangement of the nucleus and centrosome was investigated using above-described model of round-shaped and triangular-shaped single cells grown on a micropatterned substrate [ 3 ].

The association of the centrosome with the nucleus weakens, and the distance between these organelles increases with the disruption of microtubules by the action of nocodazole. When actin filaments were destroyed by the action of latrunculin B, the nucleus was displaced from the centroid and the distance from it to the centrosome increased as well.

In round-shaped cells with depleted lamin A of the nuclear membrane, the distance between the centrosome and the nucleus increased significantly, probably due to the inability of the cytoskeletal structures to attach to the nucleus. Notably, in fibroblasts gliding along the substrate, the retrograde movement of the nucleus depends mainly on the dorsal actin filaments attached to the nucleus via the nesprin and SUN protein complexes of the nuclear membrane [ 85 ].

It is supposed that both the nucleus and the centrosome independently try to occupy a central position in the cell, with the position of the centrosome being determined mainly by the microtubule network, and the position of the nucleus by the actin network, but the nucleus and centrosome are connected by a separate bundle of microtubules [ 3 ]. However, we believe that they are also linked by actin and that the location in the cell of both the nucleus and the centrosome is determined by the coordinated action of cytoskeletal structures, which was demonstrated in [ 40 ].

Mainly, the movement of a nucleus through a cell depends on both actomyosin and microtubules-dynein, depending on the direction of movement [ 86 ]. The positioning of the centrosome in the cell also depends on some of its proteins, in particular, TBCCD1, from the family of tubulin chaperones.

The distance from the centrosome to the nucleus also increases when hypoxia and inflammation act on the cells, which leads to their release of ATP and the activation of the A2 purinergic receptor. Supporting data were also obtained with cells growing on a micropatterned substrate [ 89 ]. RPE cells were seeded to crossbow-shaped adhesive patterns, which forced them to take on the shape of a fan, with the sides being unattached to the substrate.

This led to an asymmetric distribution of actin, actin-binding proteins, and microtubule plus ends. The nucleus in these cells was somewhat shifted from the centroid to the narrow part of the cell, and the axis of the nucleus-centrosome formed in a manner directed from the narrow to the wide part of the fan. In all cases, the cells externally had a square shape, but were attached to the substrate, and their non-attached edges were located differently Figure 3.

It turned out that the nucleus-centrosome axis in all cases was directed toward more adhesions, with the centrosome always located in the centroid of the cell and with the nucleus shifted toward free edges.

The authors believe that proteins that bind actin and microtubules, such as APC, concentrate on the adhesive edges of the cells and capture the plus ends of the microtubules, stopping their growth and exposing them to pulling forces.

Along the non-adhesive edges of the cell the microtubules continue to grow without binding to the cortex until they reach the next adhesive zone [ 89 ]. Actin polarization affects the location of the nucleus.

The cells were seeded in adhesive patterns of different forms top row. The nucleus-centrosome axis in all cases was directed toward more adhesions shown with red , with the centrosome always located in the centroid of the cell and with the nucleus shifted toward free edges shown with blue.

Based on data described in [ 89 ]. The natural polarization of cells depends on the ability of protein complexes to separate at different cell edges, with PAR proteins playing the most important role, while the rest of the proteins migrate through the cell, integrating into one or the other complex [ 90 , 91 ]. Dynein is needed for polarization and directional movement of fibroblasts [ 92 ].

The shift of dynein to the front of the cell is regulated by FAK kinase [ 93 ] and with the participation of cdc42, polarity protein Dlg1, which interacts with dynein via the scaffolding protein GKAP [ 94 ]. In addition, some authors have paid attention to local changes in the dynamics of microtubules, which can occur, for example, at the leading edge of fibroblasts moving along the substrate [ 95 , 96 , 97 ].

Such changes can influence pushing forces elaborated by microtubules. In particular, the paxillin focal contact protein inhibits HDAC6 deacetylase and increases microtubule acetylation in the front of the cell, which leads to the shifting of the centrosome and Golgi apparatus there [ 98 ]. The actomyosin system also plays a role in the movement of the centrosome.

With the participation of DISC1 disrupted in schizophrenia 1 , a phosphorylated form of myosin II accumulates in the centrosome. This is necessary for proper centrosome orientation and radial migration of developing mouse neurons [ 99 ].

Such a myosin can interact with centrosomal actin. In the epithelial sheets, the centrosome is held in the apical part of the cell by microtubules associated with intercellular adhesions and, possibly, by the apically located actin cortex.

Obviously, for the apical displacement of the centrosome, it is first necessary to establish the basal-apical polarization of the cell. For the formation of the lumen of the ducts at least in the culture of renal cells , certain ECM properties and tight cell packing are necessary [ ]. During lumen formation, GTPase cdc42 accumulates on the apical membrane. Interestingly, the activity of cdc42 in the plasmalemma is necessary for the proper organization of the centrosome, including centrioles and pericentriolar material [ ].

Microtubules extending from the centrosome are fixed at adhesions, especially astral microtubules in mitosis [ 43 ], but microtubules extending from apically displaced interphase centrosome can be fixed as well.

In fact, the detailed mechanism of apical displacement of the centrosome has not been studied; it was shown that actin-binding proteins ERM and merlin are involved in displacement [ 80 ]. Interestingly, ERM and merlin similarly provide centrosome clustering in the case of the presence of multiple centrosomes in the cell, which confirms that these proteins participate in the centrosome movement through the cell [ 80 ], although the mechanism of this participation is obscure.

Actin-dependent apical centrosomal displacement is necessary for their subsequent proximal-distal polarization during PCP development [ 54 ].