The leading edge of motile cells is propelled by polymerization of actin filaments according to a dendritic nucleation/array treadmilling mechanism. However, little attention has been given to the ...origin and maintenance of the dendritic array. Here we develop and test a population-kinetics model that explains the organization of actin filaments in terms of the reproduction of dendritic units. The life cycle of an actin filament consists of dendritic nucleation on another filament (birth), elongation by addition of actin subunits and, finally, termination of filament growth by capping protein (death). The regularity of branch angle between daughter and mother filaments endows filaments with heredity of their orientation. Fluctuations of branch angle that become fixed in the actin network create errors of orientation (mutations) that may be inherited. In our model, birth and death rates depend on filament orientation, which then becomes a selectable trait. Differential reproduction and elimination of filaments, or natural selection, leads to the evolution of a filament pattern with a characteristic distribution of filament orientations. We develop a procedure based on the Radon transform for quantitatively analyzing actin networks in situ and show that the experimental results are in agreement with the distribution of filament orientations predicted by our model. We conclude that the propulsive actin network can be understood as a self-organizing supramolecular ensemble shaped by the evolution of dendritic lineages through natural selection of their orientation.
Cell motility requires lamellipodial protrusion, a process driven by actin polymerization. Ena/VASP proteins accumulate in protruding lamellipodia and promote the rapid actin-driven motility of the ...pathogen
Listeria. In contrast, Ena/VASP negatively regulate cell translocation. To resolve this paradox, we analyzed the function of Ena/VASP during lamellipodial protrusion. Ena/VASP-deficient lamellipodia protruded slower but more persistently, consistent with their increased cell translocation rates. Actin networks in Ena/VASP-deficient lamellipodia contained shorter, more highly branched filaments compared to controls. Lamellipodia with excess Ena/VASP contained longer, less branched filaments. In vitro, Ena/VASP promoted actin filament elongation by interacting with barbed ends, shielding them from capping protein. We conclude that Ena/VASP regulates cell motility by controlling the geometry of actin filament networks within lamellipodia.
Positioning of the mitotic spindle through the interaction of astral microtubules with the cell boundary often determines whether the cell division will be symmetric or asymmetric. This process plays ...a crucial role in development. In this paper, a numerical model is presented that deals with the force exerted on the spindle by astral microtubules that are bent by virtue of their confinement within the cell boundary. It is found that depending on parameters, the symmetric position of the spindle can be stable or unstable. Asymmetric stable equilibria also exist, and two or more stable positions can exist simultaneously. The theory poses new types of questions for experimental research. Regarding the cases of symmetric spindle positioning, it is necessary to ask whether the microtubule parameters are controlled by the cell so that the bending mechanics favors symmetry. If they are not, then it is necessary to ask what forces external to the microtubule cytoskeleton counteract the bending effects sufficiently to actively establish symmetry. Conversely, regarding the cases with asymmetry, it is now necessary to investigate whether the cell controls the microtubule parameters so that the bending favors asymmetry apart from any forces that are external to the microtubule cytoskeleton.
Transport of organelles along microtubules is essential for the cell metabolism and morphogenesis. The presented analysis derives the probability that an organelle of a given size comes in contact ...with the microtubule aster. The question is asked how this measure of functionality of the microtubule aster is controlled by the centrosome. A quantitative model is developed to address this question. It is shown that for the given set of cellular parameters, such as size and total tubulin content, a centrosome nucleation capacity exists that maximizes the probability of the organelle capture. The developed general model is then applied to the capture of the female pronucleus by microtubules assembled on the sperm centrosome, following physiologically polyspermic fertilization. This application highlights an unintuitive reflection of nonlinearity of the nucleated polymerization of the cellular pool of tubulin. The prediction that the sperm centrosome should lower its nucleation capacity in the face of the competition from the other sperm is a stark illustration of the new optimality principle. Overall, the model calls attention to the capabilities of the centrosomal pathway of regulation of the transport-related functionality of the microtubule cytoskeleton. It establishes a quantitative and conceptual framework that can guide experiment design and interpretation.
Prostate cancer (PC) diagnostics and treatment often present a challenging task due to cancer subtype heterogeneity and differential disease progression in patient subgroups. Hence, the critical ...issue is finding a reliable and sensitive diagnostic and prognostic PC marker, especially for cases of biopsies with low percentages of cancer cells. Isoform A of myosin 1C was shown to be expressed in PC cells and responsible for their invasive properties, however, its feasibility for diagnostic purposes remains to be elucidated.
To verify the role of myosin 1C isoform A mRNA expression as a putative prostate cancer marker we performed RT qPCR normalized by three reference genes (
) on PC3, RWPE-1, LNCaP and 22Rv1 cell lines. Myosin 1C isoform A detection specificity was confirmed by immunofluorescence staining, cancer and non-cancer prostate cell lines were immunophenotyped by flow cytometry.
Median normalized mRNA expression level of myosin 1C isoform A in PC cells (PC3 and 22Rv1) is two orders of magnitude higher compared to RWPE-1 cells, which functionally correspond to benign prostate cells. Myosin 1C isoform A expression allows PC cell detection even at a dilution ratio of 1:1000 cancer to non-cancer cells. At the protein level, the mean fluorescence intensity of myosin 1C isoform A staining in PC3 nuclei was only twice as high as in RWPE-1, while the immunophenotypes of both cell lines were similar (CD44+/CD90-/CD133-/CD57-/CD24+-).
We report a distinct difference in myosin 1C isoform A mRNA levels in malignant (PC3) and benign (RWPE-1) prostate cell lines and suggest a combination of three reference genes for accurate data normalization. For the first time we provide an immunophenotype comparison of RWPE-1 and PC3 cells and demonstrate that RT qPCR analysis of
using appropriate reference genes is sufficient for PC detection even in low-abundance cancer specimens.
The article deals with the method of determining the optimal composition of the components of the combined fuel taking into account the heat-dynamic tension in the operation of the diesel engine on a ...mixture of diesel fuel and natural gas, i.e. the gas-diesel cycle. The calculation was based on the method developed by A. V. Grinevetsky and M. N. Mezingom, taking into account the specific conditions of the diesel engine on a mixture of natural gas and diesel fuel. The peculiarity of the mathematical model is that the optimal composition of the fuel components is initially unknown and is indicated as an array. The search for the optimal ratio of fuel components will take into account the heat and Dynamo tension. The resulting model can be used in the study of the diesel engine on other alternative fuels. Thus, it is possible to significantly improve the quality of the fuel combustion process, thereby increasing the engine power and ensuring the environmental safety of exhaust gases.
T-killer cells of the immune system eliminate virus-infected and tumorous cells through direct cell-cell interactions. Reorientation of the killing apparatus inside the T cell to the T-cell interface ...with the target cell ensures specificity of the immune response. The killing apparatus can also oscillate next to the cell-cell interface. When two target cells are engaged by the T cell simultaneously, the killing apparatus can oscillate between the two interface areas. This oscillation is one of the most striking examples of cell movements that give the microscopist an unmechanistic impression of the cell's fidgety indecision. We have constructed a three-dimensional, numerical biomechanical model of the molecular-motor-driven microtubule cytoskeleton that positions the killing apparatus. The model demonstrates that the cortical pulling mechanism is indeed capable of orienting the killing apparatus into the functional position under a range of conditions. The model also predicts experimentally testable limitations of this commonly hypothesized mechanism of T-cell polarization. After the reorientation, the numerical solution exhibits complex, multidirectional, multiperiodic, and sustained oscillations in the absence of any external guidance or stochasticity. These computational results demonstrate that the strikingly animate wandering of aim in T-killer cells has a purely mechanical and deterministic explanation.
We have studied the effect of sintering temperature on the structural and phase transformations of alloys produced by the spark plasma sintering of Ti + 23.5 at % Al + 21 at % Nb powder mixtures at ...temperatures in the range 1100–1550°C. The sintered alloys have been characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy (elemental X-ray mapping). The alloys sintered at temperatures of 1100 and 1200°C have been shown to have a nonuniform microstructure. According to electron microscopy results, the alloys consist of grains of the α
2
and Nb
2
Al phases and small precipitates of the O-phase (intermetallic compound Ti
2
AlNb). In addition, there are particles of unreacted niobium and titanium. The alloys sintered at a temperature of 1300°C have a uniform lamellar structure.
T-killer cells eliminate infected and cancerous cells with precision by positioning their centrosome near the interface (immunological synapse) with the target cell. The mechanism of centrosome ...positioning has remained controversial, in particular the role of microtubule dynamics in it. We re-examined the issue in the experimental model of Jurkat cells presented with a T cell receptor-binding artificial substrate, which permits controlled stimulation and reproducible measurements. Neither 1-microM taxol nor 100-nM nocodazole inhibited the centrosome positioning at the "synapse" with the biomimetic substrate. At the same time, in micromolar taxol but not in nanomolar nocodazole the centrosome adopted a distinct peripheral rather than the normally central position within the synapse. This effect was reproduced in a computational energy-minimization model that assumed no microtubule dynamics, but only a taxol-induced increase in the length of the microtubules. Together, the experimental and computational results indicate that microtubule dynamics are not essential for the centrosome positioning, but that the fit of the microtubule array in the deformed body of the conjugated T cell is a major factor. The possibility of modulating the T-cell centrosome position with well-studied drugs and of predicting their effects in silico appears attractive for designing anti-cancer and antiviral therapies.
Constitutive exocytosis delivers newly synthesized proteins, lipids, and other molecules from the Golgi apparatus to the cell surface. This process is mediated by vesicles, which bud off the ...trans-Golgi network, move along cytoskeletal filaments, and fuse with the plasma membrane. Here, we show that the small GTPase Rab6 marks exocytotic vesicles and, together with the microtubule plus-end-directed motor kinesin-1, stimulates their processive microtubule-based transport to the cell periphery. Furthermore, Rab6 directs targeting of secretory vesicles to plasma-membrane sites enriched in the cortical protein ELKS, a known Rab6 binding partner. Our data demonstrate that although Rab6 is not essential for secretion, it controls the organization of exocytosis within the cellular space.
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