Functions of nonmuscle myosin II in assembly of the cellular contractile system.

The contractile system of nonmuscle cells consists of interconnected actomyosin networks and bundles anchored to focal adhesions. The initiation of the contractile system assembly is poorly understood structurally and mechanistically, whereas system's maturation heavily depends on nonmuscle myosin II (NMII). Using platinum replica electron microscopy in combination with fluorescence microscopy, we characterized the structural mechanisms of the contractile system assembly and roles of NMII at early stages of this process.

Rearrangements of the actin cytoskeleton and E-cadherin-based adherens junctions caused by neoplasic transformation change cell-cell interactions.

E-cadherin-mediated cell-cell adhesion, which is essential for the maintenance of the architecture and integrity of epithelial tissues, is often lost during carcinoma progression. To better understand the nature of alterations of cell-cell interactions at the early stages of neoplastic evolution of epithelial cells, we examined the line of nontransformed IAR-2 epithelial cells and their descendants, lines of IAR-6-1 epithelial cells transformed with dimethylnitrosamine and IAR1170 cells transformed with N-RasG12D. IAR-6-1 and IAR1170 cells retained E-cadherin, displayed discoid or polygonal morphology, and formed monolayers similar to IAR-2 monolayer.

Comparative dynamics of retrograde actin flow and focal adhesions: formation of nascent adhesions triggers transition from fast to slow flow.

Dynamic actin network at the leading edge of the cell is linked to the extracellular matrix through focal adhesions (FAs), and at the same time it undergoes retrograde flow with different dynamics in two distinct zones: the lamellipodium (peripheral zone of fast flow), and the lamellum (zone of slow flow located between the lamellipodium and the cell body). Cell migration involves expansion of both the lamellipodium and the lamellum, as well as formation of new FAs, but it is largely unknown how the position of the boundary between the two flow zones is defined, and how FAs and actin flow mutually influence each other. We investigated dynamic relationship between focal adhesions and the boundary between the two flow zones in spreading cells.

Controlling cell length.

Control of cell dimensions is an important but poorly understood aspect of morphogenesis. In this review, our primary focus is on control of cell length in different types of cells and cytoskeletal regulation of this parameter. Cell length is not a constant characteristic of certain cell type but of cells of fibroblastic morphology.

Regulation of polarity in cells devoid of actin bundle system after treatment with inhibitors of myosin II activity.

Interplay of two cytoskeletal systems--microfilaments and microtubules is essential for directional cell movement. To better understand the role of those cytoskeletal systems in polarization of cells, rat fibroblasts were incubated with drugs inhibiting activity of myosin II: blebbistatin and Y-27632. Both drugs led to disappearance of actin-myosin bundles and mature focal cell-matrix adhesions but did not affect polarization and directional motility.

Transformation by RAS oncogene decreases the width of substrate-spread fibroblasts but not their length.

We compared morphometric parameters of the contours of cells in four pairs of non-transformed mouse and rat lines and of the same lines transformed by oncogenes of the RAS family. As expected, the mean areas of all RAS-transformed lines were much smaller than those of their non-transformed counterparts. At the same time the average length of cell projection did not regularly decrease after transformation.

ROS up-regulation mediates Ras-induced changes of cell morphology and motility.

Expression of activated Ras causes an increase in intracellular content of reactive oxygen species (ROS). To determine the role of ROS up-regulation in mediation of Ras-induced morphological transformation and increased cell motility, we studied the effects of hydrogen peroxide and antioxidant NAC on morphology of REF52 rat fibroblasts and their ability to migrate into the wound in vitro. Treatment with low dosages of hydrogen peroxide leading to 1.

Cytoskeletal mechanisms responsible for invasive migration of neoplastic cells.

Cytoskeletal reorganizations, especially alterations of contractile tension generated by the actin-myosin cortex, are of central importance in the development of the phenotype of morphologically transformed neoplastic cells with invasive behavior. These reorganizations can be regarded as genetically determined aberrations of the physiological reactions of normal cells which are responsible for their ability to undergo exploratory migrations, including epithelio-mesenchymal transformations, invasion of matrix by epithelial tubules etc. It is suggested that these physiological and neoplastic transformations are based on Rho-dependent alterations in contractility.

Length control is determined by the pattern of cytoskeleton.

In our previous experiments with linear strips of adhesive substrate, we found that elongated cultured fibroblasts preserve their length regardless of cell width and the number of cytoplasmic processes. This constancy of length was called 'length control'. In contrast to fibroblasts, single cultured epitheliocytes have nearly discoid shape on the plane substrata and have no length-controlling mechanism: their length on the narrow strips of adhesive substrate increased significantly in comparison with the diameter on the plane substrate.

Thread-grain transition of mitochondrial reticulum as a step of mitoptosis and apoptosis.

Association of mitochondrial population to a mitochondrial reticulum is typical of many types of the healthy cells. This allows the cell to organize a united intracellular power-transmitting system. However, such an association can create some difficulties for the cell when a part of the reticulum is damaged or when mitochondria should migrate from one cell region to another.

Mechanism of filopodia initiation by reorganization of a dendritic network.

Afilopodium protrudes by elongation of bundled actin filaments in its core. However, the mechanism of filopodia initiation remains unknown. Using live-cell imaging with GFP-tagged proteins and correlative electron microscopy, we performed a kinetic-structural analysis of filopodial initiation in B16F1 melanoma cells.