Biomedical subjects

Vladimir Rodionov

Publications and source records attributed to Vladimir Rodionov.

10 recordsLinked to original sources

PubMed2005

Centering of a radial microtubule array by translocation along microtubules spontaneously nucleated in the cytoplasm.

Positioning of a radial array of microtubules (MTs) in the cell centre is crucial for cytoplasmic organization, but the mechanisms of such centering are difficult to study in intact cells that have pre-formed radial arrays. Here, we use cytoplasmic fragments of melanophores, and cytoplasts of BS-C-1 cells to study MT centering mechanisms. Using live imaging and computer modelling, we show that the MT aster finds a central location in the cytoplasm by moving along spontaneously nucleated non-astral MTs towards a point at which MT nucleation events occur equally on all sides. We hypothesize that similar mechanisms, in the presence of the centrosome, contribute to this centering mechanism and ensure the robustness of cytoplasmic organization.

Animals↗

PubMed2005

Multiscale trend analysis of microtubule transport in melanophores.

Microtubule-based transport is critical for trafficking of organelles, organization of endomembranes, and mitosis. The driving force for microtubule-based transport is provided by microtubule motors, which move organelles specifically to the plus or minus ends of the microtubules. Motor proteins of opposite polarities are bound to the surface of the same cargo organelle. Transport of organelles along microtubules is discontinuous and involves transitions between movements to plus or minus ends or pauses. Parameters of the movement, such as velocity and length of runs, provide important information about the activity of microtubule motors, but measurement of these parameters is difficult and requires a sophisticated decomposition of the organelle movement trajectories into directional runs and pauses. The existing algorithms are based on establishing threshold values for the length and duration of runs and thus do not allow to distinguish between slow runs and pauses, making the analysis of the organelle transport incomplete. Here we describe a novel algorithm based on multiscale trend analysis for the decomposition of organelle trajectories into plus- or minus-end runs, and pauses. This algorithm is self-adapted to the characteristic durations and velocities of runs, and allows reliable separation of pauses from runs. We apply the proposed algorithm to compare regulation of microtubule transport in fish and Xenopus melanophores and show that the general mechanisms of regulation are similar in the two pigment cell types.

Animals↗

PubMed2005

Multiphoton-excited microfabrication in live cells via Rose Bengal cross-linking of cytoplasmic proteins.

We demonstrate the use of multiphoton-excited photochemistry to cross-link three-dimensional matrices directly from cytoplasmic proteins in a live cell (starfish oocyte). Fluorescence recovery after photobleaching measurements were used to determine diffusion coefficients inside intracellular cross-linked structures, and it was found that the diffusion was approximately 3 to 4 orders of magnitude slower than in free solution and 2-3 orders of magnitude slower than in cytoplasm and that the value can be tuned by controlling the laser exposure. Complex structures can be fabricated to construct channels and compartments that could be used to isolate cellular processes, and the method should thus be applicable to a broad range of problems in cell biology.

Animals↗

PubMed2005

Intracellular organelle transport: few motors, many signals.

Bidirectional microtubule-dependent organelle transport in melanophores is regulated by cAMP through organelle-bound protein kinase A (PKA); however, the mechanisms responsible for this regulation are unknown. A recent study by Gelfand and colleagues demonstrates that, in addition to PKA, transport is regulated by the organelle-bound mitogen-activated protein kinase (MAPK) signaling components ERK and MEK, whose activity is required for bidirectional transport along microtubules. This pathway apparently acts downstream of PKA, suggesting that bidirectional organelle transport is regulated by a hierarchical cascade of signaling pathways.

Animals↗

PubMed2004

Intracellular actin-based transport: how far you go depends on how often you switch.

Intracellular molecular motor-driven transport is essential for such diverse processes as mitosis, neuronal function, and mitochondrial transport. Whereas there have been in vitro studies of how motors function at the single-molecule level, and in vivo studies of the structure of filamentary networks, studies of how the motors effectively use the networks for transportation have been lacking. We investigate how the combined system of myosin-V motors plus actin filaments is used to transport pigment granules in Xenopus melanophores. Experimentally, we characterize both the actin filament network, and how this transport is altered in response to external signals. We then develop a theoretical formalism to explain these changes. We show that cells regulate transport by controlling how often granules switch from one filament to another, rather than by altering individual motor activity at the single-molecule level, or by relying on structural changes in the network.

Actins↗

PubMed2004

Cytoplasmic dynein nucleates microtubules to organize them into radial arrays in vivo.

Numerous evidence demonstrates that dynein is crucial for organization of microtubules (MTs) into radial arrays, but its exact function in this process is unclear. Here, we studied the role of cytoplasmic dynein in MT radial array formation in the absence of the centrosome. We found that dynein is a potent MT nucleator in vitro and that stimulation of dynein activity in cytoplasmic fragments of melanophores induces nucleation-dependent formation of MT radial array in the absence of the centrosome. This new property of dynein, in combination with its known role as an MT motor that is essential for MT array organization in the absence and presence of the centrosome, makes it a unique molecule whose activity is necessary and sufficient for the formation and maintenance of MT radial arrays in cells.

Animals↗

PubMed2004

Imagination of body rotation can induce eye movements.

OBJECTIVE: Several studies have shown that spatiotemporal aspects of motion are stored and can be retrieved with the use of vestibular and somatosensory cues. The purpose of this study was to examine whether intentional imagination of body rotation can induce oculomotor activity similar to the typical vestibulo-ocular reflex (VOR). MATERIAL AND METHODS: Normal subjects without known vestibular and/or oculometric abnormalities were instructed to imagine a sensation of accelerating body rotation in the horizontal plane (rightward or leftward) while sitting in darkness with closed eyes, using only vestibular and somatosensory cues and not imaginary visual cues. Eye movements were recorded during the imagery session and also during a full, routine electronystagmography (ENG) test. All subjects selected for this study showed normal results in the ENG test, and none of them had gaze-evoked or end-point nystagmus. RESULTS: In response to imaginary rotations, horizontal eye movements were found in 91/121 recordings (75%) in 10 subjects. A typical pattern of nystagmus (0.3-3 Hz, 3-30 degrees /s maximal speed of slow component) was recorded in 53% of mental rightward rotations and 49% of leftward rotations. The fast component was always in the direction of the imaginary rotation (similar to a normal VOR). Other types of eye movement comprised either contralateral eye drift ( approximately 17% of trials) or macro square waves. In 25% of the recordings no definite eye movements could be detected during the mental maneuvers. CONCLUSION: These mentally induced eye movements seem to be due to a cortical process which can affect the normal input to the brainstem nuclei. A possible mechanism is discussed. This phenomenon may serve as an objective measurement of mental activity, may be used for testing the cognitive resources of patients and can probably be used for enhancing the rehabilitation process after acute vestibular insult.

Adolescent↗

PubMed2003

Switching between microtubule- and actin-based transport systems in melanophores is controlled by cAMP levels.

BACKGROUND: Intracellular transport involves the movement of organelles along microtubules (MTs) or actin filaments (AFs) by means of opposite-polarity MT motors or actin-dependent motors of the myosin family. The correct delivery of organelles to their different destinations involves a precise coordination of the two transport systems. Such coordination could occur through regulation of the densities of the two cytoskeletal systems or through regulation of the activities of the cytoskeletal motors by signaling mechanisms. RESULTS: To investigate the mechanisms of switching between MT and AF-dependent transport, we examine the influence of the densities of the MT and AF network on pigment transport in fish melanophores. We also change signaling by using activators and inhibitors of Protein Kinase A (PKA). We find that the key parameters characterizing pigment granule transport along MTs do not depend on MT density and are not significantly altered by complete disruption of AFs. In contrast, the kinetics of changes in these parameters correlate with the kinetics of changes in the intracellular levels of cAMP and are affected by the inhibitors of PKA, suggesting the regulation of MT- and AF-dependent motors by cAMP-induced signaling. Furthermore, perturbation of cAMP levels prevents the transfer of pigment granules from MTs onto AFs. CONCLUSIONS: We conclude that the switching of pigment granules between the two major cytoskeletal systems is independent of the densities of MT or AF but is tightly controlled by signaling events.

Actin Cytoskeleton↗

PubMed2003

Centrosome positioning in interphase cells.

The position of the centrosome is actively maintained at the cell center, but the mechanisms of the centering force remain largely unknown. It is known that centrosome positioning requires a radial array of cytoplasmic microtubules (MTs) that can exert pushing or pulling forces involving MT dynamics and the activity of cortical MT motors. It has also been suggested that actomyosin can play a direct or indirect role in this process. To examine the centering mechanisms, we introduced an imbalance of forces acting on the centrosome by local application of an inhibitor of MT assembly (nocodazole), and studied the resulting centrosome displacement. Using this approach in combination with microinjection of function-blocking probes, we found that a MT-dependent dynein pulling force plays a key role in the positioning of the centrosome at the cell center, and that other forces applied to the centrosomal MTs, including actomyosin contractility, can contribute to this process.

Actins↗

PubMed2003

Analysis of visual evoked potentials and background electroencephalographic activity in young and elderly subjects.

OBJECTIVE: New techniques developed in this laboratory to overcome the loss of information involved in conventional evoked potential averaging are applied here to visual evoked potential (VEP) in young and elderly normal subjects. METHODS: The techniques are based on statistical descriptions of the times and amplitudes of the electroencephalographic deflections recorded before (background) and after (evoked) a series of pattern reversal visual stimuli. RESULTS: The elderly had a higher rate of background deflections at all electrode sites, but lower amplitudes at the occipital electrodes. The elderly had a lower rate of deflections during the period of evoked activity compared with the background period. The young had a higher degree of response deflection time locking and amplitude. The mean amplitude of the deflections recorded during the period of evoked activity was significantly greater in amplitude than the background deflections and greater than the amplitudes of the conventionally averaged VEP derived from the same data. Thus the lower amplitude VEPs seen in the elderly are due to their poor time locking and reduced amplification. Only 79% of the stimulus trials contributed deflections to the P1 response component in both young and elderly subjects and 63% to the N1. In young subjects, several of the new response parameters showed the presence of evoked response components that were not apparent in the conventionally averaged VEP derived from the same data. CONCLUSIONS: The novel methods presented here provide a great deal of additional information that is unavailable when analyzing data using only conventional evoked potential averaging.

Adolescent↗