Distribution and characterization of peroxisomes in Arabidopsis by visualization with GFP: dynamic morphology and actin-dependent movement

Peroxisomes were visualized in living cells of various tissues in transgenic Arabidopsis by green fluorescent protein (GFP) through the addition of the peroxisomal targeting signal 1 (PTS1) or PTS2. The observation using confocal laser scanning microscopy revealed that the GFP fluorescence signals were detected as spherical spots in all cells of two kinds of transgenic plants. Immunoelectron microscopic analysis using antibodies against the peroxisomal marker protein, catalase, showed the presence of GFP in peroxisomes, confirming that GFP was correctly transported into peroxisomes by PTS1 or PTS2 pathways. It has been also revealed that peroxisomes are motile organelles whose movement might be caused by cytoplasmic flow. The movement of peroxisomes was more prominent in root cells than that in leaves, and divided into two categories: a relatively slow, random, vibrational movement and a rapid movement. Treatment with anti-actin and anti-tubulin drugs revealed that actin filaments involve in the rapid movement of peroxisomes. Moreover, abnormal large peroxisomes are present as clusters at the onset of germination, and these clusters disappear in a few days. Interestingly, tubular peroxisomes were also observed in the hypocotyl. These findings indicate that the shape, size, number and movement of peroxisomes in living cells are dynamic and changeable rather than uniform.     

Extracellular matrix-mediated tissue remodeling following axial movement of teeth.

Tooth eruption is a multifactorial process involving movement of existing tissues and formation of new tissues coordinated by a complex set of genetic events. We have used the model of the unopposed rodent molar to study morphological and genetic mechanisms involved in axial movement of teeth. Following extraction of opposing upper molars, lower molars supererupted by 0.13 mm. Labeled tissue sections revealed significant amounts of new bone and cementum apposition at the root apex of the unopposed side following supereruption for 12 days. Newly apposited cementum and alveolar bone layers were approximately 3-fold thicker in the experimental vs the control group, whereas periodontal ligament width was maintained. Tartrate-resistant acid phosphatase staining indicated bone resorption at the mesial alveolar walls of unopposed molars and provided in tandem with new bone formation at the distal alveolar walls an explanation for the distal drift of molars in this model. Microarray analysis and semiquantitative RT-PCR demonstrated a significant increase in collagen I, integrin beta5, and SPARC gene expression as revealed by comparison between the unopposed molar group and the control group. Immunohistochemical verification revealed increased levels of integrin beta5 and SPARC labeling in the periodontal ligament of the unopposed molar. Together our findings suggest that posteruptive axial movement of teeth was accomplished by significant formation of new root cementum and alveolar bone at the root apex in tandem with upregulation of collagen I, integrin beta5, and SPARC gene expression.     

Functional Asymmetry at Evaluation of Movement Trajectory of the Solid Sound Image in Human

At studying localization by human of moving solid sound image (SSI) under conditions of dichotic stimulation, an asymmetry has been revealed in evaluation of a shift of the initial and final points of the opposite SSI movement under mirror-symmetry conditions of stimulation. The shift to the right in all cases exceeds that to the left (by 3.4–32.1 degrees). The most pronounced asymmetry is observed at the initial moment of the SSI movement at the synergism of interaural differences in stimulation by its time and intensity; under these conditions, the trajectory of the SSI movement to the left turns out to be about 1.8 times longer than the movement to the right. Possible neurophysiological mechanisms of the obtained results are considered.     

Peculiarities of adaptive behavior of mangrove molluscs at the Guinea coast

Orientation behavior of two species of littoral molluscs inhabiting mangrove brushwoods at the Guinea coast is studied under field and laboratory conditions. It is shown that Littorina angulifera able to breath air demonstrates a selective movement in the vertical direction upwards from the water surface to the rhizophlora crown. The partial bilateral extirpation of head feelers did not disturb the revealed orientation. The Tympanotus fuscatus inhabiting the slit ground has a tendency for agglomeration. The molluscs transferred at the distance up to 50 cm from the agglomeration try to return to it. The revealed reaction was confirmed by experiments in labyrinth. Extirpation of distal parts of head feelers reduced statistically significantly the orientation ability of the animals. Using video recording, a change of the mollusc movement rate in the labyrinth during orientation towards their conspecific clusters is shown. The biological significance and possible physiological mechanisms of the revealed reactions are discussed.     

Long-distance movement factor: a transport function of the potyvirus helper component proteinase.

Transport of viruses from cell to cell in plants typically involves one or more viral proteins that supply dedicated movement functions. Transport from leaf to leaf through phloem, or long-distance transport, is a poorly understood process with requirements differing from those of cell-to-cell movement. Through genetic analysis of tobacco etch virus (TEV; potyvirus group), a novel long-distance movement factor was identified that facilitates vascular-associated movement in tobacco. A mutation in the central region of the helper component proteinase (HC-Pro), a TEV-encoded protein with previously described activities in aphid-mediated transmission and polyprotein processing, inactivated long-distance movement. This mutant virus exhibited only minor defects in genome amplification and cell-to-cell movement functions. In situ histochemical analysis revealed that the mutant was capable of infecting mesophyll, bundle sheath, and phloem cells within inoculated leaves, suggesting that the long-distance movement block was associated with entry into or exit from sieve elements. The long-distance movement defect was specifically complemented by HC-Pro supplied in trans by a transgenic host. The data indicate that HC-Pro functions in one or more steps unique to long-distance transport.     

The ribosome as a molecular machine: the mechanism of tRNA-mRNA movement in translocation

Translocation of tRNA and mRNA through the ribosome is one of the most dynamic events during protein synthesis. In the cell, translocation is catalysed by EF-G (elongation factor G) and driven by GTP hydrolysis. Major unresolved questions are: how the movement is induced and what the moving parts of the ribosome are. Recent progress in time-resolved cryoelectron microscopy revealed trajectories of tRNA movement through the ribosome. Driven by thermal fluctuations, the ribosome spontaneously samples a large number of conformational states. The spontaneous movement of tRNAs through the ribosome is loosely coupled to the motions within the ribosome. EF-G stabilizes conformational states prone to translocation and promotes a conformational rearrangement of the ribosome (unlocking) that accelerates the rate-limiting step of translocation: the movement of the tRNA anticodons on the small ribosomal subunit. EF-G acts as a Brownian ratchet providing directional bias for movement at the cost of GTP hydrolysis.     

Conversion in the requirement of coat protein in cell-to-cell movement mediated by the cucumber mosaic virus movement protein

Plant viruses have movement protein (MP) gene(s) essential for cell-to-cell movement in hosts. Cucumber mosaic virus (CMV) requires its own coat protein (CP) in addition to the MP for intercellular movement. Our present results using variants of both CMV and a chimeric Brome mosaic virus with the CMV MP gene revealed that CMV MP truncated in its C-terminal 33 amino acids has the ability to mediate viral movement independently of CP. Coexpression of the intact and truncated CMV MPs extremely reduced movement of the chimeric viruses, suggesting that these heterogeneous CMV MPs function antagonistically. Sequential deletion analyses of the CMV MP revealed that the dispensability of CP occurred when the C-terminal deletion ranged between 31 and 36 amino acids and that shorter deletion impaired the ability of the MP to promote viral movement. This is the first report that a region of MP determines the requirement of CP in cell-to-cell movement of a plant virus.     

Change in the actin cytoskeleton during seismonastic movement of Mimosa pudica

The seismonastic movement of Mimosa pudica is triggered by a sudden loss of turgor pressure. In the present study, we compared the cell cytoskeleton by immunofluorescence analysis before and after movement, and the effects of actin- and microtubule-targeted drugs were examined by injecting them into the cut pulvinus. We found that fragmentation of actin filaments and microtubules occurs during bending, although the actin cytoskeleton, but not the microtubules, was involved in regulation of the movement. Transmission electron microscopy revealed that actin cables became loose after the bending. We injected phosphatase inhibitors into the severed pulvinus to examine the effects of such inhibitors on the actin cytoskeleton. We found that changes in actin isoforms, fragmentation of actin filaments and the bending movement were all inhibited after injection of a tyrosine phosphatase inhibitor. We thus propose that the phosphorylation status of actin at tyrosine residues affects the dynamic reorganization of actin filaments and causes seismonastic movement.     

Eye movements in Daphnia pulex (De Geer).

1. The various types of eye movement exhibited by the cyclopean eye of Daphnia pulex were studied using high speed motion photography. 2. This rudimentary eye, which consists of only 22 ommatidia, can move through approximately 150 degrees in the sagittal plane and 60 degrees in the horizontal plane. 3. Four classes of eye movement were found: (1) a high speed tremor at 16 Hz with an amplitude of 3-4 degrees, which resembles physiological nystagmus, (2) a slow rhythmic scanning movement at 4 Hz, and 5-6 degrees amplitude, (3) large fast eye movements similar to saccadic eye movements and (4) optokinetic nystagmus produced by moving striped patterns. 4. Where the fast tremor occurred concurrently with the slow rhythmic scan, a Fourier analysis revealed that the former was the fourth harmonic of the latter.     

Specification of neurepithelium and surface epithelium in avian transplantation chimeras

Previous studies of the avian blastoderm have revealed that extensive displacements occur within the epiblast during gastrulation and neurulation. The present study had two main purposes: (1) to map the origin and movement of prospective surface epithelial cells, and (2) to ask whether neurepithelial and surface epithelial cell fates are determined prior to cell movement, or whether they arise later as a result of the ultimate position attained by cells through their movement. Our results show that the rostral and lateral intraembryonic and extraembryonic surface epithelium originates as far laterally as at the area pellucida-area opaca interface of the early epiblast. Intraembryonic surface epithelial cells rearrange relative to one another, extending medially to contribute to the formation of the neural folds, whereas extraembryonic surface epithelial cells maintain their lateral positions, spreading uniformly as the epiblast expands. Our results further show that surface epithelial and neurepithelial cell fates are labile at the onset of neurulation, suggesting that cell fate is specified following cell movement.     

The Role of Human Transportation Networks in Mediating the Genetic Structure of Seasonal Influenza in the United States

Recent studies have demonstrated the importance of accounting for human mobility networks when modeling epidemics in order to accurately predict spatial dynamics. However, little is known about the impact these movement networks have on the genetic structure of pathogen populations and whether these effects are scale-dependent. We investigated how human movement along the aviation and commuter networks contributed to intra-seasonal genetic structure of influenza A epidemics in the continental United States using spatially-referenced hemagglutinin nucleotide sequences collected from 2003–2013 for both the H3N2 and H1N1 subtypes. Comparative analysis of these transportation networks revealed that the commuter network is highly spatially-organized and more heavily traveled than the aviation network, which instead is characterized by high connectivity between all state pairs. We found that genetic distance between sequences often correlated with distance based on interstate commuter network connectivity for the H1N1 subtype, and that this correlation was not as prevalent when geographic distance or aviation network connectivity distance was assessed against genetic distance. However, these patterns were not as apparent for the H3N2 subtype at the scale of the continental United States. Finally, although sequences were spatially referenced at the level of the US state of collection, a community analysis based on county to county commuter connections revealed that commuting communities did not consistently align with state geographic boundaries, emphasizing the need for the greater availability of more specific sequence location data. Our results highlight the importance of utilizing host movement data in characterizing the underlying genetic structure of pathogen populations and demonstrate a need for a greater understanding of the differential effects of host movement networks on pathogen transmission at various spatial scales.     

Rational analyses of organelle trajectories in tobacco pollen tubes reveal characteristics of the actomyosin cytoskeleton

To gain insight into the characteristics of organelle movement and the underlying actomyosin motility system in tobacco pollen tubes, we collected data points representing sequential organelle positions in control and cytochalasin-treated cells, and in a sample of extruded cytoplasm. These data were utilized to reconstruct approximately 900 tracks, representing individual organelle movements, and to produce a quantitative analysis of the movement properties, supported by statistical tests. Each reconstructed track appeared to be unique and to show irregularities in velocity and direction of movement. The regularity quotient was near 2 at the tip and above 3 elsewhere in the cell, indicating that movement is more vectorial in the tube area. Similarly, the progressiveness ratio showed that there were relatively more straight trajectories in the tube region than at the tip. Consistent with these data, arithmetical dissection revealed a high degree of randomlike movement in the apex, lanes with tip-directed movement along the flanks, and grain-directed movement in the center of the tube. Intercalated lanes with bidirectional movement had lower organelle velocity, suggesting that steric hindrance plays a role. The results from the movement analysis indicate that the axial arrangement of the actin filaments and performance of the actomyosin system increases from tip to base, and that the opposite polarity of the actin filaments in the peripheral (+-ends of acting filaments toward the tip) versus the central cytoplasm (+-ends of actin filaments toward to the grain) is installed within a few minutes in these tip-growing cells.     

Movement of the iron-sulfur subunit beyond the ef loop of cytochrome b is required for multiple turnovers of the bc1 complex but not for single turnover Qo site catalysis.

Recent kinetics experiments using mutants of the bc(1) complex (ubihydroquinone-cytochrome c oxidoreductase) iron-sulfur subunit with modified hinge regions have revealed the crucial role played by the large scale movement of its [2Fe-2S] cluster domain during the activity of this enzyme. In particular, one of these mutants (+1Ala) with an insertion of one alanine residue in the hinge region is partially deficient in performing this movement. We found that this defect can be overcome by the appearance of a second mutation substituting the leucine at position 286 in the ef loop of cytochrome b with a phenylalanine. Detailed studies of these mutants and their derivatives revealed that the ef loop acts as a barrier that needs to be crossed for multiple turnovers of the enzyme but not for a single turnover ubihydroquinone oxidation site catalysis. These findings indicate that the movement of the iron-sulfur subunit is composed of two discrete parts: a "micro-movement" at the cytochrome b interface, during which the [2Fe-2S] cluster interacts with ubihydroquinone oxidation site occupants and catalyzes ubihydroquinone oxidation, and a "macro-movement," during which the cluster domain swings away from cytochrome b interface, crosses the ef loop, and reaches a position close to cytochrome c(1) heme, to which it ultimately transfers an electron.     

Nuclear positioning: dynein needed for microtubule shrinkage-coupled movement

Nuclear movement often requires interactions between the cell cortex and microtubules. A new study has revealed a novel protein interaction linking microtubule plus-ends with the cortex and a role for dynein in microtubule shrinkage-coupled movement.     

Regional movements of satellite‐tagged whale sharks Rhincodon typus in the Gulf of Aden

To gain insight into whale shark (Rhincodon typus) movement patterns in the Western Indian Ocean, we deployed eight pop‐up satellite tags at an aggregation site in the Arta Bay region of the Gulf of Tadjoura, Djibouti in the winter months of 2012, 2016, and 2017. Tags revealed movements ranging from local‐scale around the Djibouti aggregation site, regional movements along the coastline of Somaliland, movements north into the Red Sea, and a large‐scale (>1,000 km) movement to the east coast of Somalia, outside of the Gulf of Aden. Vertical movement data revealed high occupation of the top ten meters of the water column, diel vertical movement patterns, and deep diving behavior. Long‐distance movements recorded both here and in previous studies suggest that connectivity between the whale sharks tagged at the Djibouti aggregation and other documented aggregations in the region are likely within annual timeframes. In addition, wide‐ranging movements through multiple nations, as well as the high use of surface waters recorded, likely exposes whale sharks in this region to several anthropogenic threats, including targeted and bycatch fisheries and ship‐strikes. Area‐based management approaches focusing on seasonal hotspots offer a way forward in the conservation of whale sharks in the Western Indian Ocean.     

The plant cell nucleus is constantly alert and highly sensitive to repetitive local mechanical stimulations

When mechanical stimulation is applied to a plant cell, the nucleus usually shows oriented movement to the site of stimulation (as a defensive response). Former researchers have revealed that applying mechanical pressure to plant tissues could line up cell division plane. A proposal, therefore, was put forward that cells inside plant tissue could receive mechanical signals from their growing neighbors to adjust their nuclear position and thus regulate the orientation of their dividing plane in order to form characteristic morphology of plant organs. To explore nuclear capacity and sensitivity to rapidly changing signals, multiple mechanical stimulations were applied to the same plant cell at intervals, either locally or at distance. The results revealed that the nucleus was highly sensitive to mechanical stimulations. It responded quickly to both local and distant stimulation by showing oriented movement toward the stimulation site. The nucleus was able to respond immediately to a second stimulation (no time lag) by starting up a second oriented movement toward the new signal; the completion of nuclear oriented movement to a first site of stimulation was not necessary for startup of a subsequent movement track to a second stimulation site, regardless of whether the second stimulation was applied ahead of or behind the moving nucleus. The nucleus responded to a second stimulation without loss of velocity, whether or not it was in a resting or moving state. This novel finding favors the proposal that growing tissues adjust the location of nuclei in cells by varying mechanical pressures; they thus control cell division according to a plan whereby organs and their constituent tissues develop in an orderly, specified manner. It appears that the enhanced sensitivity of plant cells to mechanical pressure is necessary not only in response to the external environment, but also to the developmental microenvironment inside the tissues.     

A quantitative approach to understand the ultramicro-structure responsible for input mechanism in excitation-contraction (E-C) coupling, on the basis of physio-morphological observations]

Our morphophysiological studies using concanavalin A-ferritin (Con A-F) have indicated that: (1) an out- and up-ward movement of a movable structure at the luminal surface-portion of the T-tubular membrane opposite the feet initiates contraction; (2) the grade of the movement depends on that of depolarization; (3) the movable structure is essentially a 'moving arm', which is fixed in wall of T-tubules at its fixed end and is able to be bound to the Con A-moiety of Con A-F particle about at its free end. Calculation based on molecular morphology and behaviour of Con A-F particle revealed following points: If (a) the origin of coordinate be the intersection of longitudinal center line of foot and the surface of T-tubular membrane in the transverse section of the tubules, (b) the fixed point of the arm is exactly on the surface of T-tubular membrane, and (c) the movement takes place in the transverse direction to the longitudinal axis of T-tubules, (1) the location of the center point of the movement of the moving arm is at 5.4 nm in the outside direction from the origin, (2) the arm is about 4 nm in length and moves by about 2.4 nm up- and out-ward at its free end upon about complete depolarization.     

Replication and discrimination of limb movement velocity

It is well known that proprioception is composed of the senses of movement and position. Whereas tests of position sense are quite commonly used, tests of the acuity in perception of movement velocity are scarce. In the present study we examined some novel tests for assessing the sense of limb movement velocity, involving replication and discrimination of single-joint movement velocity. Specifically, we investigated: (1) whether replication of limb movement velocity is more accurate following active criterion movements as compared to passive; (2) whether antagonist muscle contraction during passive limb movement enhances velocity discrimination; (3) how criterion movement velocity influences response accuracy; (4) the relationship between movement velocity and movement extent during velocity replication; and (5) whether subjects really base discrimination of velocities on perceived velocity. Sixteen healthy subjects participated in four tests (I-IV). For each test, horizontal abductions were performed about the right glenohumeral joint from the sagittal plane. The subjects were required to actively replicate the velocity of either an active (Test I) or passive (Test II) criterion movement, or judge whether a passive/semipassive (passive during antagonist muscle contraction) movement was faster or slower than a previous passive/semipassive criterion movement (Test III/IV). The results revealed higher response accuracy for Test I compared to Test II and for slower movements compared to faster, but no difference in response accuracy between Test III and IV. For velocity discrimination, the analysis revealed that the subjects based their judgment on the difference between criterion and comparison velocity rather than time or extent cues.