Two microtubule-associated proteins required for anaphase spindle movement in Saccharomyces cerevisiae [published erratum appears in J Cell Biol 1995 Oct;131(2):561]

In many eucaryotic cells, the midzone of the mitotic spindle forms a distinct structure containing a specific set of proteins. We have isolated ASE1, a gene encoding a component of the Saccharomyces cerevisiae spindle midzone. Strains lacking both ASE1 and BIK1, which encodes an S. cerevisiae microtubule-associated protein, are inviable. The analysis of the phenotype of a bik1 ase1 conditional double mutant suggests that BIK1 and ASE1 are not required for the assembly of a bipolar spindle, but are essential for anaphase spindle elongation. The steady-state levels of Ase1p are regulated in a manner that is consistent with a function during anaphase: they are low in G1, accumulate to maximal levels after S phase and then drop as cells exit mitosis. Components of the spindle midzone may therefore be required in vivo for anaphase spindle movement. Additionally, anaphase spindle movement may depend on a dedicated set of genes whose expression is induced at G2/M.     

Building the bridge between animal movement and population dynamics

While the mechanistic links between animal movement and population dynamics are ecologically obvious, it is much less clear when knowledge of animal movement is a prerequisite for understanding and predicting population dynamics. GPS and other technologies enable detailed tracking of animal location concurrently with acquisition of landscape data and information on individual physiology. These tools can be used to refine our understanding of the mechanistic links between behaviour and individual condition through ‘spatially informed’ movement models where time allocation to different behaviours affects individual survival and reproduction. For some species, socially informed models that address the movements and average fitness of differently sized groups and how they are affected by fission–fusion processes at relevant temporal scales are required. Furthermore, as most animals revisit some places and avoid others based on their previous experiences, we foresee the incorporation of long-term memory and intention in movement models. The way animals move has important consequences for the degree of mixing that we expect to find both within a population and between individuals of different species. The mixing rate dictates the level of detail required by models to capture the influence of heterogeneity and the dynamics of intra- and interspecific interaction.     

Wnt3a-mediated chemorepulsion controls movement patterns of cardiac progenitors and requires RhoA function

The heart is the first organ to function during vertebrate development and cardiac progenitors are among the first cell lineages to be established. In the chick, cardiac progenitors have been mapped in the epiblast of pre-streak embryos, and in the early gastrula they are located in the mid-primitive streak, from which they enter the mesoderm bilaterally. Signals controlling the specification of cardiac cells have been well documented; however, migration routes of cardiac progenitors have not been directly observed within the embryo and the factor(s) controlling their movement are not known. In addition, it is not clear how cell movement is coordinated with cell specification in the early embryo. Here we use live imaging to show that cardiac progenitors migrate in highly directed trajectories, which can be controlled by Wnt3a. Ectopic Wnt3a altered movement trajectories and caused cardia bifida. This was rescued by electroporation of dominant-negative DN-Wnt3a into prospective cardiac cells. Explant essays and mutant analysis showed that cellular guidance involved repulsion in response to Wnt3a and required RhoA function. It has been shown that Wnt3a inhibits cardiogenic cell specification through a beta-catenin-dependent pathway. On the basis of our results, we propose that Wnt3a concomitantly guides the movement of cardiac progenitors by a novel mechanism involving RhoA-dependent chemorepulsion.     

Nerve growth factor signaling regulates motility and docking of axonal mitochondria

Axonal transport is thought to distribute mitochondria to regions of the neuron where their functions are required. In cultured neurons, mitochondrial transport responds to growth cone activity, and this involves both a transition between motile and stationary states of mitochondria and modulation of their anterograde transport activity. Although the exact cellular signals responsible for this regulation remain unknown, we recently showed that mitochondria accumulate in sensory neurons at regions of focal stimulation with NGF and suggested that this involves downstream kinase signaling. Here, we demonstrate that NGF regulation of axonal organelle transport is specific to mitochondria. Quantitative analyses of motility show that the accumulation of axonal mitochondria near a focus of NGF stimulation is due to increased movement into bead regions followed by inhibition of movement out of these regions and that anterograde and retrograde movement are differentially affected. In axons made devoid of F-actin by latrunculin B treatment, bidirectional transport of mitochondria continues, but they can no longer accumulate in the region of NGF stimulation. These results indicate that intracellular signaling can specifically regulate mitochondrial transport in neurons, and they suggest that axonal mitochondria can respond to signals by locally altering their transport behavior and by undergoing docking interactions with the actin cytoskeleton.     

Dharmo rakshati rakshitah : Hindutva movements in the UK

This article explores the relationship between Hindutva networks in the UK and the growth of Hindu nationalism in India since the 1980s. The article begins with a critique of ethnicity-based paradigms in sociological and anthropological disciplines and argues that they can share much epistemological space with ethnic and religious absolutist tendencies that have arisen in South Asian communities. It explores the ideological orientations that were required in the Hindutva movement to ‘make sense’ of Hindu migration and settlement in the West. Detailed discussions are presented of Hindutva views about the role of Hinduism in the global diaspora. The essay focuses on the structure and ideology of the Hindutva movement in the UK, tracing its origins to the patterns of indenture and early migration to east Africa, and looks at the impact of the Hindutva movement in the reorganization of youth and religious communities in the UK.     

Air movement preferences observed in naturally ventilated buildings in humid subtropical climate zone in China

Occupants’ preferences for air movement in naturally ventilated buildings have been extracted from a database of three thermal comfort surveys conducted in the humid subtropical climate zone in China, during winter, spring, and summer seasons. The distribution of draft sensation shows that only 25.7, 38.5, and 28.7% of the subjects in winter, spring, and summer, respectively, felt that the available air movement was just right, suggesting that indoor air velocity may be a big problem in naturally ventilated buildings in humid subtropical China. Air movement preferences show that 15.8, 61.3, and 80.6% of subjects in winter, spring, and summer, respectively, wanted more air movement. Only a handful of subjects wanted less air movement than they were actually experiencing in any season, suggesting that draft was not much of an issue for thermal comfort. Occupants’ preference for air movement is strongly related to thermal sensation, showing that people want to control air movement as a means of improving their comfort. The demand for less air movement under cool sensation is much smaller than the overwhelming demand for more air movement when the sensation was warm. The above results indicate that air movement might have a significant influence over the respondents’ comfort sensation and that people required a high level of air movement in order to be comfortable during the summer season. Thus, one efficient way to improve the thermal environment in summer in humid subtropical China could be to provide occupants with effective natural ventilation and allow personal control of the air movement. Our findings are also applicable to other buildings, to encourage designers to provide air movement as a low energy cooling strategy and to ensure that sufficient levels of air movement are available.     

Overview movement as an index of anesthetic depth in humans and experimental animals

Anesthesia is used widely in animal research, but there are diverse opinions regarding acceptable anesthetic depth. Excessive anesthesia is associated with increased morbidity and mortality. Traditionally, researchers have been taught that animal movement during surgical and experimental procedures indicates that the animal is 'underanesthetized.' Complex movement, however, can be initiated and propagated within the spinal cord, with little input from supraspinal structures. For example, frogs with high spinal-cord transections still maintain the wiping reflex, whereby the hindlimb can move to the forelimb to wipe away a noxious stimulus. Rats that have been decerebrated can perform complex tasks, such as grooming. Brain-dead humans can have spontaneous movement of the arms, legs, and head. Consistent with these phenomena, emerging evidence suggests that, in anesthetized animals, movement in response to noxious stimulation is abolished primarily via anesthetic action in the spinal cord. When isoflurane, halothane, or thiopental is delivered selectively to the brain circulation in goats, substantially greater anesthetic concentrations in brain are needed to ablate movement, as compared with those required upon delivery of anesthetic to the entire body. Rats that have had a precollicular decerebration require the same isoflurane concentrations to prevent movement as compared to intact rats. Furthermore, data from both humans and animals indicate that memory and awareness are ablated at anesthetic concentrations that are < 50% of those needed to abolish movement. Collectively, these data indicate that animals can be anesthetized at depths that, although they do not abolish movement, still produce unconsciousness and amnesia.     

Tobacco mosaic virus movement protein-mediated protein transport between trichome cells.

Tobacco mosaic virus movement protein (TMV MP) is required to mediate viral spread between plant cells via plasmodesmata. Plasmodesmata are cytoplasmic bridges that connect individual plant cells and ordinarily limit molecular diffusion to small molecules and metabolites with a molecular mass up to 1 kD. Here, we characterize functional properties of Nicotiana clevelandii trichome plasmodesmata and analyze their interaction with TMV MP. Trichomes constitute a linear cellular system and provide a predictable pathway of movement. Their plasmodesmata are functionally distinct from plasmodesmata in other plant cel types; they allow cell-to-cell diffusion of dextrans with a molecular mass up to 7 kD, and TMV MP does not increase this size exclusion limit for dextrans. In contrast, the 30-kD TMV MP itself moves between trichome cells and specifically mediates the translocation of a 90-kD beta-glucuronidase (GUS) reporter protein as a GUS::TMV MP fusion. Neither GUS by itself nor GUS in the presence of TMV MP moves between cells. These data imply that a plasmodesmal transport signal resides within TMV MP and is essential for movement. This signal confers selectivity to the translocated protein and cannot function in trans to support movement of other molecules.     

A Comparison of the Seasonal Movements of Tiger Sharks and Green Turtles Provides Insight into Their Predator-Prey Relationship

During the reproductive season, sea turtles use a restricted area in the vicinity of their nesting beaches, making them vulnerable to predation. At Raine Island (Australia), the highest density green turtle Chelonia mydas rookery in the world, tiger sharks Galeocerdo cuvier have been observed to feed on green turtles, and it has been suggested that they may specialise on such air-breathing prey. However there is little information with which to examine this hypothesis. We compared the spatial and temporal components of movement behaviour of these two potentially interacting species in order to provide insight into the predator-prey relationship. Specifically, we tested the hypothesis that tiger shark movements are more concentrated at Raine Island during the green turtle nesting season than outside the turtle nesting season when turtles are not concentrated at Raine Island. Turtles showed area-restricted search behaviour around Raine Island for ∼3–4 months during the nesting period (November–February). This was followed by direct movement (transit) to putative foraging grounds mostly in the Torres Straight where they switched to area-restricted search mode again, and remained resident for the remainder of the deployment (53–304 days). In contrast, tiger sharks displayed high spatial and temporal variation in movement behaviour which was not closely linked to the movement behaviour of green turtles or recognised turtle foraging grounds. On average, tiger sharks were concentrated around Raine Island throughout the year. While information on diet is required to determine whether tiger sharks are turtle specialists our results support the hypothesis that they target this predictable and plentiful prey during turtle nesting season, but they might not focus on this less predictable food source outside the nesting season.     

Ubiquitin-dependent sorting of integral membrane proteins for degradation in lysosomes

The pathways that deliver newly synthesized proteins that reside in lysosomes are well understood on comparison with our knowledge of how integral membrane proteins are sorted and delivered to the lysosome for degradation. Many membrane proteins are sorted to lysosomes following ubiquitination, which provides a sorting signal that can operate for sorting at the TGN (trans-Golgi network), at the plasma membrane or at the endosome for delivery into lumenal vesicles. Candidate multicomponent machines that can potentially move ubiquitinated integral membrane cargo proteins have been identified, but much work is still required to ascertain which of these candidates directly recognize ubiquitinated cargo and what they do with cargo after recognition. In the case of the machinery required for sorting into the lumenal vesicles of endosomes, other functions have also been determined including a link between sorting and movement of endosomes along microtubules.     

The Cik1/Kar3 motor complex is required for the proper kinetochore-microtubule interaction after stressful DNA replication

In budding yeast Saccharomyces cerevisiae, kinetochores are attached by microtubules during most of the cell cycle, but the duplication of centromeric DNA disassembles kinetochores, which results in a brief dissociation of chromosomes from microtubules. Kinetochore assembly is delayed in the presence of hydroxyurea, a DNA synthesis inhibitor, presumably due to the longer time required for centromeric DNA duplication. Some kinetochore mutants are sensitive to stressful DNA replication as these kinetochore proteins become essential for the establishment of the kinetochore-microtubule interaction after treatment with hydroxyurea. To identify more genes required for the efficient kinetochore-microtubule interaction under stressful DNA replication conditions, we carried out a genome-wide screen for yeast mutants sensitive to hydroxyurea. From this screen, cik1 and kar3 mutants were isolated. Kar3 is the minus-end-directed motor protein; Cik1 binds to Kar3 and is required for its motor function. After exposure to hydroxyurea, cik1 and kar3 mutant cells exhibit normal DNA synthesis kinetics, but they display a significant anaphase entry delay. Our results indicate that cik1 cells exhibit a defect in the establishment of chromosome bipolar attachment in the presence of hydroxyurea. Since Kar3 has been shown to drive the poleward chromosome movement along microtubules, our data support the possibility that this chromosome movement promotes chromosome bipolar attachment after stressful DNA replication.     

Orientation and Navigation in Elasmobranchs: Which Way Forward?

Elasmobranchs possess a multiplicity of mechanisms controlling posture and short distance orientation. Visual–vestibular contributions to posture and locomotion are well documented. So too, are the contributions of vision, olfaction and the octavolateralis senses to short distance orientation, particularly orientation to specific environmental stimuli such as those generated by prey. Less well understood are the mechanisms guiding orientation over longer distances. Anecdotal and systematic observations of behaviour show tidal, daily, repeat long distance, and even seasonal movement patterns. True navigation has not been demonstrated in elasmobranchs and the sensory mechanisms underlying the above movement patterns remain largely speculative. However, they are likely to include responses to water currents, and physical parameters such as temperature, pressure, and the geomagnetic field. Of particular interest in elasmobranchs is that geomagnetic orientation could be mediated directly via a magnetite based sensory system, or indirectly via the electrosensory system. Systematic studies of movement patterns and experimental studies of the underlying mechanisms of orientation are required to gain an increased understanding of orientation and navigation in this intriguing group.     

THE ROLE OF MICROTUBULES IN THE MOVEMENT OF PIGMENT GRANULES IN TELEOST MELANOPHORES

When microtubules in teleost melanophores are disrupted with antimitotic agents, colchicine, high hydrostatic pressure, low temperature, and vinblastine, the alignment and movement of the pigment granules in these cells disappear; during recovery, the return of alignment and movement corresponds in both time and space with the repolymerization of microtubules. Furthermore, analysis of nearest neighbor distances in untreated melanophores reveals that pigment granules are closely associated with microtubules. Other structures such as microfilaments, the endoplasmic reticulum, and the cytoplasmic matrix do not appear to be involved. Thus we conclude that microtubules determine the alignment and are essential for the selective movements of the pigment granules in these cells. Investigations of the mechanism of movement show that microtubules are required for both centrifugal and centripetal migrations and that they do not change in number or location during redistribution of pigment. Our results further indicate that microtubules in melanophores behave as semistable organelles as determined by investigation with colchicine and hydrostatic pressure. These observations and others rule out a push-pull mechanism based on the polymerization and depolymerization of microtubules or one which distinguishes two operationally different sets of microtubules. We propose instead that particles move by sliding along a fixed array of microtubules.     

First Passage Time Analysis of Animal Movement and Insights into the Functional Response

Movement plays a role in structuring the interactions between individuals, their environment, and other species. Although movement models coupled with empirical data are widely used to study animal distribution, they have seldom been used to study search time. This paper proposes first passage time as a novel approach for understanding the effect of the landscape on animal movement and search time. In the context of animal movement, first passage time is the time taken for an animal to reach a specified site for the first time. We synthesize current first passage time theory and derive a general first passage time equation for animal movement. This equation is related to the Fokker–Planck equation, which is used to describe the distribution of animals in the landscape. We illustrate the first passage time method by analyzing the effect of territorial behavior on the time required for a red fox to locate prey throughout its home range. Using first passage time to compute search times, we consider the effect of two different searching modes on a functional response. We show that random searching leads to a Holling type III functional response. First passage time analysis provides a new tool for studying how animal movement may influence ecological processes.     

A genetic determinant required for continuous reinfection of adjacent cells on large plasmid in S. flexneri 2a

We have identified a region (virG) on the 230 kb virulence plasmid of S. flexneri that is required for cell-to-cell spread of the bacterium. Tn5 insertions into this region result in avirulent mutants that can initially invade and multiply in epithelial cells, but tend to lose active movement and tend to localize within the cytoplasm, where they are gradually extinguished without infecting adjacent cells. The virG region was localized to within 4 kb and may contain a single cistron. Sequences hybridizing to this region were found in all intact virulence plasmids of Shigellae and enteroinvasive E. coli.     

Bves and NDRG4 regulate directional epicardial cell migration through autocrine extracellular matrix deposition

Directional cell movement is universally required for tissue morphogenesis. Although it is known that cell/matrix interactions are essential for directional movement in heart development, the mechanisms governing these interactions require elucidation. Here we demonstrate that a novel protein/protein interaction between blood vessel epicardial substance (Bves) and N-myc downstream regulated gene 4 (NDRG4) is critical for regulation of epicardial cell directional movement, as disruption of this interaction randomizes migratory patterns. Our studies show that Bves/NDRG4 interaction is required for trafficking of internalized fibronectin through the “autocrine extracellular matrix (ECM) deposition” fibronectin recycling pathway. Of importance, we demonstrate that Bves/NDRG4-mediated fibronectin recycling is indeed essential for epicardial cell directional movement, thus linking these two cell processes. Finally, total internal reflectance fluorescence microscopy shows that Bves/NDRG4 interaction is required for fusion of recycling endosomes with the basal cell surface, providing a molecular mechanism of motility substrate delivery that regulates cell directional movement. This is the first evidence of a molecular function for Bves and NDRG4 proteins within broader subcellular trafficking paradigms. These data identify novel regulators of a critical vesicle-docking step required for autocrine ECM deposition and explain how Bves facilitates cell-microenvironment interactions in the regulation of epicardial cell–directed movement.     

Assay for the transbilayer movement of polyisoprenoid-linked saccharides based on the transport of water-soluble analogues

Flippases are a class of membrane proteins that are proposed to facilitate the transbilayer movement of amphipathic polar lipids that are required for membrane biogenesis and the assembly of many diverse complex glycoconjugates in eukaryotic and prokaryotic cells. Despite their crucial roles in membrane biology, very little is known about their structures and the precise mechanism(s) by which they overcome the biophysical barriers of the hydrophobic core, and allow polar head groups to traverse membrane bilayers. This chapter presents methods based on the transport of water-soluble analogues that can be applied to investigate membrane proteins mediating the transverse diffusion of polyisoprenoid-linked glycolipid intermediates involved in the biosynthesis of N-linked glycoproteins, glycosylphosphatidylinositol anchors and bacterial polysaccharides.     

The role of extracellular materials in cell movement. I. Inhibition of mucopolysaccharide synthesis does not stop ruffling membrane activity or cell movement

The involvement of mucopolysaccharide synthesis in cell locomotion was investigated by determining the effects of inhibition of synthesis on ruffling membrane activity and cell movement by embryonic heart fibroblasts. Mucopolysaccharide synthesis was inhibited directly by treatment with a glutamine analog, 6-diazo-5-OXO-L-norleucine (DON), and indirectly with cycloheximide. DON treatment reduced synthesis to 20% of control values, and cycloheximide reduced synthesis to less than 10% of control values, as measured by incorporation of [35S]sulfate into mucopolysaccharides. Nevertheless, ruffling membrane activity and cell locomotion continued under both conditions. Cytochalasin B did not inhibit mucopolysaccharide synthesis, although it did stop ruffling and locomotion. These results suggest that if mucopolysaccharides are required for cell movement, they must have long half-lives or represent only a minute fraction of the normal synthetic load.