Opaque-white phenotype transition: a programmed morphological transition in Candida albicans.

This paper reports that the opaque and white phenotypes of Candida albicans constitute a true high-frequency reversible transition system. The rDNA restriction fragment and orthogonal field alternating gel electrophoresis profiles of opaque and white phenotypes are indistinguishable, and a genetic marker introduced into a white strain is present in all opaque derivatives of this strain. Opaque and white derivatives appear markedly different on a bismuth indicator medium and differ in a number of other respects. We have used bismuth medium to examine the spontaneous and temperature-induced frequencies of transition from opaque to white. The temperature-induced transition from opaque to white does not occur when opaque cells are held in water.     

Actin-based motility as a self-organized system: mechanism and reconstitution in vitro

Site-directed actin polymerisation in response to signalling is responsible for the formation of cell protrusions. These elementary 'actin-based motility processes' are involved in cell locomotion, cell metastasis, organ morphogenesis and microbial pathogenesis. We have reconstituted actin-based propulsive movement of particles of various sizes and geometries (rods, microspheres) in a minimum motility medium containing five pure proteins. The ATP-supported treadmilling of actin filaments, regulated by Actin Depolymerizing Factor (ADF/cofilin), profilin and capping proteins provides the thermodynamic basis for sustained actin-based movement. Local activation of Arp2/3 complex at the surface of the particle promotes autocatalytic barbed end branching of filaments, generating a polarized arborescent array. Barbed end growth of branched filaments against the surface generates a propulsive force and is eventually arrested by capping proteins. Understanding the mechanism of actin-based movement requires elucidation of the biochemical properties and mode of action of Arp2/3 complex in filament branching, in particular the role of ATP binding and hydrolysis in Arp2/3, and a physical analysis of the movement of functionalised particles. Because the functionalisation of the particle by an activator of Arp2/3 complex (N-WASP or the Listeria protein ActA) and the concentrations of effectors in the medium are controlled, the reconstituted motility assay allows an analysis of the mechanism of force production at the mesoscopic and molecular levels.     

Comparison of the respiratory transition at birth or hatching in viviparous and oviparous amniote vertebrates

Regardless of the mode of reproduction, three things must occur at birth or hatching in amniote vertebrates: initiation of breathing, pulmonary fluid elimination and reabsorption, and adequate perfusion of pulmonary circulation. Although data on these events are few, there appears to be no fundamental difference in them that can be associated with the oviparity to viviparity transition. There are, however, differences in the timing of these events in oviparous and viviparous amniotes. The transition to neonatal respiration tends to be very quick in viviparous species because the vascular support for oxygen uptake provided by the mother is rapidly disassociated from the mechanism for uptake by the embryo. By contrast, hatching often is a slow process, taking 24 h or more in some species, as chorioallantoic blood flow slowly gives way to clearing of the lungs and pulmonary gas exchange. Little is known of the mechanisms of pulmonary fluid elimination and reabsorption or lung inflation in reptiles, but the cellular structures and surfactant systems are similar in all amniote vertebrates. Nevertheless, there are differences, particularly of timing and maturation of various systems, but there has been no exploration of the functional (or phylogenetic) bases of these differences. Perfusion of the neonatal pulmonary system to support respiration in reptiles remains to be investigated. In mammals and birds, closure of the ductus arteriosus is important, but the role played by the ductus arterioisus in reptilian hatching or birth is not known.     

Diversity of temporal self-organized behaviors in a biochemical system.

The numerical study of a glycolytic model formed by a system of three delay-differential equations revealed a notable richness of temporal structures which included the three main routes to chaos, as well as a multiplicity of stable coexisting states. The Feigenbaum, intermitency and quasiperiodicity routes to chaos can emerge in the biochemical oscillator. Moreover, different types of birhythmicity, trirhythmicity and hard excitation emerge in the phase space. For a single range of the control parameter it can be observed the coexistence of two quasiperiodicity routes to chaos, the coexistence of a stable steady state with a stable torus, and the coexistence of a strange attractor with different stable regimes such as chaos with different periodic regimes, chaos with bursting behavior, and chaos with torus. In most of the numerical studies, the biochemical oscillator has been considered under periodic input flux being the mean input flux rate 6 mM/h. On the other hand, several investigators have observed quasiperiodic time patterns and chaotic oscillations by monitoring the fluorescence of NADH in glycolyzing yeast under sinusoidal glucose input flux. Our numerical results match well with these experimental studies.     

Nanoparticle-induced morphological transition of Bombyx mori nucleopolyhedrovirus: a novel method to treat silkworm grasserie disease

Grasserie, a polyorganotrophic disease caused by Bombyx mori nucleopolyhedrovirus (BmNPV), accounts for lethal infection to fifth instar silkworm larvae. It was found that nanoparticle (NP)-induced morphological transformation of BmNPV polyhedra could reduce the infectivity of BmNPV both in cell line and in silkworm larvae. Initially, 11 NPs were screened for evaluation of their nature of interaction with polyhedra surface through scanning electron microscopy. Amongst these NPs, lipophilically coated silica nanoparticle (SNPL), alumina nanoparticles in the hexagonal close-packed α structure and aspartate capped gold nanoparticle transformed polyhedra were tested for their infectivity in B. mori cell line using cytopathic effect and plaque reduction assay. SNPL was evaluated for its bio-efficacy in fifth instar silkworm larvae. The study of polyhedra morphology as a function of NP concentration showed severe ‘roughening’ of the polyhedra with replacement of the regular facets by a large number of irregular ones by SNPL, and this caused transition of highly infectious polyhedra into a nearly spherical, non-infectious structure. A moderate polyhedra roughening was observed for alumina NPs, and no roughening was noticed for gold NPs. The morphological changes could be correlated with reduction of virus-induced cytopathic effect and plaque formation, and increased survival rate of SNPL transformed polyhedra infected silkworm larvae to 70.09?±?6.61 % after 96 h. In this group, 61.04?±?8.03 % larvae formed normal cocoons from which moths eclosed, laid eggs and larvae emerged. This study could lead to open up newer pathways for designing nano pharmaceuticals to combat other viral diseases.     

Comparison of the respiratory transition at birth or hatching in viviparous and oviparous amniote vertebrates.

Regardless of the mode of reproduction, three things must occur at birth or hatching in amniote vertebrates: initiation of breathing, pulmonary fluid elimination and reabsorption, and adequate perfusion of pulmonary circulation. Although data on these events are few, there appears to be no fundamental difference in them that can be associated with the oviparity to viviparity transition. There are, however, differences in the timing of these events in oviparous and viviparous amniotes. The transition to neonatal respiration tends to be very quick in viviparous species because the vascular support for oxygen uptake provided by the mother is rapidly disassociated from the mechanism for uptake by the embryo. By contrast, hatching often is a slow process, taking 24 h or more in some species, as chorioallantoic blood flow slowly gives way to clearing of the lungs and pulmonary gas exchange. Little is known of the mechanisms of pulmonary fluid elimination and reabsorption or lung inflation in reptiles, but the cellular structures and surfactant systems are similar in all amniote vertebrates. Nevertheless, there are differences, particularly of timing and maturation of various systems, but there has been no exploration of the functional (or phylogenetic) bases of these differences. Perfusion of the neonatal pulmonary system to support respiration in reptiles remains to be investigated. In mammals and birds, closure of the ductus arteriosus is important, but the role played by the ductus arterioisus in reptilian hatching or birth is not known.     

BfCBR: a cannabinoid receptor ortholog in the cephalochordate Branchiostoma floridae (Amphioxus)

A gene encoding an ortholog of vertebrate CB(1)/CB(2) cannabinoid receptors was recently identified in the urochordate Ciona intestinalis (CiCBR; [Elphick, M.R., Satou, Y., Satoh, N., 2003. The invertebrate ancestry of endocannabinoid signalling: an orthologue of vertebrate cannabinoid receptors in the urochordate Ciona intestinalis. Gene 302, 95-101.]). Here a cannabinoid receptor ortholog (BfCBR) has been identified in the cephalochordate Branchiostoma floridae. BfCBR is encoded by a single exon and is 410 amino acid residue protein that shares 28% sequence identity with CiCBR and 23% sequence identity with human CB(1) and human CB(2). The discovery of BfCBR and CiCBR and the absence of cannabinoid receptor orthologs in non-chordate invertebrates indicate that CB(1)/CB(2)-like cannabinoid receptors originated in an invertebrate chordate ancestor of urochordates, cephalochordates and vertebrates. Furthermore, analysis of the relationship of BfCBR and CiCBR with vertebrate CB(1) and CB(2) receptors indicates that the gene/genome duplication that gave rise to CB(1) and CB(2) receptors occurred in the vertebrate lineage. Identification of BfCBR, in addition to CiCBR, paves the way for comparative analysis of the expression and functions of these proteins in Branchiostoma and Ciona, respectively, providing an insight into the ancestral functions of cannabinoid receptors in invertebrate chordates prior to the emergence of CB(1) and CB(2) receptors in vertebrates.     

The morphological and ontogenetic changes in the Protozoa during the transition to a sessile mode of life

The morphological adaptations of protozoans to sessile mode life and evolutionary changes in ontogeny are considered. There are main morphotypes of sessile protists: stalked organisms that attached to substrate by the extended base of body (basal disk), and unstalked organisms that are flatted on substrate. The origin of the morphotypes was independent in different taxa and involved nonhomologous structures. Adaptation to the sessile mode of life in the protists was connected with the progressive increase in the body size and intensity of organelle functions by polymerisation, subsequent division of function and change of functions. Evolution of adhesive organelles is characterised by growing intensity of their functions by allometric growth (usually without polymerisation), and in some cases with the subsequent division of functions and change of functions. The evolution manifests itself primarily in the organelles that provide interaction of cell with environment. The organelles that ensuring functioning of cell change due to correlations with the organelles of the first group. These two groups of organelles are similar to A.N. Sewertsoff's ecto- and endosomatic organs in multicellular organisms. The ontogeny of the sessile protists included three stages: formation of the migratory stage, distribution and choice of substrate and metamorphosis of the migratory stage after adhesion. As a rule there are no recapitulations on the first stage. The majority of structures tomotes or zoospores are inherited from the parent cell. Thus the present of some ancestral characteristics at the earlier stages of protistean ontogeny is display of the Baer's law. The main features of ontogeny evolution in sessile protists are the anaboly of the additional stages of life cycle, the displays of archallaxis or deviation during the migratory stage formation, and anaboly at the stage of buds morphogenesis after adhesion. At the last stage, the study of recapitulations is most perspective with the decision of phylogenetic problems in sessile protists.     

Metabolome analysis during the morphological transition of Candida albicans

Candida albicans is an opportunistic pathogen of humans with significant mortality in severely immunocompromised patients. The ability to switch from yeast to hyphal morphology and vice versa, in response to various environmental cues, is believed to be a critical virulence factor of this fungus. However, the mechanisms that recognize such environmental signals and trigger the morphological change at a system level are still not clearly understood. Therefore, we have compared the metabolite profiles of C. albicans cells growing under different hyphae-inducing conditions to the metabolite profiles of growing yeast cells. Surprisingly our results suggest an overall downregulation of cellular metabolism during the yeast to hyphal morphological transition. Among the metabolic pathways involved in the central carbon metabolism, we have found seventeen that were significantly downregulated in all three hyphae-inducing conditions. This indicates that these central carbon metabolic pathways are likely to be intrinsically involved in the downstream effects of the morphogenetic process.     

Origin of laurdan sensitivity to the vesicle-to-micelle transition of phospholipid-octylglucoside system: a time-resolved fluorescence study

The fluorescent probe laurdan has been shown to be sensitive to the vesicle-to-micelle transition of phosphatidylcholine/octylglucoside (M. Paternostre, O. Meyer, C. Grabielle-Madelmont, S. Lesieur, and, Biophys. J. 69:2476-2488). On the other hand, a study on the photophysics of laurdan in organic solvents has shown that the complex de-excitation pathway of the probe can be described by two successive processes, i.e., an intramolecular charge transfer followed by dielectric relaxation of the solvent if polar. These two excited-state reactions lead to three emitting states, i.e., a locally excited state, a charge transfer state, and a solvent relaxed state (M. Viard, J. Gallay, M. Vincent, B. Robert and, Biophys. J. 73:2221-2234). Experiments have been performed using time-resolved fluorescence on the probe inserted in amphiphile aggregates (mixed liposomes, mixed micelles) different in detergent-to-lipid ratios. The results have been compared with those obtained for laurdan inserted in dipalmitoyl phosphatidylcholine liposomes in the gel and in the fluid lamellar phase. Except for laurdan in dipalmitoyl phosphatidylcholine liposomes in the gel lamellar phase, the red part of the emission spectra originates from the de-excitation of the relaxed excited state of laurdan, indicating that indeed the dielectric relaxation process is an important phenomena in the ground-state return pathway of this probe. On the other hand, the maximization entropy method (MEM) analysis of the fluorescence decay recorded in the blue part of the emission spectra indicates that the dielectric relaxation is not the only reaction occurring to the excited state of laurdan. Moreover, the analysis of the fluorescence decays of laurdan inserted in gel lamellar dipalmitoylphosphatidylcholine (DPPC) liposomes indicates excited-state reactions, although dielectric relaxation is impossible. These results are in agreement with the de-excitation pathway determined from laurdan behavior in organic solvent even if, in most of the aggregates studied in this work, the major phenomenon is the dielectric relaxation of the solvent. All along the vesicle-to-micelle transition, we have observed that the lifetime of the relaxed excited state of laurdan continuously decreases probably due to a dynamic quenching process by water molecules. On the other hand, the time constant of the dielectric relaxation process remains almost unchanged in the lamellar part of the transition but abruptly decreases as soon as the first mixed micelle is formed. This decrease is continuous all over the rest of the transition even if it is more pronounced in the mixed liposomes' and mixed micelles' coexistence. The increase of the octylglucoside-to-lipid ratio of the mixed micelles via the change of the size and the shape of the aggregates may facilitate the penetration and the mobility of water molecules. Therefore, during the vesicle-to-micelle transition, laurdan probes the evolution of both the amphiphile packing in the aggregates and the increase of the interface polarity. This study finally shows that the detergent-to-lipid ratio of the mixed micelles is an important parameter to control to limit the penetration and the mobility of water within the amphiphile aggregates and that laurdan is a nice tool to monitor this phenomenon.     

Induced life cycle transition from holocycly to anholocycly of the Russian wheat aphid (Homoptera: Aphididae)

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko),exists with holocyclic life cycle in Tacheng, Xinjiang in Northwest China. It produces males and oviparae to mate and oviposit for overwintering by eggs. Under laboratory conditions with 14 h/d photophase and temperature not lower than 15℃, RWA occurred in parthenogenesis and produced no males. The laboratory popu-lations of Russian wheat aphid, which were kept under natural conditions in fall by 15th, 49th and 81st generation while wild populations produced males and oviparae for mating, produced males and oviparae with their number decreased gradually, but viviparae and nymphs increased sequen-tially. As a result, it produced a small amount of oviparae and no males emerged in fields by 49 generations' reproduction in laboratory. After development of 81 generations, oviparae happened occasionally and no eggs occurred for overwintering instead of viviparae and nymphs. A hypothesis of RWA disastrous process was proposed. The life cycle of RWA can be changed from holocycly to anholocycly in its long-term spread and evolution. Anholocycly is more dangerous than holocycly to small grains for its strong adaptability and dispersal ability.     

Spatial glass transition temperature variations in polymer glass: application to a maltodextrin-water system

A model was developed to predict spatial glass transition temperature (T(g)) distributions in glassy maltodextrin particles during transient moisture sorption. The simulation employed a numerical mass transfer model with a concentration dependent apparent diffusion coefficient (D(app)) measured using Dynamic Vapor Sorption. The mass average moisture content increase and the associated decrease in T(g) were successfully modeled over time. Large spatial T(g) variations were predicted in the particle, resulting in a temporary broadening of the T(g) region. Temperature modulated differential scanning calorimetry confirmed that the variation in T(g) in nonequilibrated samples was larger than in equilibrated samples. This experimental broadening was characterized by an almost doubling of the T(g) breadth compared to the start of the experiment. Upon reaching equilibrium, both the experimental and predicted T(g) breadth contracted back to their initial value.     

Dynamic study of the transition from hyaluronan- to integrin-mediated adhesion in chondrocytes

Membrane-bound hyaluronan mediates the initial adhesive interactions between many cell types and external surfaces. In RCJ-P chondrocytes, such early contacts are mediated through a thick hyaluronidase-sensitive coat. The early adhesion is followed by integrin-mediated interactions and the formation of stable focal adhesions. During this process, the distance between the cell membrane and the surface is reduced from micrometers to few tens of nanometers. The transition from hyaluronan- to integrin-mediated adhesion was studied on glass surfaces by total internal reflection fluorescence microscopy. Hyaluronan-mediated adhesion precedes focal adhesions formation by 2-10 min. After these initial interactions, the pericellular hyaluronan remains sequestered into discrete pockets between the cell and the surface, which are a few hundreds nanometers thick and a few micrometers wide, and are flanked by focal adhesions. The hyaluronan coat facilitates the nucleation of small paxillin-rich contacts, which later mature into focal adhesions. These dynamic studies demonstrate that pericellular hyaluronan mediates initial cell-surface adhesion, and regulates the formation of focal adhesions.     

Specific guidance of motor axons to duplicated muscles in the developing amniote limb

The effect of alteration of limb pattern upon motor axon guidance has been investigated in chick embryos. Following grafting of the zone of polarizing activity (ZPA) into the anterior margin of the early limb bud, limbs develop with forearms duplicated about the anteroposterior axis. The position of motoneurones innervating the duplicated posterior forearm extensor EMU was mapped by retrograde transport of horse radish peroxidase (HRP). The motor pool labelled from injection into the anteriorly duplicated EMU muscle is consistently similar to that supplying the posterior EMU muscle on the unoperated side of the embryo. In those cases where the axons are well filled, their trajectories from the injection site are observed to change position within the radial nerve to specifically innervate the duplicated muscle. The axons modify their trajectories proximal to the level of limb duplication in a region where there is no change in the pattern of overt differentiation of the limb cells. This suggests that axons may use a cell's positional value to navigate and provides significant support for the theory of positional information.     

Individuation in Sorghum bicolor: a self-organized process involved in physiological adaptation to salinity

In Sorghum bicolor, salt-adaptation was defined as the capacity of plants to grow at 300 m M NaCl (a lethal concentration) following a 3-week pre-treatment with 150 m M NaCl (a sublethal concentration). Large populations induced for salt-adaptation were analysed. Two modes of osmotic regulation (Na-includer and Na-excluder) were differentiated during induction of salt-adaptation, in spite of the genetic and environmental homogeneity. This variability was not related to any incapacity of the Na-includers to control accumulation of Na ⁺ ions in the shoot, because most of the pre-treated plants displayed a similar capacity of growth and control of Na ⁺ uptake after transfer to 300 m M NaCl. This unsuspected complexity of initially homogeneous populations points on the inadequacy of physiological studies focused on the ‘average individual’. Further analyses showed that variability was not directly related to micro-environmental variations. It is concluded that a process of individuation is caused by a third source of variability, which is the expression of a self-organizing process normally occurring during the transition phases in development. In constraining environments, this phenomenon of individuation includes adaptive modifications.