Sensory Machinery Research Articles

Surface Sensing and Settlement Strategies of Marine Biofouling Organisms

This review article summarizes some recent insights into the strategies used by marine organisms to select surfaces for colonization. While larger organisms rely on their sensory machinery to select surfaces, smaller microorganisms developed less complex but still effective ways to probe interfaces. Two examples, zoospores of algae and barnacle larvae, are discussed and both appear to have build-in test mechanisms to distinguish surfaces with different physicochemical properties. Some systematic studies on the influence of surface cues on exploration, settlement and adhesion are summarized. The intriguing notion that surface colonization resembles a parallelized surface sensing event is discussed towards its complementarity with conventional surface analytical tools. The strategy to populate only selected surfaces seems advantageous as waves, currents and storms constantly challenge adherent soft and hard fouling organism.

Generalized Movement Strategies for Constrained Consumers: Ignoring Fitness Can Be Adaptive

Abstract Movements made by real organisms--such as movements involved in dispersal, migration, and habitat selection--are expected to occasionally be suboptimal because of realistic constraints imposed by incomplete information, perceptual limitations, and stochasticity. Previous theory considering such constraints has shown that movements appropriately conditioned on habitat or resource characteristics can balance out suboptimal components of movement and thereby lead organisms to ideal free distributions and fitness maxima, whereas movements conditioned on fitness differentials cannot. These findings suggest a somewhat paradoxical hypothesis: even if organisms have information about their fitness, movement strategies that maximize fitness may be conditioned on something other than fitness per se. We test this hypothesis by investigating the evolutionary stability of generalized, conditional movement strategies that vary in their use of information on fitness versus information on habitat characteristics. We show that when costs of sensory machinery are included, natural selection should favor movement strategies that completely ignore fitness information. Finally, we synthesize previous work by showing how several previous important theoretical results for adaptive movement strategies are united under our one general model.

Developmental plasticity and the evolution of parasitism in an unusual nematode, Parastrongyloides trichosuri.

BackgroundParasitism is an important life history strategy in many metazoan taxa. This is particularly true of the Phylum Nematoda, in which parasitism has evolved independently at least nine times. The apparent ease with which parasitism has evolved amongst nematodes may, in part, be due to a feature of nematode development acting as a pre-adaptation for the transition from a free-living to a parasitic life history. One candidate pre-adaptive feature for evolution in terrestrial nematodes is the dauer larva, a developmentally arrested morph formed in response to environmental signals.ResultsWe investigated the role of dauer development in the nematode, Parastrongyloides trichosuri, which has retained a complete free-living life cycle in addition to a life cycle as a mammalian gastrointestinal parasite. We show that the developmental switch between these life histories is sensitive to the same environmental cues as dauer arrest in free-living nematodes, including sensitivity to a chemical cue produced by the free-living stages. Furthermore, we show that genetic variation for the sensitivity of the cue(s) exists in natural populations of P. trichosuri, such that we derived inbred lines that were largely insensitive to the cue and other lines that were supersensitive to the cue.ConclusionsFor this parasitic clade, and perhaps more widely in the phylum, the evolution of parasitism co-opted the dauer switch of a free-living ancestor. This lends direct support to the hypothesis that the switch to developmental arrest in the dauer larva acted as a pre-adaptation for the evolution of parasitism, and suggests that the sensory transduction machinery downstream of the cue may have been similarly co-opted and modified.

How stochastic adaptation of neurons shapes interspike interval statistics – theory and experiment

Trial-to-trial variability of neuronal responses is a prominent feature of sensory systems and has a significant impact on subsequent sensory signal processing. Fluctuations of the underlying ionic currents due to channel noise represent a major intrinsic source of noise that causes neuronal response variability. In many sensory systems it is, however, difficult to assess the type of channel noise by direct somatic recordings without severely damaging the sensory transduction machinery. Here we develop a novel indirect approach to distinguish different types of noise based on the interspike interval (ISI) statistics. The method is then used to determine the dominating source of noise of a sensory neuron. In particular, we seek to distinguish noise originating from fast spike-generating channels from channel noise associated to slow adaptation currents. Adaptation currents are found in many neurons and profoundly shape the signal transmission properties

Homosexual Pairing within a Swarm-Based Mating System: The Case of the Chironomid Midge

Homosexuality has been dubbed the Darwinian paradox, because it raises the question of how behaviour that would seem to reduce the chance of successful mating can be maintained by natural selection. This question rests on the assumption that same sex mating is the result of active choice of partner, hardwired into the mating behaviour, but there is an alternative explanation for such behaviour. I refer to the possibility that same-sex mating is the result, not of adaptive behaviour at all, but rather of errors due to imprecise sensory machinery. Such an explanation finds support within the mating system of insects with swarm-based mating systems. To explore this case, I turn to the common chironomid midge. I show that homosexual pairing here, exclusively involving male/male pairs, is common. I attempt to show that this observation, together with data on insect predators of swarming midges, can be used to penetrate the mysteries of this fascinating but elusive mating system.

Functional implications of sterol transport by the oxysterol-binding protein gene family

Cholesterol and its numerous oxygenated derivatives (oxysterols) profoundly affect the biophysical properties of membranes, and positively and negatively regulate sterol homoeostasis through interaction with effector proteins. As the bulk of cellular sterols are segregated from the sensory machinery that controls homoeostatic responses, an important regulatory step involves sterol transport or signalling between membrane compartments. Evidence for rapid, energy-independent transport between organelles has implicated transport proteins, such as the eukaryotic family of OSBP (oxysterol-binding protein)/ORPs (OSBP-related proteins). Since the founding member of this family was identified more than 25 years ago, accumulated evidence has implicated OSBP/ORPs in sterol signalling and/or sterol transport functions. However, recent evidence of sterol transfer activity by OSBP/ORPs suggests that other seemingly disparate functions could be the result of alterations in membrane sterol distribution or ancillary to this primary activity.

Rice plants response to the disruption of OsCSLD4 gene

Plant cell wall is a complex polysaccharide network and performs important developmental and physiological functions far beyond supplying the physical constrains. Plant cells have the ability to react to cell wall defects as exhibited by changes in gene expression, accumulation of ectopic lignin, stress responses, and growth arrest. It is a major challenge to understand how plants sense and response to wall integrity since very little is known about the signaling involved in the responses. Cellulose synthase-like D (CSLD) proteins mediating the biosynthesis of a wall polysaccharide polymer make up a common subfamily to all plants. Recently, we have reported the functional characterization of CSLD4 in rice. Mutation in OsCSLD4 shows morphological alterations and pleiotropic effects on wall compositions and structure. Our study demonstrates that OsCSLD4 plays critical roles in cell wall formation and plant growth. Here we show the subtle wall alterations through separating the culm residues into five fractions. Quantitative RT-PCR analysis further revealed that the expression of various genes involved in xylan synthesis and cell-cycle regulation was altered in mutant plants, as the responses to OsCSLD4 disruption. Therefore, plants may have a fine sensory machinery to react to wall defects and modulate growth for adapting to the changes.

Modular Design of Immunological Synapses and Kinapses

The concept of an immunological synapse goes back to the early 1980s with the discovery of the relationship between T-cell antigen receptor mediated Ca(2+) signaling, adhesion, and directed secretion. However, this concept did not gain traction until images were published starting in 1998 that revealed a specific molecular pattern in the interface between T cells and model antigen-presenting cells or supported planar bilayers. The dominant pattern, a ring of adhesion molecules surrounding a central cluster of antigen receptors, was observed in both model systems. Analysis of the origins of this pattern over the past 10 years has presented a solution for a difficult problem in lymphocyte biology--how a highly motile cell can suddenly stop when it encounters a signal delivered by just a few antigenic ligands on the surface of another cell without disabling the sensory machinery of the motile cell. The T lymphocyte actively assembles the immunological synapse pattern following a modular design with roots in actin-myosin-based motility.

Progress in the detection of costs of phenotypic plasticity in plants

Progress in the detection of costs of phenotypic plasticity in plants

Expression of mammalian GPCRs in C. elegans generates novel behavioural responses to human ligands.

BackgroundG-protein-coupled receptors (GPCRs) play a crucial role in many biological processes and represent a major class of drug targets. However, purification of GPCRs for biochemical study is difficult and current methods of studying receptor-ligand interactions involve in vitro systems. Caenorhabditis elegans is a soil-dwelling, bacteria-feeding nematode that uses GPCRs expressed in chemosensory neurons to detect bacteria and environmental compounds, making this an ideal system for studying in vivo GPCR-ligand interactions. We sought to test this by functionally expressing two medically important mammalian GPCRs, somatostatin receptor 2 (Sstr2) and chemokine receptor 5 (CCR5) in the gustatory neurons of C. elegans.ResultsExpression of Sstr2 and CCR5 in gustatory neurons allow C. elegans to specifically detect and respond to somatostatin and MIP-1α respectively in a robust avoidance assay. We demonstrate that mammalian heterologous GPCRs can signal via different endogenous Gα subunits in C. elegans, depending on which cells it is expressed in. Furthermore, pre-exposure of GPCR transgenic animals to its ligand leads to receptor desensitisation and behavioural adaptation to subsequent ligand exposure, providing further evidence of integration of the mammalian GPCRs into the C. elegans sensory signalling machinery. In structure-function studies using a panel of somatostatin-14 analogues, we identified key residues involved in the interaction of somatostatin-14 with Sstr2.ConclusionOur results illustrate a remarkable evolutionary plasticity in interactions between mammalian GPCRs and C. elegans signalling machinery, spanning 800 million years of evolution. This in vivo system, which imparts novel avoidance behaviour on C. elegans, thus provides a simple means of studying and screening interaction of GPCRs with extracellular agonists, antagonists and intracellular binding partners.

TheC. eleganshomologs of nephrocystin-1 and nephrocystin-4 are cilia transition zone proteins involved in chemosensory perception

Nephronophthisis (NPH) is a cystic kidney disorder that causes end-stage renal failure in children. Five nephrocystin (nephrocystin-1 to nephrocystin-5) genes, whose function is disrupted in NPH patients, have been identified and data indicate they form a complex at cell junctions and focal adhesions. More recently, the nephrocystin proteins have also been identified in cilia, as have multiple other cystic kidney disease related proteins. Significant insights into this cilia and cystic kidney disease connection have come from analyses in simpler eukaryotic organisms such as Caenorhabditis elegans. In this regard, we became interested in the C. elegans homologs of nephrocystin-1 (nph-1) and nephrocystin-4 (nph-4) from a database screen to identify genes coordinately regulated by the ciliogenic transcription factor DAF-19. Here we show that expression of nph-1 and nph-4 is DAF-19 dependent, that their expression is restricted to ciliated sensory neurons, and that both NPH-1 and NPH-4 concentrate at the transition zones at the base of the cilia, but are not found in the cilium axoneme. In addition, NPH-4 is required for the localization of NPH-1 to this domain. Interestingly, nph-1 or nph-4 mutants have no obvious cilia assembly defects; however, they do have abnormalities in cilia-mediated sensory functions as evidenced by abnormal chemotaxis and lifespan regulation. Our data suggest that rather than having a ciliogenic role, the NPH proteins play an important function as part of the sensory or signaling machinery of this organelle. These findings suggest that the defects in human NPH patients may not be the result of aberrant ciliogenesis but abnormal cilia-sensory functions.

Cell wall-cytoplasm signalling

The cell wall is no longer considered an inert and silent structure on the outside of the cell but instead, seems to be involved in an extensive cross-talk with the cytoplasm. Turgor, osmosensing, mechanical stress and other strains - all are mediated through the wall. The walled cell senses these signals through integral plasma membrane proteins whose extracytoplasmic domains are extended to the wall and intracytoplasmic domains are coupled with the components of cytoplasmic signal pathways. With its dynamic interactions the cell wall is comparable with the extracellular matrix of animal cells. Only a small part of the sensory machinery has been revealed in both plant and fungal cells.

Sensing the Direction of Stress

Many cells will respond to a tug or a nudge by activating appropriate signaling pathways that ultimately regulate gene expression. But just how cells sense such mechanical strain remains poorly understood. Kumar et al. report observations that begin to reveal previously unrecognized complexity in the sensory machinery. The authors studied responses of diaphragm muscle from mice in vitro. The diaphragm has the unusual property of experiencing mechanical load not only axially, that is, in the direction along the length of the muscle fibers, but also transversely, across the fibers. Both axial and transverse stretching activate the mitogen-activated protein kinases (MAPKs) ERK1 and ERK2, which in turn are linked to activation of p90 RSK (ribosomal protein S6 kinase) and activation of the AP1 transcription factor complex. However, transverse stretching was more effective in activating such signals than was axial stretching. The cell's capacity to detect the direction of mechanical stress was revealed in experiments with pharmacological inhibitors that interfered with specific signaling pathways. Axial stretching activated ERK1 and ERK2 by a mechanism that required signaling through phosphoinositide 3-kinase, intracellular calcium release, protein kinase C, and the MAPK kinases MEK1 or MEK2. In contrast, transverse stretching of the muscle cells activated ERKs 1and 2 in a manner that required cAMP (adenosine 3′-5′ monophosphate)-dependent protein kinase. The authors conclude that diaphragm muscles appear to have two distinct pathways leading to ERK activation and altered gene expression with each responding to mechanical stress in a particular direction. A. Kumar, I. Chaudhry, M. B. Reid, A. M. Boriek, Distinct signaling pathways are activated in response to mechanical stress applied axially and transversely to skeletal muscle fibers. J. Biol. Chem. 277 , 46493-46503 (2002). [Abstract] [Full Text]

Cross-talk between cellular stress, cell cycle and anticancer agents: mechanistic aspects.

Environmental conditions such as temperature, radiation, hypoxia, nutrients and drugs stimulate the adaptive sensory and signaling machinery of the cell. This stress response may influence cell cycle regulation, cellular differentiation, oncogenic transforma-tion, cell survival and apoptosis. The impact of the cytoprotective reprogramming in cancer pharmacology is presented by the recent extensive literature regarding the interplay between stress tolerance and anticancer drug effectiveness and resistance, relying on the dominating intrinsic pathways, which are simultaneously activated and regulate the death process either positively or negatively. This review presents the data that argue for the emergence of either common or specific mechanisms depending on the type, duration and severity of stress in all eukaryotic organisms from yeast to mammals. The understanding of the complexity and the balance between noxious and protective signal transduction pathways would contribute to a more explicit evaluation of the current therapeutic regiments and to the development of new leads targeting malignancy.

Costs and limits of phenotypic plasticity

The costs and limits of phenotypic plasticity are thought to have important ecological and evolutionary consequences, yet they are not as well understood as the benefits of plasticity. At least nine ideas exist regarding how plasticity may be costly or limited, but these have rarely been discussed together. The most commonly discussed cost is that of maintaining the sensory and regulatory machinery needed for plasticity, which may require energy and material expenses. A frequently considered limit to the benefit of plasticity is that the environmental cues guiding plastic development can be unreliable. Such costs and limits have recently been included in theoretical models and, perhaps more importantly, relevant empirical studies now have emerged. Despite the current interest in costs and limits of plasticity, several lines of reasoning suggest that they might be difficult to demonstrate.

Chemical Structure-Odor Correlation in a Series of Synthetic n-Nonen-1-ols

In order to elucidate chemical structure-odor correlation in the all isomers of n-nonen-1- ols, an entire series of these alcohols were synthesized stereo-selectively in high purity. For unequivocal syntheses of them, geometrically selective hydrogenation of the respective acetylenic compound was adopted. The synthesized alcohols were converted to their 3,5-dinitrobenzoate derivatives with 3,5-dinitrobenzoyl chloride, and then purified by repeated recrystallization. Chemical structure-odor correlations in all the isomers of n-nonen-1-ols were elucidated by introducing a novel method to evaluate odor characteristics and by treating the obtained data statistically with the principal component analysis method (Cramer et al., 1988). The odor profiles of the tested compounds were attributable largely to the positions of the carbon- double bond. The geometries of compounds had only a little effect. With the principal component analysis, the odor profiles of the series of compounds were successfully integrated into the first and the second principal components. The first component (PC-1) consisted of combined characteristics of fruity, fresh, sweet, herbal and oily-fatty, in which herbal and oily-fatty were conversely correlated each other to the position of double-bond of the tested compounds. Of these, only (6Z)-nonen-1-ol deviated markedly from the correlation, indicative of some special interaction between the spatial structure of this compound and the sensory machinery of human.

Differential surface models for tactile perception of shape and online tracking of features

The online kinematic problem for gliding or rolling on an unknown surface is addressed, treating it as a simple two-rigid-body problem. A planar rigid-body end effector is considered that maintains contact with a rigid body of unknown shape by gliding or rolling on it. The smooth surface of the end effector is assumed to be known implicitly or parametrically in its own coordinate system. The authors present the main results both in equation form and diagrammatically. The figure given implies that if the parameters of the robot are known as well as its state, the forces of contact can be computed. However, due to the extensive amount of data required for this condition to be met, the required sensory and computational machinery may be exorbitant. Moreover, the presence of noise and the cost of removing it sufficiently make this approach impractical at present. >

Kinetics of movement of normal and mutant nematodes

The nematode,Caenorhabditis elegans, is strongly attracted towards secretions ofEscherichia coli. The movement of a population of nematodes from the center of an agar plate through a gradient of these secretions towards bacteria at the circumference can be represented by a series of first-order rate processes. Normal and mutant strains of various kinds demonstrate marked differences in their rates of movement. This method of kinetic analysis appears to have a useful potential in the characterization of mutants in nerve and muscle as to whether sensory or locomotive machinery is affected and in the isolation of new mutants of these types.

The Physiology of Taste.

The word taste means many things to many men as, indeed, most words do and all words may. As a strict physiological term the function of taste from the buds on the tongue includes the sensation of salt, bitter, acid, or sour. The bulk of what we refer to as taste in ordinary parlance is the olfactory element. Smell can be highly developed. It is reputed that the sensory machinery of professional perfume sniffers is able to identify hundreds, perhaps even thousands, of different odors. So keen is their nose that they are said to be able to identify a few scents in concentrations of only a few molecules. In its broader use the word taste comes to imply all the paraphernalia of almost automatic discrimination and judgment which enable the devotee of the fine arts of literature, painting, or music to separate and skim off, as it were, for