Ultrastructure of the dendritic outer segments of sensory cells in poreless (‘no-pore’) sensilla of insects

Summary Poreless sensilla with inflexible sockets in insects presumably house hygro- and thermoreceptors (type-1, type-2 receptors). The dendritic outer segments of these receptor cells were studied mainly in cryofixed antennae of two species of moth (Antheraea pernyi, A. polyphemus) and one beetle (Aleochara curtula). As a rule two type-1 receptor cells are present. Their dendritic outer segments do not branch. They project into the distal cuticular parts of the sensillum and are in close contact with its four-layered wall. The segments differ in shape and microtubule density. As well, in A. curtula, the microtubules are interconnected by electron-dense material for some distance, thus forming a tubular body-like structure of 1.3 m length. The dendritic outer segment of the single type-2 receptor cell is branched and lamellated. Its lamellae are connected by structures similar to septate junctions, which occupy about 70% of the total surface of the lamellated portion of the dendrite. In tangential sections, the septa appear as parallel strands approximately perpendicular to the long axis of the dendritic segment. The structure of type-1 receptors is discussed with regard to the hypothesis for a mechano-electrical transduction. The possible functions of lamellation and junctional connections in type-2 receptors are discussed.Supported by the Deutsche Forschungsgemeinschaft (SFB 4/G1)     

Effects of whole body vibration on outer hair cells’ hearing response to distortion product otoacoustic emissions

Whole body vibration (WBV) is one of the most vexing problems in industries. There is a debate about the effect of WBV exposure on hearing system as vibration-induced hearing loss. The purpose of this study was to investigate outer hair cells' (OHCs') hearing response hearing response to distortion product otoacoustic emissions (DPOAEs) in rabbits exposed to WBV. It was hypothesized that the DPOAE response amplitudes (A(dp)) in rabbits exposed to WBV would be lower than those in control rabbits not exposed to WBV. New Zealand white (NZW) rabbits as vibration group (n = 6, exposed to WBV in the z-axis at 4-8 Hz and 1.0 ms(-2) root mean square for 8 h per day during five consecutive days) and NZW rabbits as control group (n = 6, not exposed to any WBV) were participated. A(dp) and noise floor levels (L(nf)) were examined on three occasions: day 0 (i.e., baseline), day 8 (i.e., immediately 1 h after exposure), and day 11 (i.e., 72 h following exposure) with f(2) frequencies ranging from 500 to 10,000 Hz and primaries L(1) and L(2) levels of 65 and 55 dB sound pressure level, respectively. Main effects were statistically found to be significant for group, time, and frequency (p < 0.05). DPOAE amplitudes were significantly larger for rabbits exposed to WBV, larger on day 8 and larger for mid to high f(2) frequencies (at and above 5,888.50 Hz). Main effects were not statistically found to be significant for ear (p > 0.05). Also, four statistically significant interactions including time by ear, time by frequency, group by frequency, and group by time were detected (p < 0.05). Contrary to the main hypothesis, DPOAE amplitudes were significantly larger for rabbits exposed to WBV. WBV exposure significantly led to enhanced mean A(dp) at mid to high frequencies rather than at low ones.     

‘Disk shedding’ in the cone outer segments of the teleost,Poecilia reticulata P.

Summary Electron microscopical observations show that the cones in the retina of the diurnal Poecilia reticulata shed their membranous outer segment disks. This occurs at the side of the disk which is open to the extracellular space. Shedding is observed in single and twin cones and occurs at any level of the outer segment. The disks are not discarded in packages or as single disks, but are shed in small vesicular portions. This mode of disk shedding may explain why in cone outer segments radioactively labelled replacement protein is diffusely distributed.The authors wish to thank Dr. C. Wise of this Department for helpful discussions     

Have we found the tip link,transduction channel,and gating spring of the hair cell?

Recent reports have offered candidates for key components of the apparatus used for mechanotransduction in hair cells. TRPA1 and cadherin 23 have been proposed to be the transduction channel and component of the tip link, respectively; moreover, ankyrin repeats in TRPA1 have been proposed to be the gating spring. Although these are excellent candidates for the three components, definitive experiments supporting each identification have yet to be performed.     

Generation of somatic electromechanical force by outer hair cells may be influenced by prestin–CASK interaction at the basal junction with the Deiter’s cell

The motor protein, prestin, situated in the basolateral plasma membrane of cochlear outer hair cells (OHCs), underlies the generation of somatic, voltage-driven mechanical force, the basis for the exquisite sensitivity, frequency selectivity and dynamic range of mammalian hearing. The molecular and structural basis of the ontogenetic development of this electromechanical force has remained elusive. The present study demonstrates that this force is significantly reduced when the immature subcellular distribution of prestin found along the entire plasma membrane persists into maturity, as has been described in previous studies under hypothyroidism. This observation suggests that cochlear amplification is critically dependent on the surface expression and distribution of prestin. Searching for proteins involved in organizing the subcellular localization of prestin to the basolateral plasma membrane, we identified cochlear expression of a novel truncated prestin splice isoform named prestin 9b (Slc26A5d) that contains a putative PDZ domain-binding motif. Using prestin 9b as the bait in a yeast two-hybrid assay, we identified a calcium/calmodulin-dependent serine protein kinase (CASK) as an interaction partner of prestin. Co-immunoprecipitation assays showed that CASK and prestin 9b can interact with full-length prestin. CASK was co-localized with prestin in a membrane domain where prestin-expressing OHC membrane abuts prestin-free OHC membrane, but was absent from this area for thyroid hormone deficiency. These findings suggest that CASK and the truncated prestin splice isoform contribute to confinement of prestin to the basolateral region of the plasma membrane. By means of such an interaction, the basal junction region between the OHC and its Deiter’s cell may contribute to efficient generation of somatic electromechanical force.     

Thyroid hormone receptor α1 is a critical regulator for the expression of ion channels during final differentiation of outer hair cells

Cochlear outer hair cells (OHCs) terminally differentiate prior to the onset of hearing. During this time period, thyroid hormone (TH) dramatically influences inner ear development. It has been shown recently that TH enhances the expression of the motor protein prestin via liganded TH receptor β (TRβ) while in contrast the expression of the potassium channel KCNQ4 is repressed by unliganded TRα1. These different mechanisms of TH regulation by TRα1 or TRβ prompted us to analyse other ion channels that are required for the final differentiation of OHCs. We analysed the onset of expression of the Ca²⁺ channel Ca_V1.3, and the K⁺ channels SK2 and BK and correlated the results with the regulation via TRα1 or TRβ. The data support the hypothesis that proteins expressed in rodents prior to or briefly after birth like Ca_V1.3 and prestin are either independent of TH (e.g. Ca_V1.3) or enhanced through TRβ (e.g. prestin). In contrast, proteins expressed in rodents later than P6 like KCNQ4 (∼P6), SK2 (∼P9) and BK (∼P11) are repressed through TRα1. We hypothesise that the precise regulation of expression of the latter genes requires a critical local TH level to overcome the TRα1 repression. Harald Winter and Claudia Braig contributed equally to this work.     

Contribution of Müller cells toward the regulation of photoreceptor outer segment assembly

The assembly of photoreceptor outer segments into stacked discs is a complicated process, the precise regulation of which remains a mystery. It is known that the integrity of the outer segment is heavily dependent upon surrounding cell types including the retinal pigment epithelium and Müller cells; however the role played by Müller cells within this photoreceptor-specific process has not been fully explored. Using an RPE-deprived but otherwise intact Xenopus laevis eye rudiment preparation, we reveal that Müller cell involvement in outer segment assembly is dependent upon the stimulus provided to the retina. Pigment epithelium-derived factor is able to support proper membrane folding after inhibition of Müller cell metabolism by alpha-aminoadipic acid, while isopropyl beta-D-thiogalactoside, a permissive glycan, requires intact Müller cell function. These results demonstrate that both intrinsic and extrinsic redundant mechanisms exist to support the ability of photoreceptors to properly assemble their outer segments. Our study further suggests that the receptor for pigment epithelium-derived factor resides in photoreceptors themselves while that for permissive glycans is likely localized to Müller cells, which in turn communicate with photoreceptors to promote proper membrane assembly.     

Kinetics of degradation of ‘short-’ and ‘long-lived’ proteins in cultured mammalian cells

Two distinct classes of protein referred to as short- and long-lived (Poole and Wibo, 1973) were found in pulse-chased HeLa S-3 and BHK 21/C13 cells. From experiments with pulse times ranging from 1 min to 20 h, a clear inverse correlation emerged between the pulse length and the percentage of protein which was hydrolysed intracellularly in the first h of chase. Using a 5 min pulse labelling with ³H-leucine, cells were either harvested immediately or after a 2 h chase. Approximately 35% of the label incorporated by cells was lost in a 2h chase; however, electrophoretic separation of cytosol and residual cytoplasmic fractions revealed no significant alteration in their protein profiles. The technique of selectively labelling ‘short’ and ‘long-lived’ proteins, which implies qualitative differences between them, is more readily interpreted as an artificial polarisation of a declining statistical probability curve of proteolysis with time which is similar for all nascent proteins.     

Characterization and resuscitation of ‘non-culturable’ cells of Legionella pneumophila

Background

Legionella pneumophila is a waterborne pathogen responsible for Legionnaires’ disease, an infection which can lead to potentially fatal pneumonia. After disinfection, L. pneumophila has been detected, like many other bacteria, in a “viable but non culturable” state (VBNC). The physiological significance of the VBNC state is unclear and controversial: it could be an adaptive response favoring long-term survival; or the consequence of cellular deterioration which, despite maintenance of certain features of viable cells, leads to death; or an injured state leading to an artificial loss of culturability during the plating procedure. VBNC cells have been found to be resuscitated by contact with amoebae.

Results

We used quantitative microscopic analysis, to investigate this “resuscitation” phenomenon in L. pneumophila in a model involving amending solid plating media with ROS scavengers (pyruvate or glutamate), and co-culture with amoebae. Our results suggest that the restoration observed in the presence of pyruvate and glutamate may be mostly due to the capacity of these molecules to help the injured cells to recover after a stress. We report evidence that this extracellular signal leads to a transition from a not-culturable form to a culturable form of L. pneumophila, providing a technique for recovering virulent and previously uncultivated forms of L. pneumophila.

Conclusion

These new media could be used to reduce the risk of underestimation of counts of virulent of L. pneumophila cells in environmental samples.     

Jasmonates trigger prey-induced formation of ‘outer stomach’ in carnivorous sundew plants

It has been widely accepted that the growth-related phytohormone auxin is the endogenous signal that initiates bending movements of plant organs. In 1875, Charles Darwin described how the bending movement of leaves in carnivorous sundew species formed an ‘outer stomach’ that allowed the plants to enclose and digest captured insect prey. About 100 years later, auxin was suggested to be the factor responsible for this movement. We report that prey capture induces both leaf bending and the accumulation of defence-related jasmonate phytohormones. In Drosera capensis fed with fruitflies, within 3 h after prey capture and simultaneous with leaf movement, we detected an increase in jasmonic acid and its isoleucine conjugate. This accumulation was spatially restricted to the bending segment of the leaves. The application of jasmonates alone was sufficient to trigger leaf bending. Only living fruitflies or the body fluids of crushed fruitflies induced leaf curvature; neither dead flies nor mechanical treatment had any effect. Our findings strongly suggest that the formation of the ‘outer stomach’ in Drosera is a chemonastic movement that is triggered by accumulation of endogenous jasmonates. These results suggest that in carnivorous sundew plants the jasmonate cascade might have been adapted to facilitate carnivory rather than to defend against herbivores.     

Entangled Matters—Alzheimer’s,Interiority, and the ‘Unflattening’ of the World

When, in the 1980s, Alzheimer's disease became a disease of major public concern, 'personhood' also became an important, related topic of discussion. Those in caring professions (psychology, social work, etc.) and caregiver groups advocated for the 'person within' who was getting lost in a forgetful body and in a reductionist biomedical system. This essay aims to critically approach the dualism of this kind of argument by focusing on the moral positioning of claims such as personhood or biomedical reductionism.     

How can we meet ‘the demands of the day’? Producing an affective,reflexive, interpretive,public sociology of ‘race’

This article argues for a public sociology of ‘race’ that can respond to Weber's injunction that sociology should ‘meet the demands of the day’. While the author's version of these demands – for a society of autonomous individuals and groups, living as equals – is utopian, the main argument offered here is that a sociology of ‘race’ should be a modified version of Burawoy's ‘public sociology’. Adopting Bauman's notion of a sociology of interpreters, a further suggestion is that this type of sociology needs to be reflexive and affective. Based on an analysis of his own sociological education in the late 1960s, his participation in social and political movements in which ‘race’ was key, and with brief reference to the sociology of ‘race’, the author argues that the emotions that circulated in each arena need to be examined, acknowledged and incorporated if theoretical and practical progress is to be made.     

Structural and Narrative Reconstruction of Rural Residents’ Representations of ‘Nature’, ‘Wildlife’, and ‘Landscape’

The objective of this paper is the structural and narrative reconstruction of representations of ‘nature’, ‘wildlife’ and ‘landscape’, held by rural residents of the Dadia Forest Reserve. Data collection involved in-depth interviews. Employing a social representations’ approach, we recovered representational elements that are expected in the case of rural belief systems, such as negative dispositions towards wolves and foxes, as well as elements of an urban adherence, such as nature’s independence. Representational elements refer to visual aspects of the countryside, which seem compatible with the figurative nucleus of the rural idyll. Concerning ‘wildlife’, residents focused on vultures, which comprise the main tourist attraction of the reserve. Scientific knowledge adds to the complexity of the narrative schema, which corresponds to the representation of ‘wildlife’. Interviewees perceived the rural landscape as an interface between the natural and the human-conditioned environment. Our study shows that interviewees make no reference to environmental conservation or quality of life issues, as it could be expected according to relatively wide definitions of the term ‘environmentalism’. Environmental messages reinforced by ecotourism development seem to be recalled primarily in terms of their compatibility with the perceived economic benefit of local people. Despite ecotourism development, representational elements that diverge from a tourist version of ‘nature’, ‘wildlife’ and ‘landscape’ were not pronounced within rural belief-systems. Further interventions within the study area are needed, in order to address a variety of topics under the environmental conservation discourse and raise the environmental awareness of rural residents.     

The sulfate-reducing bacterial community of sulfide-rich water of the Ust’-Kachka resort spring, Perm Krai, Russia

Microbiological investigation of the highly mineralized, sulfide-rich cold spring of the Ust??-Kachka resort was carried out. The total number and biomass of microbial cells were 50 × 10³ cell/mL and 15 ??g/L, respectively. While the total microbial number was low, the sulfate reduction rate determined by the radioisotope method was relatively high (0.575 mg S L^?1 day^?1). An enrichment culture was obtained on Widdel medium. According to the results of cloning the 16S rRNA gene fragments with subsequent restriction analysis, the dominant organisms were group 6 sulfate-reducing bacteria (Desulfovibrio-Desulfomicrobium) and the microorganism exhibiting 99% similarity to the anaerobic haloalkaliphilic bacterium Halanaerobium hydrogeniformans.     

Spectacles of migrant ‘illegality’: the scene of exclusion,the obscene of inclusion

Abstract

Border policing and immigration law enforcement produce a spectacle that enacts a scene of ‘exclusion’. Such spectacles render migrant ‘illegality’ visible. Thus, these material practices help to generate a constellation of images and discursive formations, which repetitively supply migrant ‘illegality’ with the semblance of an objective fact. Yet, the more these spectacles fuel anti-immigrant controversy, the more the veritable inclusion of the migrants targeted for exclusion proceeds apace. Their ‘inclusion’ is finally devoted to the subordination of their labour, which is best accomplished only insofar as their incorporation is persistently beleaguered with exclusionary campaigns that ensure that this inclusion is itself a form of subjugation. At stake, then, is a larger sociopolitical (and legal) process of inclusion through exclusion. This we may comprehend as the obscene of inclusion. The castigation of ‘illegals’ thereby supplies the rationale for essentializing citizenship inequalities as categorical differences that then may be racialized.     

The ‘shock period’: dynamics of phytoplankton during the spring–summer transition of a stratifying English lake

The spring to summer transition in a productive English lake is considered with respect to phytoplankton and its environmental conditions. Salient environmental changes include the onset of temperature/density stratification that is usually accompanied by a clear-water phase associated with a maximum of grazing Daphnia and a minimum of phytoplankton in the 0â€5 m zone. Below this zone, as thermal stratification progresses, a deep maximum of phytoplankton can develop under strong thermal/density gradients and enhanced light penetration. Examples are resolved by estimations of chlorophyll-a , beam attenuance in situ and cell counts. Attributed origins are by sedimentation of diatoms, migration of flagellates, and depth-adjusted buoyancy of a gas-vacuolate cyanophyte. The transition period involves a decline of spring-associated diatom populations and a rise of summer-associated species. The generally low algal abundance within the transition phase has at least four origins †prior nutrient (Si) depletion, sedimentation, grazing, and low inoculum levels of successor species. It can be augmented by the re-growth of species abundant in spring, by early extensions of normally summer species, by seasonally characteristic colonial chrysophytes, and by other phytoflagellates of small size that are seasonally less specific (opportunistic) and probably critical for Daphnia grazing with consequent generation of the clear-water phase.