Visual accommodation in vertebrates: mechanisms, physiological response and stimuli

The mechanism and stimulation of the accommodative reflex in vertebrate eyes are reviewed. Except for lampreys, accommodation is brought about by intraocular muscles that mediate either a displacement or deformation of the lens, a change of the corneal radius of curvature or a combination of these mechanisms. Elasmobranchs have little accommodation and are emmetropic in water rather than hyperopic as commonly stated. Accommodation in teleosts and amphibians is well understood and achieved by lens displacement. The accommodative mechanism of amniotes is of considerable diversity and reflects different lifestyles rather than phylogenetical relationships. In all amniotes, the ciliary muscle never has a direct impact on the lens. It relaxes the tension applied to the lens by zonular fibers and/or ligaments. In birds and reptiles the ciliary muscle is usually split into two parts, of which the anterior portion changes the corneal radius of curvature. The deformation of the lens is generally achieved either by its own elasticity (humans, probably other mammals and sauropsids) or by the force of circular muscle fibers in the iris (reptiles, birds, aquatic mammals). In the second part of the paper, some of the current hypotheses about the accommodative stimulus are reviewed together with physiological response characteristics.     

Bioenergetics of the lower vertebrates. Molecular mechanisms of adaptations to anoxia and hypoxia

In this review, causes of tremendous differences in respiration and oxidative metabolism between the homoiothermal and poikilothermal vertebrates are discussed. Tissues of the latter contain no lower, and sometimes even higher amount of mitochondria with the powerful potential of oxidative enzymes, as compared with the homoiothermal vertebrates; only 3–4% of this potential are realized due to a low rate of oxygen transport because of peculiarities of the cardiovascular system of the lower vertebrates. Limitation of the ATP synthesis provided a specific structure of plasma membranes with the much lower amount of channels for the passive ion leak as compared with the mammalian plasma membranes. Examples are presented of the homoiothermal animal cells (the frog olfactory receptor cell) that contact environment without participation of the blood circulation system and have the energy metabolism level comparable with that of mammalian cells. Examples of energetic aromorphosis are tunas with heat exchangers in several organs and with a powerful system of oxygen delivery to cells; owing to this, intensity of their oxidative metabolism could reach that of the higher terrestrial vertebrates. The closing part of this paper describes the molecular mechanisms that allow some representatives of reptiles, amphibians, and fish to survive long periods of hypoxia and anoxia.     

Differential dynamic properties of scleroderma fibroblasts in response to perturbation of environmental stimuli

Diseases are believed to arise from dysregulation of biological systems (pathways) perturbed by environmental triggers. Biological systems as a whole are not just the sum of their components, rather ever-changing, complex and dynamic systems over time in response to internal and external perturbation. In the past, biologists have mainly focused on studying either functions of isolated genes or steady-states of small biological pathways. However, it is systems dynamics that play an essential role in giving rise to cellular function/dysfunction which cause diseases, such as growth, differentiation, division and apoptosis. Biological phenomena of the entire organism are not only determined by steady-state characteristics of the biological systems, but also by intrinsic dynamic properties of biological systems, including stability, transient-response, and controllability, which determine how the systems maintain their functions and performance under a broad range of random internal and external perturbations. As a proof of principle, we examine signal transduction pathways and genetic regulatory pathways as biological systems. We employ widely used state-space equations in systems science to model biological systems, and use expectation-maximization (EM) algorithms and Kalman filter to estimate the parameters in the models. We apply the developed state-space models to human fibroblasts obtained from the autoimmune fibrosing disease, scleroderma, and then perform dynamic analysis of partial TGF-beta pathway in both normal and scleroderma fibroblasts stimulated by silica. We find that TGF-beta pathway under perturbation of silica shows significant differences in dynamic properties between normal and scleroderma fibroblasts. Our findings may open a new avenue in exploring the functions of cells and mechanism operative in disease development.     

Morphological and biochemical adaptations to feeding in some herbivorous gastropods

Feeding range and modes as well as morphological and biochemical adaptations to feeding are analyzed in herbivorous mollusks. The content of hemoglobin in radular tissues and weight properties of the radula are evaluated for different modes of feeding.Translated from Izvestiya Akademii Nauk, Seriya Biologicheskaya, No. 1, 2005, pp. 69–77.Original Russian Text Copyright © 2005 by Alyakrinskaya.     

Importance of lineage-specific expansion of plant tandem duplicates in the adaptive response to environmental stimuli

Plants have substantially higher gene duplication rates compared with most other eukaryotes. These plant gene duplicates are mostly derived from whole genome and/or tandem duplications. Earlier studies have shown that a large number of duplicate genes are retained over a long evolutionary time, and there is a clear functional bias in retention. However, the influence of duplication mechanism, particularly tandem duplication, on duplicate retention has not been thoroughly investigated. We have defined orthologous groups (OGs) between Arabidopsis (Arabidopsis thaliana) and three other land plants to examine the functional bias of retained duplicate genes during vascular plant evolution. Based on analysis of Gene Ontology categories, it is clear that genes in OGs that expanded via tandem duplication tend to be involved in responses to environmental stimuli, while those that expanded via nontandem mechanisms tend to have intracellular regulatory roles. Using Arabidopsis stress expression data, we further demonstrated that tandem duplicates in expanded OGs are significantly enriched in genes that are up-regulated by biotic stress conditions. In addition, tandem duplication of genes in an OG tends to be highly asymmetric. That is, expansion of OGs with tandem genes in one organismal lineage tends to be coupled with losses in the other. This is consistent with the notion that these tandem genes have experienced lineage-specific selection. In contrast, OGs with genes duplicated via nontandem mechanisms tend to experience convergent expansion, in which similar numbers of genes are gained in parallel. Our study demonstrates that the expansion of gene families and the retention of duplicates in plants exhibit substantial functional biases that are strongly influenced by the mechanism of duplication. In particular, genes involved in stress responses have an elevated probability of retention in a single-lineage fashion following tandem duplication, suggesting that these tandem duplicates are likely important for adaptive evolution to rapidly changing environments.     

Morphological adaptations of the digestive tract of tropical cyprinids and cichlids to diet

Eight cyprinids with four different feeding habits fall into two distinct groups according to morphological adaptations of the intestine: (i) carnivorous and omnivorous cyprinids with large gut diameter and large mucosal surface which decreases from the foregut to the hindgut; (ii) benthivorous and phytoplanktivorous cyprinids with small gut diameter and small mucosal surface which is more or less uniformly built along the intestine, although relative gut length may vary considerably (1.45–6.10). Although the intestine of phytoplanktivorous cyprinids is extremely elongated, it appears less adapted for processing a refractory diet than that of cichlids with similar feeding habits.     

Oxidative stress induces autophagy in response to multiple noxious stimuli in retinal ganglion cells

Retinal ganglion cells (RGCs) are the only afferent neurons that can transmit visual information to the brain. The death of RGCs occurs in the early stages of glaucoma, diabetic retinopathy, and many other retinal diseases. Autophagy is a highly conserved lysosomal pathway, which is crucial for maintaining cellular homeostasis and cell survival under stressful conditions. Research has established that autophagy exists in RGCs after increasing intraocular pressure (IOP), retinal ischemia, optic nerve transection (ONT), axotomy, or optic nerve crush. However, the mechanism responsible for defining how autophagy is induced in RGCs has not been elucidated. Accumulating data has pointed to an essential role of reactive oxygen species (ROS) in the activation of autophagy. RGCs have long axons with comparatively high densities of mitochondria. This makes them more sensitive to energy deficiency and vulnerable to oxidative stress. In this review, we explore the role of oxidative stress in the activation of autophagy in RGCs, and discuss the possible mechanisms that are involved in this process. We aim to provide a more theoretical basis of oxidative stress-induced autophagy, and provide innovative targets for therapeutic intervention in retinopathy.     

The evolution of the terrestrial vertebrates: environmental and physiological considerations

Physiological evidence has long been used to suggest that the gnathostomous vertebrates (those possessing jaws) were primitively fresh water. The same was also the case for the Osteichthyes (bony fish) and the Tetrapoda (Amphibia, Reptilia, Aves, Mammalia). However, the geological evidence favours a marine origin for the vertebrates as a whole, and, for the gnathostomes and the osteichthyans in particular. Some of the earliest amphibian remains may be associated with tidally influenced sediments. Furthermore, during the early part of the Devonian, fresh water chemistry may well have been different from that of today, lessening the divide between marine and non-marine environments. Urea formation via the ornithine cycle, and urea retention in the body fluids, are useful adaptations for terrestrial life. They prevent excessive water loss associated with the elimination of nitrogenous waste. These abilities may have been primitive for the gnathostomes, and were developed in the marine environment to reduce osmotic dehydration. In the aqueous medium, gaseous exchange is effected by the gills. These organs are, on the whole, useless in air. For vertebrates, air-breathing is effected by an inflatable sac, with moist linings, and an internal location. Some form of air-breathing sac was primitive for the osteichthyans, and may have been primitive for the gnathostomes. Again, this adaptation for terrestrial life developed in response to conditions experienced in the marine, aquatic environment. A new model of tetrapod evolution is proposed in the light of the basic marine origin and character of the ancestors of the tetrapods.     

Morphological and behavioral antipredatory adaptations of decapod zoeae

Summary Zoeae of some species of estuarine decapods are retained in the estuary throughout development while others are exported into nearshore coastal waters. The horizontal migrations of decapod zoeae to coastal waters may have evolved to reduce the probability of encountering planktivorous fishes which are most abundant in the estuary. If so, then the morphological vulnerability of zoeae to fish predation should be inversely related to the number of predators occurring where they develop. Six species of estuarine decapod zoeae were offered to Menidia menidia and Fundulus heteroclitus. The behavioral interactions were observed to determine the prey's vulnerability to predation, and the mode of operation and relative effectiveness of their defenses. Feeding trials and behavioral observations both demonstrated that M. menidia 6–16 mm long preferred Uca minax and Callinectes sapidus zoeae, which are exported from the estuary, to Rhithropanopeus harrisii, Sesarma reticulatum and Palaemonetes pugio, which are retained within estuaries. Pinnotheres ostreum zoeae develop in the lower estuary and fish demonstrated an intermediate preference for the zoeae. Menidia menidia 20–40 mm long showed similar preferences for R. harrisii S. reticulatum, P. ostreum and U. minax as did small silversides. Large-mouthed demersal fish, Fundulus heteroclitus 6–10 mm long, also preferred U. minax to R. harrisii, but more readily preyed on zoeae than did M. menidia. The exported species of zoeae have shorter spines and smaller bodies than do retained zoeae, except P. ostreum which is small, spineless and passively sinks when attacked by fish. Other retained species of zoeae also have postcontact behavioral defenses which enhance the effectiveness of their morphological defenses. Zoeae do not evade attacks by fishes, but fishes quickly learned to avoid zoeae, which increases the effectiveness of the zoeae's antipredatory adaptations.     

Phycomyces: Phototropism and light-growth response to pulse stimuli

The relationship between phototropism and the light-growth response of Phycomyces blakesleeanus (Burgeff) sporangiophores was investigated. After dark adaptation, stage-IVb sporangiophores were exposed to short pulses of unilateral light at 450 nm wavelength. The sporangiophores show a complex reaction to pulses of 30 s duration: maximal positive bending at 3·10^-4 and 10^-1 J m^-2, but negative bending at 30 J m^-2. The fluence dependence for the light-growth response also is complex, but in a different way than for phototropism; the first maximal response occurs at 1.8·10^-3 J m^-2 with a lesser maximum at 30 J m^-2. A hypertropic mutant, L85 (madH), lacks the negative phototropism at 30 J m^-2 but gives results otherwise similar to the wild type. The reciprocity rule was tested for several combinations of fluence rates and pulse durations that ranged from 1 ms to 30 s. Near the threshold fluence (3·10^-5 J m^-2), both responses increase for pulse durations below 67 ms and both have an optimum at 2 ms. At a fluence of 2.4·10^-3 J m^-2, both responses decrease for pulse durations below 67 ms. The hypertropic mutant (madH), investigated for low fluence only, gave similar results. In both strains, the time courses for phototropism and light-growth response, after single short pulses of various durations, show no clear correlation. These results imply that phototropism cannot be caused by linear superposition of localized light-growth responses; rather, they point to redistribution of growth substances as the cause of phototropism.     

Responses of Odonata chromatophores to environmental stimuli

Responses to change in temperature and light intensity were studied in three species of Australian Odonata using time-lapse photography. In each species, responses to temperature are dependent on both the instantaneous temperature and the direction of temperature change. At temperatures below those which produce unstable colour phases, the change to dark phase takes about 9 hr and is constant in rate. The reverse change is directly temperature dependent and can be much more rapid. Responses to change in light intensity are attributable to the heating effect of light rather than to true light sensitivity. All colour changes show wide individual variation in both rate and amount. They are slightly affected by temperature acclimation but are unaffected by prevailing weather, time of year, geographic location, or age.     

Physiological adaptations in response to environmental stress during an n(2)-fixing anabaena bloom

Anabaena spiroides has the ability to maintain intense biomass production for extensive periods in the epilimnion of a small eutrophic lake characterized by conditions shown to cause photooxidative death in a number of other phytoplankton. By the enhancement of carotenoid synthesis chlorophyll a was protected from photooxidation and prevented from catalyzing other photooxidative reactions within the cells. By temporally separating CO(2) and N(2) fixation, maximum utilization of photosynthetically active radiation was achieved. Because CO(2) fixation was more sensitive than N(2) fixation to a high oxygen concentration, the former was maximized during morning hours, before the afternoon buildup of dissolved oxygen. The diurnal partitioning of carbon and N(2) fixation has two additional advantages; possible competition for reductant-generating compounds is minimized, and adequate endogenous pools of carbon skeletons are assured to accept newly fixed ammonia. Hence, Anabaena, far from undergoing photooxidative death, appears to utilize a physiological strategy which allows optimization of radiant energy use for reductive processes and dominance of surface waters and shading of deeper phytoplankton during summer blooms.     

The Arabidopsis WAVY GROWTH 2 protein modulates root bending in response to environmental stimuli

To understand how the direction of root growth changes in response to obstacles, light, and gravity, we characterized an Arabidopsis thaliana mutant, wavy growth 2 (wav2), whose roots show a short-pitch pattern of wavy growth on inclined agar medium. The roots of the wav2 mutant bent with larger curvature than those of the wild-type seedlings in wavy growth and in gravitropic and phototropic responses. The cell file rotations of the root epidermis of wav2-1 in the wavy growth pattern were enhanced in both right-handed and left-handed rotations. WAV2 encodes a protein belonging to the BUD EMERGENCE 46 family with a transmembrane domain at the N terminus and an alpha/beta-hydrolase domain at the C terminus. Expression analyses showed that mRNA of WAV2 was expressed strongly in adult plant roots and seedlings, especially in the root tip, the cell elongation zone, and the stele. Our results suggest that WAV2 is not involved in sensing environmental stimuli but that it negatively regulates stimulus-induced root bending through inhibition of root tip rotation.     

Hsp90 globally targets paused RNA polymerase to regulate gene expression in response to environmental stimuli

The molecular chaperone Heat shock protein 90 (Hsp90) promotes the maturation of several important proteins and plays a key role in development, cancer progression, and evolutionary diversification. By mapping chromatin-binding sites of Hsp90 at high resolution across the Drosophila genome, we uncover an unexpected mechanism by which Hsp90 orchestrates cellular physiology. It localizes near promoters of many coding and noncoding genes including microRNAs. Using computational and biochemical analyses, we find that Hsp90 maintains and optimizes RNA polymerase II pausing via stabilization of the negative elongation factor complex (NELF). Inhibition of Hsp90 leads to upregulation of target genes, and Hsp90 is required for maximal activation of paused genes in Drosophila and mammalian cells in response to environmental stimuli. Our findings add a molecular dimension to the chaperone's functionality with wide ramifications into its roles in health, disease, and evolution.     

Visual ecology of Indian carpenter bees II: adaptations of eyes and ocelli to nocturnal and diurnal lifestyles

Most bees are diurnal, with behaviour that is largely visually mediated, but several groups have made evolutionary shifts to nocturnality, despite having apposition compound eyes unsuited to vision in dim light. We compared the anatomy and optics of the apposition eyes and the ocelli of the nocturnal carpenter bee, Xylocopa tranquebarica, with two sympatric species, the strictly diurnal X. leucothorax and the occasionally crepuscular X. tenuiscapa. The ocelli of the nocturnal X. tranquebarica are unusually large (diameter ca. 1 mm) and poorly focussed. Moreover, their apposition eyes show specific visual adaptations for vision in dim light, including large size, large facets and very wide rhabdoms, which together make these eyes 9 times more sensitive than those of X. tenuiscapa and 27 times more sensitive than those of X. leucothorax. These differences in optical sensitivity are surprisingly small considering that X. tranquebarica can fly on moonless nights when background luminance is as low as 10⁻⁵ cd m⁻², implying that this bee must employ additional visual strategies to forage and find its way back to the nest. These strategies may include photoreceptors with longer integration times and higher contrast gains as well as higher neural summation mechanisms for increasing visual reliability in dim light.     

Scorpion lateral eyes: Extremely sensitive receptors of Zeitgeber stimuli

Summary The circadian rhythm of sensitivity in the median eyes ofAndroctonus australis L. can be entrained by exposure of the lateral eyes to a 24-h light-dark rhythm. Presentation of the Zeitgeber to only the anteriormost one of the lateral eyes sufficed (Fig. 1). However, with illumination of an entire group of lateral eyes (Fig. 2), entrainment was obtained at extremely low light intensities — white light at luminance levels of 10^–4cd · m^–2 (=2.5 · 10^–4 lux, cf. Methods).The relatively less marked circadian rhythm of lateral-eye sensitivity is probably controlled via the optic nerve supplying these eyes (Fig. 4).Supported by the Deutsche Forschungsgemeinschaft (F1 77/5-6 and F1 77/7 Schwerpunktprogramm: Biologie der Zeitmessung)