Characterisation of the RNA interference response against the long-wavelength receptor of the honeybee

Targeted knock-down is the method of choice to advance the study of sensory and brain functions in the honeybee by using molecular techniques. Here we report the results of a first attempt to interfere with the function of a visual receptor, the long-wavelength-sensitive (L-) photoreceptor. RNA interference to inhibit this receptor led to a reduction of the respective mRNA and protein. The interference effect was limited in time and space, and its induction depended on the time of the day most probably because of natural daily variations in opsin levels. The inhibition did not effectively change the physiological properties of the retina. Possible constraints and implications of this method for the study of the bee's visual system are discussed. Overall this study underpins the usefulness and feasibility of RNA interference as manipulation tool in insect brain research.     

Role of olfaction and vision in homing behaviour of black rockfish Sebastes inermis

How fish find their original habitat and natal home remains an unsolved riddle of animal behaviour. Despite extensive efforts to study the homing behaviour of diadromous fish, relatively little attention has been paid to that of non-diadromous marine fish. Among these, most rockfish of the genus Sebastes exhibit homing ability and/or a strong fidelity to their habitats. However, how these rockfish detect the homeward direction has not been clarified. The goal of the present research was to investigate the sensory mechanisms involved in the homing behaviour of the black rockfish Sebastes inermis, using acoustic telemetry. Vision-blocked or olfactory-ablated rockfish were released in natural waters and their homing behaviours compared with those of intact or control individuals. Blind rockfish showed homing from both inside and outside their habitat. The time taken by blind fish to reach their home habitat was not significantly different from that of the control fish. In contrast, most olfactory-ablated fish did not successfully reach their original habitat. Our results indicate that black rockfish predominantly use the olfactory sense in their homing behaviour.     

Toll-like receptor 3 is required for development of retinopathy caused by impaired all-trans-retinal clearance in mice

Chronic inflammation is an important component that contributes to many age-related neurodegenerative diseases, including macular degeneration. Here, we report a role for toll-like receptor 3 (TLR3) in cone-rod dystrophy (CORD) of mice lacking ATP-binding cassette transporter 4 (ABCA4) and retinol dehydrogenase 8 (RDH8), proteins critical for all-trans-retinal clearance in the retina. Increased expression of toll-like receptor-signaling elements and inflammatory changes were observed in Rdh8(-/-)Abca4(-/-) eyes by RNA expression analysis. Unlike 3-month-old Rdh8(-/-)Abca4(-/-) mice that developed CORD, 6-month-old Tlr3(-/-)Rdh8(-/-)Abca4(-/-) mice did not evidence an abnormal retinal phenotype. Light-induced retinal degeneration in Tlr3(-/-)Rdh8(-/-)Abca4(-/-) mice was milder than that in Rdh8(-/-)Abca4(-/-) mice, and a 2-fold increased TLR3 expression was detected in light-illuminated retinas of Rdh8(-/-)Abca4(-/-) mice compared with nonilluminated retinas. Poly(I-C), a TLR3 ligand, caused caspase-8-independent cellular apoptosis. Whereas poly(I-C) induced retinal cell death in Rdh8(-/-)Abca4(-/-) and WT mice both in vivo and ex vivo, this was not seen in mice lacking Tlr3. Far fewer invasive macrophage/microglial cells in the subretinal space and weaker activation of Muller glial cells were exhibited by Tlr3(-/-)Rdh8(-/-) Abca4(-/-) mice compared with Rdh8(-/-)Abca4(-/-) mice at 3 and 6 months of age, indicating that loss of TLR3 inhibits local inflammation in the retina. Both poly(I-C) and endogenous products emanating from dying/dead retinal cells induced NF-κB and IRF3 activation. These findings demonstrate that endogenous products from degenerating retina stimulate TLR3 that causes cellular apoptosis and retinal inflammation and that loss of TLR3 protects mice from CORD.     

Role of bulk water in hydrolysis of the rhodopsin chromophore

Rhodopsin (Rho) is a prototypical G protein-coupled receptor that changes from an inactive conformational state to a G protein-activating state as a consequence of its retinal chromophore isomerization, 11-cis-retinal → all-trans-retinal. The photoisomerized chromophore covalently linked to Lys(296) by a Schiff base is subsequently hydrolyzed, but little is known about this reaction. Recent research indicates a significant role for tightly bound transmembrane water molecules in the Rho activation process. Atomic structures of Rho and hydroxyl radical footprinting reveal ordered waters within Rho transmembrane helices that are located close to highly conserved and functionally important receptor residues, forming a hydrogen bond network. Using (18)O-labeled H(2)O, we now report that water from bulk solvent, but not tightly bound water, is involved in the hydrolytic release of chromophore upon Rho activation by light. Moreover, small molecules (and presumably, water) enter the Rho structure from the cytoplasmic side of the membrane. Thus, this work indicates two distinct origins of water vital for Rho function.     

Isolevuglandins and mitochondrial enzymes in the retina: mass spectrometry detection of post-translational modification of sterol-metabolizing CYP27A1

We report the first peptide mapping and sequencing of an in vivo isolevuglandin-modified protein. Mitochondrial cytochrome P450 27A1 (CYP27A1) is a ubiquitous multifunctional sterol C27-hydroxylase that eliminates cholesterol and likely 7-ketocholesterol from the retina and many other tissues. We investigated the post-translational modification of this protein with isolevuglandins, arachidonate oxidation products. Treatment of purified recombinant CYP27A1 with authentic iso[4]levuglandin E(2) (iso[4]LGE(2)) in vitro diminished enzyme activity in a time- and phospholipid-dependent manner. A multiple reaction monitoring protocol was then developed to identify the sites and extent of iso[4]LGE(2) adduction. CYP27A1 exhibited only three Lys residues, Lys(134), Lys(358), and Lys(476), that readily interact with iso[4]LGE(2) in vitro. Such selective modification enabled the generation of an internal standard, (15)N-labeled CYP27A1 modified with iso[4]LGE(2), for the subsequent analysis of a human retinal sample. Two multiple reaction monitoring transitions arising from the peptide AVLK(358)(-C(20)H(26)O(3))ETLR in the retinal sample were observed that co-eluted with the corresponding two (15)N transitions from the supplemented standard. These data demonstrate that modified CYP27A1 is present in the retina. We suggest that such protein modification impairs sterol elimination and likely has other pathological sequelae. We also propose that the post-translational modifications identified in CYP27A1 exemplify a general mechanism whereby oxidative stress and inflammation deleteriously affect protein function, contributing, for example, to cholesterol-rich lesions associated with age-related macular degeneration and cardiovascular disease. The proteomic protocols developed in this study are generally applicable to characterization of lipid-derived oxidative protein modifications occurring in vivo, including proteins bound to membranes.     

Differential control of light-dark adaptation in the ocelli and compound eyes of Triatoma infestans

The adaptation to light of compound eyes in insects has been extensively documented and their adaptive role is well understood. Much less attention has been paid, however, to the control of ocelli sensitivity, a study which could help us to understand the functional role of these simple eyes. We analyzed the dynamic changes in the distribution of screening pigments which occur in the ocelli of the haematophagous bug, Triatoma infestans, when the insects are subjected either to light/dark cycles (LD), to constant darkness (DD) or constant light (LL). We then compared these changes with those occurring in the compound eyes of the same individuals and found that, while compound eyes are subject to the control of an endogenous circadian clock, the adaptation of the ocelli is entirely dependent on environmental illumination. In addition, we have observed that environmental temperature is not involved in the control of screening pigments in either ocelli or compound eyes as a direct stimulus, nor as a Zeitgeber. The existence of a differential control in the components of the dual visual system represents an adaptive advantage in the adjustment of visual sensitivity in insects exposed to quick changes in lighting conditions in their natural habitat. We discuss the implications of our findings with regards to the biology of triatomines and with respect to the general understanding the functional role of insect ocelli.     

Sparse Spatial Sampling for the Computation of Motion in Multiple Stages

The avian retino-tecto-rotundal pathway plays a central role in motion analysis and features complex connectivity. Yet, the relation between the pathway’s structural arrangement and motion computation has remained elusive. For an important type of tectal wide-field neuron, the stratum griseum centrale type I (SGC-I) neuron, we quantified its structure and found a spatially sparse but extensive sampling of the retinal projection. A computational investigation revealed that these structural properties enhance the neuron’s sensitivity to change, a behaviorally important stimulus attribute, while preserving information about the stimulus location in the SGC-I population activity. Furthermore, the SGC-I neurons project with an interdigitating topography to the nucleus rotundus, where the direction of motion is computed. We showed that, for accurate direction-of-motion estimation, the interdigitating projection of tectal wide-field neurons requires a two-stage rotundal algorithm, where the second rotundal stage estimates the direction of motion from the change in the relative stimulus position represented in the first stage     

用余光感知图形的魅力

正2016年第6期Science China Life Sciences发表了一篇题名为《用外周视野感知完美的Dora Maar》的文章[1],报道了成都大学美术学院与中国科学院生物物理研究所视觉科学与艺术的跨学科合作研究结果.该研究显示(图1a),让被试盯着圆形外的注视点,同时利用外围视觉感知图形,在用余光观察圆形的过程中,位于外围视野中的圆形靠近被试者鼻侧的边缘部分被明显压缩,外周视野对圆形产生了非对称的视觉感受(图1b).如果以毕加索的油画《朵拉·玛尔》(Dora Maar)     

Post-embryonic photoreceptor development and dark/light adaptation in the spittle bug Philaenus spumarius (L.) (Homoptera, Cercopidae)

The aims of this paper have been to describe (1) the general structure of the compound eye of the spittle bug Philaenus spumarius, (2) the eye's post-embryonic development, (3) photomechanical changes upon dark/light adaptation in the eye, and (4) how leaving the semi-aquatic foam bubble and turning into an adult affects the organization of the eye. Spittle bugs, irrespective of size or sex, possess apposition type compound eyes. The eye's major components (i.e. facet, cornea, cone and rhabdom) grow rather isometrically from the smallest nymph to the adult. Photomechanical changes can occur during both nymphal and adult phases and manifest themselves through pigment granules and mitochondria migrating to and away from the rhabdom, and rhabdom diameters varying with time of day and ambient light level. When a nymph transforms into an adult, its compound eyes’ dorsoventral axes widen, facet diameters increase, facet shapes turn from circular to pentagonal and hexagonal, the cornea thickens and the rhabdoms become thinner. The agile adults, free from the foam that surrounds the nymphs, can be expected to need their vision more than the nymphs, and the changes in eye structure do, indeed, indicate that the adults have superior visual acuity. A thicker cornea in the adults reduces water loss and protects the compound eye from mechanical and light-induced damage: protection given to the nymphs by their foam bubbles.     

Prey size selection and distance estimation in foraging adult dragonflies

To determine whether perching dragonflies visually assess the distance to potential prey items, we presented artificial prey, glass beads suspended from fine wires, to perching dragonflies in the field. We videotaped the responses of freely foraging dragonflies (Libellula luctuosa and Sympetrum vicinum—Odonata, suborder Anisoptera) to beads ranging from 0.5 mm to 8 mm in diameter, recording whether or not the dragonflies took off after the beads, and if so, at what distance. Our results indicated that dragonflies were highly selective for bead size. Furthermore, the smaller Sympetrum preferred beads of smaller size and the larger Libellula preferred larger beads. Each species rejected beads as large or larger than their heads, even when the beads subtended the same visual angles as the smaller, attractive beads. Since bead size cannot be determined without reference to distance, we conclude that dragonflies are able to estimate the distance to potential prey items. The range over which they estimate distance is about 1 m for the larger Libellula and 70 cm for the smaller Sympetrum. The mechanism of distance estimation is unknown, but it probably includes both stereopsis and the motion parallax produced by head movements.