Simultaneous Expression of UV and Violet SWS1 Opsins Expands the Visual Palette in a Group of Freshwater Snakes

Snakes are known to express a rod visual opsin and two cone opsins, only (SWS1, LWS), a reduced palette resulting from their supposedly fossorial origins. Dipsadid snakes in the genus Helicops are highly visual predators that successfully invaded freshwater habitats from ancestral terrestrial-only habitats. Here, we report the first case of multiple SWS1 visual pigments in a vertebrate, simultaneously expressed in different photoreceptors and conferring both UV and violet sensitivity to Helicops snakes. Molecular analysis and in vitro expression confirmed the presence of two functional SWS1 opsins, likely the result of recent gene duplication. Evolutionary analyses indicate that each sws1 variant has undergone different evolutionary paths with strong purifying selection acting on the UV-sensitive copy and d_N/d_S ∼1 on the violet-sensitive copy. Site-directed mutagenesis points to the functional role of a single amino acid substitution, Phe86Val, in the large spectral shift between UV and violet opsins. In addition, higher densities of photoreceptors and SWS1 cones in the ventral retina suggest improved acuity in the upper visual field possibly correlated with visually guided behaviors. The expanded visual opsin repertoire and specialized retinal architecture are likely to improve photon uptake in underwater and terrestrial environments, and provide the neural substrate for a gain in chromatic discrimination, potentially conferring unique color vision in the UV–violet range. Our findings highlight the innovative solutions undertaken by a highly specialized lineage to tackle the challenges imposed by the invasion of novel photic environments and the extraordinary diversity of evolutionary trajectories taken by visual opsin-based perception in vertebrates.     

Neuronal basis for spectral song discrimination in the bushcricket Tettigonia cantans

Previous experiments demonstrated that in choice situations female Tettigonia cantans prefer signals with the conspecific spectrum over signals with the spectrum of the sibling species T. viridissima, whose signals lack the T. cantans-typical 8-kHz component but are otherwise identical in spectral composition. The underlying neuronal mechanisms were investigated using whole-nerve recordings of the tympanal nerve. Hearing thresholds did not differ significantly between the species in the range between 7 and 25 kHz. The responses of the tympanic nerve at 30 dB above threshold did, however, differ significantly between the species. While in T. viridissima response amplitudes did not differ between 7 and 12 kHz, in T. cantans responses at 8 kHz were significantly larger than at 10 and 12 kHz. Since possible influences of axonal diameters on response magnitudes were excluded, these results indicate that in T. cantans more receptor cells are tuned to 8 kHz than to 10–12 kHz, while in T. viridissima tuning of receptor cells is more evenly distributed. The higher response magnitude in T. cantans at 8 kHz than at 10–12 kHz is equivalent to an amplitude difference of 3.8–7 dB, which agrees well with previous behavioural estimates. Accepted: 13 January 1999     

氮氧自由基自旋探针R1在特定空间位点上对bacteriorhodopsin产生颜色调谐效应的机理分析

蛋白质结构研究中的氮氧自由基自旋探针R1,在特定的空间位置上会对bacteriorhodopsin的结构与功能产生影响。该文作者发现:将bacteriorhodopsin中远离视黄醛的第192位Gly替换为自旋探针R1后,产生了显著的颜色调谐,最大吸收峰有28nm的蓝移。但用R1替换Gly192邻近的Gly195和Ala196,未产生颜色调谐效应;替换螺旋E末端的Val130和Tyr131,以及螺旋B末端的Leu62,均无颜色调谐。进一步表征bacteriorhodopsin光循环中间体O和M的衰减过程发现:R1替换前,Gly192Cys(+)的O态衰减寿命约为847.7ms;但替换后,其衰减显著加快至308.2ms。M态的衰减寿命在R1替换后反而显著延长,尤其是慢组分Ms从24.8ms延长至83.6ms。Gly192R1的顺磁共振信号揭示:该位置上的R1处于低运动性状态,表明R1可能与局部环境的结构组分发生了直接作用。晶体结构分析发现:R1可能直接与质子传递通道中的三体水分子作用。由于三体水分子通过长程的氢键网络与视黄醛活性中心相连,并且参与质子在bacteriorhodopsin中的传递,因此自旋探针R1...     

Representational drift in the mouse visual cortex

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An integrated approach for identification of exon locations using recursive Gauss Newton tuned adaptive Kaiser window

Identification of exon location in a DNA sequence has been considered as the most demanding and challenging research topic in the field of Bioinformatics. This work proposes a robust approach combining the Trigonometric mapping with Adaptive tuned Kaiser Windowing approach for locating the protein coding regions (EXONS) in a genetic sequence. For better convergence as well as improved accurateness, the side lobe height control parameter (β) of Kaiser Window in the proposed algorithm is made adaptive to track the changing dynamics of the genetic sequence. This yields better tracking potential of the anticipated Adaptive Kaiser algorithm as it uses the recursive Gauss Newton tuning which in turn utilizes the covariance of the error signal to tune the β factor which has been shown through numerous simulation results under a variety of practical test conditions. A detailed comparative analysis with the existing mapping schemes, windowing techniques, and other signal processing methods like SVD, AN, DFT, STDFT, WT, and ST has also been included in the paper to focus on the strength and efficiency of the proposed approach. Moreover, some critical performance parameters have been computed using the proposed approach to investigate the effectiveness and robustness of the algorithm. In addition to this, the proposed approach has also been successfully applied on a number of benchmark gene sets like Musmusculus, Homosapiens, and C. elegans, etc., where the proposed approach revealed efficient prediction of exon location in contrast to the other existing mapping methods.     

Frequency responses of cat rapidly adapting mechanoreceptive fibers

The frequency responses of 11 rapidly adapting (RA) fibers in cat were studied by representing the average firing rate as a function of sinusoidal stimulus amplitude and stimulus frequency. Specifically, rate-intensity functions at different stimulation frequencies were fitted by four-parameter (a₀, a₁, a₂, a₃), piece-wise linear functions using nonlinear regression (n = 59; R² > 0.877). Rate-intensity functions at intermediate frequencies were found by linear interpolation. The result of this analysis is rate–amplitude–frequency functions plotted as two-dimensional surfaces. The surfaces consist of five regions separated and sufficiently defined by four space curves. At 14 different frequencies, the statistical distribution of each rate-intensity-function parameter could be approximated by a particular lognormal distribution (n = 56; R² > 0.796). The Kolmogorov–Smirnov test fails to reject this hypothesis for each combination of frequency and parameter (56 tests; p > 0.39). Therefore, at a given frequency, the variation of the parameters can be represented by lognormal distributions with specific means and standard deviations. Responses of six RA fibers, which are different from the data-set used for modeling, were compared with the stochastic model at different frequencies. The parameters of those fibers were tested against the null hypotheses that they were sampled from the particular parameter distributions dictated by the model. The Kolmogorov–Smirnov test fails to reject all the hypotheses at the α = 0.05 level (44 tests). At the α = 0.10 level, only a few test parameters were found to be departing from the model (a₀ and a₁ at 5?Hz; a₂ at 20?Hz; a₂ and a₃ at 50?Hz). The remaining test parameters could be accurately described by the model. Having confirmed the validity of the model, the logarithmic means and the logarithmic standard deviations of the lognormally distributed rate-intensity-function parameters were estimated in the frequency range of 4–200?Hz. The rate–amplitude–frequency surfaces sampled from the established stochastic model completely characterize the rate responses of RA fibers to sinusoidal stimuli and are superior to tuning curves which require selecting criterion responses. The current rate-response model is promising for future computational work, especially on population modeling.     

Carotenoids from the crimson and maroon plumages of Old World orioles (Oriolidae)

Recent analyses of the orange, red, and purple plumages of cotingas (Cotingidae) and broadbills (Eurylaimidae) revealed the presence of novel carotenoid molecules, suggesting that the diversity of pigments and the metabolic transformations they undergo are not yet fully understood. Two Old World orioles, the Black-and-Crimson Oriole Oriolus cruentus, and the Maroon Oriole Oriolus traillii, exhibit plumage colors that are similar to those of some cotingas and broadbills. To determine if these oriole plumage colors are produced by the same carotenoids or with other molecules, we used high-performance liquid chromatography (HPLC), mass spectrometry, and chemical analyses. The data show that the bright red feathers of O. cruentus contain a suite of keto-carotenoids commonly found in avian plumages, including canthaxanthin, adonirubin, astaxanthin, papilioerythrinone, and α-doradexanthin. The maroon feathers of O. traillii were found to contain canthaxanthin, α-doradexanthin, and one novel carotenoid, 3′,4-dihydroxy-ε,ε-carotene-3-one, which we have termed “4-hydroxy-canary xanthophyll A.” In this paper we propose the metabolic pathways by which these pigments are formed. This work advances our understanding of the evolution of carotenoid metabolism in birds and the mechanisms by which birds achieve their vivid plumage colorations.