Molecular genetics of human color vision

The significant advances in our understanding of color vision has been due to the convergence of information from behavioral and molecular genetic analyses. The molecular biology of the visual pigments; molecular genetic basis of variation in normal and abnormal color vision, and regulation of the genes at the LWS-MWS pigment gene locus are discussed.     

Spectral sensitivities of short- and long-wavelength sensitive cone mechanisms in the frog retina

ERG mass photoreceptor responses were recorded across the isolated, aspartate-perfused retina of the frog, Rana temporaria, in order to determine spectral sensitivities of cones. Cone responses were distinguished from rod responses by their faster kinetics, and responses from different cone types were isolated by selective background adaptation. Our main finding is that of a novel short-wavelength sensitive cone population peaking at about 431 nm. Further, we find that the sensitivity spectrum of the dominant long-wavelength sensitive cone population fully accounts for the most common type of photopic ganglion cell spectrum. Both can be described by a nomogram with λ_max= 562 nm. This resolves a long-standing apparent conflict between cone absorbance spectra and ganglion cell sensitivities. Including the 502 nm cones previously described by microspectrophotometry, the frog possesses a collection of cones that could support trichromatic photopic vision.     

先天性红绿色觉异常基因缺失与杂种基因融合位点分析

目的　研究先天性红绿色觉异常基因缺失与杂种基因融合位点。方法　收集１１ 例红色觉异常、１９ 例绿色觉异常和５ 名正常人的白细胞基因组 Ｄ Ｎ Ａ,分别用 Ｐ Ｃ Ｒ 法扩增每人的红和绿色觉基因的启动子和外显子２ 、３ 、４ 和５ ,应用异源双链 Ｓ Ｓ Ｃ Ｐ 法分析 Ｐ Ｃ Ｒ 产物,用已知序列的红与绿色觉基因产物作标准,确定待检个体红或绿色觉基因的来源与各部分的组成。结果　３０ 例红与绿色觉异常患者中１４ 例可检测到杂种基因,７ 例完全缺失绿色觉基因。杂种基因融合位点分别在外显子１ ～内含子１（４ 例） 、内含子２ ～３（５ 例） 和内含子４（５ 例） 。结论　外显子３ 及其邻近的内含子２ 和３ 仍是常见的融合位点,但在其它部位发生的融合也不少见。     

The molecular basis of dichromatic color vision in males with multiple red and green visual pigment genes.

We investigated the genotypic variation in 50 red-green color vision deficient males (27 deuteranopes and 23 protanopes) of middle European ancestry who possess multiple genes in the X-linked photopigment gene array. We have previously shown that only the first two genes of the array are expressed and contribute to the color vision phenotype. Therefore, the hypothesis is that the first two genes possessed by multigene-dichromats encode pigments of identical or nearly identical spectral sensitivity: one gene normal (R or G) and the other a hybrid (G/R or R/G). The spectral sensitivities of the encoded pigments were inferred from published in vitro and in vivo data. The color vision phenotype was assessed by standard anomaloscopy. Most genotypes (92%) included hybrid genes whose sequence and position and whose encoded pigment correlated exactly with the phenotype. However, one and possibly two of the protanopes had gene arrays consistent with protanomaly rather than protanopia, since two spectrally different pigments may be encoded by their arrays. Two of the deuteranopes had only R- and G-photopigment genes, without any detectable G/R-hybrid genes or any as-of-yet identified point mutation or coding/promoter sequence deletions. Further, an unexpectedly high number of multigene-deuteranopes (11%) had the C203R mutation in their most upstream G-pigment gene, suggesting a founder effect of middle European origin for this mutation. About half of the protanopes possessed an upstream R/G-hybrid gene with different exon 2 coding sequences than their downstream G-pigment gene(s), which is inconsistent with published data implying that a single amino acid substitution in exon 2 can confer red-green color discrimination capacity on multigene-protans by altering the optical density of the cones.     

Collicular function in human vision

Summary Threshold elevation in the periphery of the visual field as a consequence of repetitive stimulation can be abolished by stimulating a mirror-symmetric position in the contralateral visual half-field. A patient suffering from a congenital malformation of the right superior colliculus did not exhibit threshold elevation when stimulated repeatedly in the left visual field. Stimulation in the right visual half-field resulted in the usually observed threshold elevation, but stimulating a mirror-symmetric position in the left visual half-field did not abolish threshold elevation in the right half-field. These observations suggest that: (a) threshold elevation probably occurs as a consequence of collicular adaptation and (b) the mirror-symmetrically organized interhemispheric interaction is mediated at the collicular level.This work was supported by the Deutsche Forschungsgemeinschaft     

Slow-movement sensitivity in the human field of vision

The movement detecting channels are observed to be activated by different speeds of moving targets in different zones of the human visual field. In the most nasal peripheral field, horizontally moving targets were detected more easily than those moving in any other direction.     

Blue-sensitive cones in the primate retina: microspectrophotometry of the visual pigment

Summary Direct absorbance and bleaching absorbance- difference spectra were obtained using a photon-counting microspectrophotometer from the outer segments of ten blue-sensitive cones of macaque monkeys. The peak wavelength (_max) of the direct measurements was 426±3.4 nm, whereas the _max of the bleaching difference was 434±6.6 nm. We consider these values to be upper and lower bounds since both measurements may be shifted in opposite directions by wavelength-dependent effects. Therefore, the true peak sensitivity must be close to 430 nm.     

Artificial vision support system (AVS2) for improved prosthetic vision

State-of-the-art and upcoming camera-driven, implanted artificial vision systems provide only tens to hundreds of electrodes, affording only limited visual perception for blind subjects. Therefore, real time image processing is crucial to enhance and optimize this limited perception. Since tens or hundreds of pixels/electrodes allow only for a very crude approximation of the typically megapixel optical resolution of the external camera image feed, the preservation and enhancement of contrast differences and transitions, such as edges, are especially important compared to picture details such as object texture. An Artificial Vision Support System (AVS²) is devised that displays the captured video stream in a pixelation conforming to the dimension of the epi-retinal implant electrode array. AVS², using efficient image processing modules, modifies the captured video stream in real time, enhancing ‘present but hidden’ objects to overcome inadequacies or extremes in the camera imagery. As a result, visual prosthesis carriers may now be able to discern such objects in their ‘field-of-view’, thus enabling mobility in environments that would otherwise be too hazardous to navigate. The image processing modules can be engaged repeatedly in a user-defined order, which is a unique capability. AVS² is directly applicable to any artificial vision system that is based on an imaging modality (video, infrared, sound, ultrasound, microwave, radar, etc.) as the first step in the stimulation/processing cascade, such as: retinal implants (i.e. epi-retinal, sub-retinal, suprachoroidal), optic nerve implants, cortical implants, electric tongue stimulators, or tactile stimulators.     

The molecular basis of human hypogonadotropic hypogonadism.

Patients with hypogonadotropic hypogonadism (HH) present with delayed puberty, infertility, and low serum gonadotropins. The molecular basis for most cases of HH is unknown, but single gene mutations have been described for some hypothalamic and pituitary genes. Kallmann syndrome due to KAL gene mutations and adrenal hypoplasia congenita/HH caused by AHC gene mutations are both X-linked recessive disorders. Mutations in the gonadotropin releasing hormone receptor, leptin, and the leptin receptor cause autosomal recessive HH. In addition, isolated deficiencies of follicle stimulating hormone and luteinizing hormone in the corresponding specific beta-subunit genes and PROP1 gene mutations represent pituitary deficiency states, resulting in a phenotype of HH. Despite these remarkable advances in our understanding of human HH, the cause of approximately 90% remains unknown.     

Temporal frequency characteristics of spatial interaction in human vision

Summary In psychophysical experiments the bright-dark contrast effects observed in a steady test-field were measured as a function of the temporal frequency of an inducing-field modulated symmetrically about the test-field luminance. The frequency-contrast functions obtained from these measurements were interpreted as reflecting the temporal frequency characteristics of the lateral pathways within the B and D systems (the on-center and off-center neurons) in human vision. Psychophysical evidence is further presented that the lateral neural pathways have lower temporal cut-off frequencies than the straight-through pathways. The results are discussed in terms of the frequency characteristics of the center and surround of the receptive fields of on-center and off-center neurons. It is doubtful, however, whether the psychophysical results can be fully explained by the properties of the single-unit receptive field mechanism.     

The utilization of visual feedback from peripheral and central vision in the control of direction

Past research has demonstrated that both peripheral and central vision play an important role in the control of movement direction. However, it has been unclear whether the benefits of these sources of information are due to adjustments in the limb trajectory during movement execution (i.e., online) or modification in motor commands prior to movement initiation (i.e., offline). In the present paper, we analyzed the variability in limb trajectories in a directional aiming task to examine the relative contributions of peripheral and central vision in both the planning and execution of movements. The point of gaze was manipulated to vary where in the limb trajectory information was gained from central and peripheral vision. Analysis of the variability in directional error at various stages of the movement revealed that participants utilized information from early in the trajectory during movement execution when it appeared in both peripheral and central visual fields. Information from late in the trajectory was used offline to improve the programming of subsequent movements regardless of where this information was available in the visual field.     

Search for the molecular basis of morphological variation in Mycobacterium avium.

Isolates of Mycobacterium avium exhibit three different colonial variations: smooth domed (SmD), smooth transparent (SmT), and rough (Rg). Because the discrimination between morphotypes is founded on morphological rather than molecular principles and because of the absence of consensus over the relevance of morphology to pathogenesis and drug sensitivity, a comparative study at the protein level was undertaken. By direct immunization of BALB/c mice with the soluble sonicate of one of the morphotypes of M. avium serovar 2, eight monoclonal antibodies (MAbs) were identified, of which one was M. avium specific. Cross immunization of syngeneic mice with serum-absorbed antigens allowed the generation of 15 further MAbs; 11 were M. avium or M. avium complex specific, but none of them was morphotype specific. Subcellular fractions analyzed by electrophoresis showed similar profiles, with the exception of a cytosolic protein with a relative molecular mass of ca. 66 kDa (protein SmT 66), which was most highly expressed in SmT variants of M. avium serotypes 2 and 4. Because a well-known, ubiquitous stress-heat shock protein (hsp65) has a similar molecular mass, protein SmT 66 was compared with hsp65. Western blot (immunoblot) analyses using several cross-reacting MAbs and N-terminal amino acid sequencing established that this protein was not the ubiquitous stress protein. Thus, SmT 66 is the first product to be described which might be associated with the SmT morphotype.     

Inhibition,disinhibition, and summation among orientation detectors in human vision

Summary A vertical test line viewed together with an oblique inducing line appears to be tilted in the opposite direction (orientation contrast); a similar effect results from adapting to an oblique line before presenting the test line (tilt after-effect). The error in perceived orientation caused by a clockwise tilted inducing line may be partially cancelled by a second clockwise tilted inducing line; likewise, adapting to a configuration of two clockwise orientations gives weaker tilt after-effects than adapting to the more effective of the two orientations alone. The angular functions of these disinhibitory effects mirror the angular functions of the principal effects. However, combining tilt after-effect and simultaneous contrast in a disinhibition design by having the subject first adapt to a clockwise orientation and then presenting the test line together with a clockwise inducing line results in partial summation rather than disinhibition. The results are consistent with Carpenter's and Blakemore's (1973) hypothesis that orientation contrast and the tilt after-effect are manifestations of cortical inhibition in a network of inhibitory, recurrent lateral connections between cortical orientation detectors. After-effects must be due to prolonged inhibition, probably caused by a sensitivity change in previously inhibited detectors.Parts of this paper were presented at the annual meeting of the Association for Research in Vision and Ophthalmology, Sarasota, Florida, 30 April to 5 May, 1979, and the 3rd European Conference on Visual Perception, Brighton, England, 3 to 6 September, 1980     

仿真假体视觉下的人脸识别研究进展

目的：综述基于仿真假体视觉的人脸识别研究的主要进展。方法：回顾了近年来各研究小组基于仿真假体视觉的人脸识别研究进展,讨论假体视觉下人脸识别的可能性,分析了假体视觉下人脸识别的影响因素。结果：在仿真假体视觉下,分辨率和缺失率是影响人脸识别的主要因素,分辨率增加或是缺失率减小,对人脸的识别率有显著提高;其它光幻视参数中,一定程度内的灰度提高对假体下的人脸识别率有显著提高,而点大小、点间隙、对比度对其影响稍小,正方形的光幻视阵列排布的识别率高于六边形和极坐标排布。另外,图像处理策略如基于感兴趣区域的放大和对比度增强等,能帮助被试进行人脸识别。结论：由心理物理学方法得出,在假体视觉下,仍能完成基本的人脸识别任务;改变光幻视的参数或图像处理策略,会影响识别率。这些结果将帮助研究者们优化视觉假体中的信息处理和图像处理策略,并为术后康复训练提供了实验理论依据。     

The molecular basis of allergenicity

Allergens are mostly innocuous antigens that elicit powerful T helper cell type 2 (Th2) responses leading to hyper-immunoglobulin E (IgE) production and allergy. Research carried out over several years has highlighted the possible role of the inherent protease activity, surface features and glycosylation patterns of allergens in the engagement of a Th2 signalling pathway. It is thought that allergens possess common features and patterns that enable them to be recognized by innate immune defences as Th2-inducing antigens. These events are further amplified by proteolytically active allergens through digestion of cell surface molecules involved in regulating innate and adaptive immune functions, favouring Th2 responses. A greater understanding of the molecular features that make proteins allergenic will help define new therapeutic targets aimed at blocking allergen recognition and protease activity.