Transmembrane semaphorin signalling controls laminar stratification in the mammalian retina

In the vertebrate retina, establishment of precise synaptic connections among distinct retinal neuron cell types is critical for processing visual information and for accurate visual perception. Retinal ganglion cells (RGCs), amacrine cells and bipolar cells establish stereotypic neurite arborization patterns to form functional neural circuits in the inner plexiform layer (IPL), a laminar region that is conventionally divided into five major parallel sublaminae. However, the molecular mechanisms governing distinct retinal subtype targeting to specific sublaminae within the IPL remain to be elucidated. Here we show that the transmembrane semaphorin Sema6A signals through its receptor PlexinA4 (PlexA4) to control lamina-specific neuronal stratification in the mouse retina. Expression analyses demonstrate that Sema6A and PlexA4 proteins are expressed in a complementary fashion in the developing retina: Sema6A in most ON sublaminae and PlexA4 in OFF sublaminae of the IPL. Mice with null mutations in PlexA4 or Sema6A exhibit severe defects in stereotypic lamina-specific neurite arborization of tyrosine hydroxylase (TH)-expressing dopaminergic amacrine cells, intrinsically photosensitive RGCs (ipRGCs) and calbindin-positive cells in the IPL. Sema6A and PlexA4 genetically interact in vivo for the regulation of dopaminergic amacrine cell laminar targeting. Therefore, neuronal targeting to subdivisions of the IPL in the mammalian retina is directed by repulsive transmembrane guidance cues present on neuronal processes.     

Vertical interactions across ten parallel, stacked representations in the mammalian retina

The mammalian visual system analyses the world through a set of separate spatio-temporal channels. The organization of these channels begins in the retina, where the precise laminations of both the axon terminals of bipolar cells and the dendritic arborizations of ganglion cells suggests the presence of a vertical stack of neural strata at the inner plexiform layer (IPL). Conversely, many inhibitory amacrine cell classes are multiply or diffusely stratified, indicating that they might convey information between strata. On the basis of the diverse stratification and physiological properties of ganglion cells, it was suggested that the IPL contains a parallel set of representations of the visual world embodied in the strata and conveyed to higher centres by the classes of ganglion cells whose dendrites ramify at that stratum. Here we show that each stratum receives unique and substantively different excitatory and inhibitory neural inputs that are integrated to form at least ten different, parallel space-time spiking outputs. The response properties of these strata are ordered in the time domain. Inhibition through GABAC receptors extracts spatial edges in neural representations and seems to separate the functional properties of the strata. We describe a new form of neuronal interaction that we call 'vertical inhibition' that acts not laterally, but between strata.     

Two types of orientation-sensitive responses of amacrine cells in the mammalian retina.

Neurons sensitive to the orientation of light stimuli exist throughout the mammalian visual system, suggesting that this spatial feature is a fundamental cue used by the brain to decipher visual information. The most peripheral neurons known to show orientation sensitivity are the retinal ganglion cells. Considerable morphological and pharmacological data suggest that the orientation sensitivity of ganglion cells is formed, at least partly, by the amacrine cells, which are laterally oriented interneurons presynaptic to the ganglion cells in the inner plexiform layer. So far there have been few studies of the responses of amacrine cells to oriented visual stimuli and their role in forming orientation-sensitive responses in the retina remains unclear. Here I report the novel finding of a population of amacrine cells in the rabbit retina which are orientation-sensitive. These amacrine cells can be divided into two subtypes, whose orientation sensitivity is manufactured by two distinct mechanisms. The orientation sensitivity of the first subtype of amacrine cell is formed from the interactions of excitatory, centre-receptive field synaptic inputs and inhibitory inputs of opposite polarity, whereas that for cells of the second subtype seems to be the product of a marked asymmetry in their dendritic arbors.     

Melanopsin and rod-cone photoreceptive systems account for all major accessory visual functions in mice

In the mammalian retina, besides the conventional rod-cone system, a melanopsin-associated photoreceptive system exists that conveys photic information for accessory visual functions such as pupillary light reflex and circadian photo-entrainment. On ablation of the melanopsin gene, retinal ganglion cells that normally express melanopsin are no longer intrinsically photosensitive. Furthermore, pupil reflex, light-induced phase delays of the circadian clock and period lengthening of the circadian rhythm in constant light are all partially impaired. Here, we investigated whether additional photoreceptive systems participate in these responses. Using mice lacking rods and cones, we measured the action spectrum for phase-shifting the circadian rhythm of locomotor behaviour. This spectrum matches that for the pupillary light reflex in mice of the same genotype, and that for the intrinsic photosensitivity of the melanopsin-expressing retinal ganglion cells. We have also generated mice lacking melanopsin coupled with disabled rod and cone phototransduction mechanisms. These animals have an intact retina but fail to show any significant pupil reflex, to entrain to light/dark cycles, and to show any masking response to light. Thus, the rod-cone and melanopsin systems together seem to provide all of the photic input for these accessory visual functions.     

Wnt signalling in stem cells and cancer

The canonical Wnt cascade has emerged as a critical regulator of stem cells. In many tissues, activation of Wnt signalling has also been associated with cancer. This has raised the possibility that the tightly regulated self-renewal mediated by Wnt signalling in stem and progenitor cells is subverted in cancer cells to allow malignant proliferation. Insights gained from understanding how the Wnt pathway is integrally involved in both stem cell and cancer cell maintenance and growth in the intestinal, epidermal and haematopoietic systems may serve as a paradigm for understanding the dual nature of self-renewal signals.     

上皮植入性虹膜囊肿34眼治疗分析

分析评价上皮植入性虹膜囊肿发病机理和预防治疗方法。上皮植入性虹膜囊肿的预防最重要的是及时正确地处理角膜创口 ,治疗以微观手术切除效果最佳     

基于Rubber-sheet模型的虹膜识别算法研究

为了实现对虹膜内外边界的精确定位,提出了改进的虹膜图像定位算法.虹膜图像预处理过程主要包括虹膜边界定位、归一化处理和图像增强三部分,其中虹膜图像边界定位是实现虹膜识别的重要前提.首先使用质心探测法确定其二值化虹膜图像的内边界中心,然后再对内边界进行曲线拟合,从而实现对虹膜内边界的定位.使用Canny算子进行边缘检测,确定虹膜图像外边界,完成对虹膜边界的定位.使用Rubber-sheet模型对经过定位的虹膜区域图像进行归一化处理,方便虹膜图像的信息提取和编码匹配.实验证明改进的算法有效提高了虹膜图像预处理效率.     

Nodal signalling in vertebrate development

Communication between cells during early embryogenesis establishes the basic organization of the vertebrate body plan. Recent work suggests that a signalling pathway centering on Nodal, a transforming growth factor beta-related signal, is responsible for many of the events that configure the vertebrate embryo. The activity of Nodal signals is regulated extracellularly by EGF-CFC cofactors and antagonists of the Lefty and Cerberus families of proteins, allowing precise control of mesoderm and endoderm formation, the positioning of the anterior-posterior axis, neural patterning and left-right axis specification.     

Thrombin signalling and protease-activated receptors

How does the coagulation protease thrombin regulate cellular behaviour? The protease-activated receptors (PARs) provide one answer. In concert with the coagulation cascade, these receptors provide an elegant mechanism linking mechanical information in the form of tissue injury or vascular leakage to cellular responses. Roles for PARs are beginning to emerge in haemostasis and thrombosis, inflammation, and perhaps even blood vessel development.     

Photoreceptive net in the mammalian retina. This mesh of cells may explain how some blind mice can still tell day from night

We have discovered an expansive photoreceptive 'net' in the mouse inner retina, visualized by using an antiserum against melanopsin, a likely photopigment. This immunoreactivity is evident in a subset of retinal ganglion cells that morphologically resemble those that project to the suprachiasmatic nucleus (SCN), the site of the primary circadian pacemaker. Our results indicate that this bilayered photoreceptive net is anatomically distinct from the rod and cone photoreceptors of the outer retina, and suggest that it may mediate non-visual photoreceptive tasks such as the regulation of circadian rhythms.     

Inositol phosphates and cell signalling

Inositol 1,4,5-trisphosphate is a second messenger which regulates intracellular calcium both by mobilizing calcium from internal stores and, perhaps indirectly, by stimulating calcium entry. In these actions it may function with its phosphorylated metabolite, inositol 1,3,4,5-tetrakisphosphate. The subtlety of calcium regulation by inositol phosphates is emphasized by recent studies that have revealed oscillations in calcium concentration which are perhaps part of a frequency-encoded second-messenger system.     

Myelin-associated glycoprotein in human retina

The human retina is unmyelinated, but structural similarities have been noted between Müller cells, the main glial cell type of retina, and oligodendrocytes, the myelin-forming cells of the central nervous system. We now show that antibodies against myelin-associated glycoprotein, a minor component of central and peripheral myelin so far found only in myelin and myelin-forming cells, also stain Müller cells. Immunoblot analysis of retinal proteins indicates that the antigen detected is myelin associated glycoprotein. These results suggest a closer relationship between Müller cells and oligodendrocytes than previously suspected and raise questions about the functional role of myelin-associated glycoprotein.     

Radon域虹膜图像数字水印研究

提出了Radon域特征嵌入的虹膜图像数字水印算法.算法提取小波变换的过零表达系数,用于描述虹膜纹理特征,将其编码后作为水印信息嵌入原始虹膜图像.证明了虹膜图像Radon变换的幅频域是一个旋转、平移和缩放的不变域,水印的嵌入选择在这个不变域内进行.水印的检测过程不需要原始图像,是一种盲检测水印算法.实验结果表明,提出的虹膜水印算法对虹膜纹理具有敏感性,可以有效地保护虹膜图像纹理区域不受篡改.同时实验还表明,水印对一般的图像处理和几何失真攻击具有鲁棒性.