The Nymphal Eyes of Parabuthus transvaalicus Purcell, 1899 (Buthidae): An Accessory Lateral Eye in a Scorpion

In P. transvaalicus nymphs, 5 pairs of lateral ocelli each composed of a corneal lens, R-cell units forming a latticed rhabdom, arhabdomeric cells and pigment cells are present. In addition, we found a pair of unpigmented accessory sense organs situated ventroposteriorly to the lateral ocelli in prenymphs as well as in first nymphs. They are composed of primary, rhabdomeric sensory cells, and we infer that they represent a second type of lateral eye. They also comprise sensory units, but lenses and screening pigment are lacking. Their position and cellular architecture corresponds well with that of the “rudimentary” lateral eye of the xiphosuran, Limulus. The occurrence of a bipartite lateral visual system in Chelicerata and Arthropoda is discussed.     

Aggregation of crystallins induced by pulsed laser UV light (308 nm)

Here we compile and analyze the data on photoaggregation of a model protein carboanhydrase and the main eye lens proteins α-, β-, γ-crystallins under the action of pulsed UV irradiation from a Xe-Cl laser (308 nm) with broad variation of pulse energy density and repetition rate. The aggregation efficacy proves to be a nonlinear function of these parameters and protein concentration. A theoretical model is proposed that qualitatively explains the experimental data. It is shown that N-arm-truncated βA3-crystallin is more prone to UV-induced aggregation than the full-sized protein; such defects caused by mutation or aging may aggravate the development of lenticular opacity. Analyzed is the effect of some low-molecular compounds on the aggregation of β-crystallin and its mixture with α-crystallin. A combination of short peptides prepared on this basis markedly impedes crystallin aggregation and retards the development of UV-induced cataract in rats.     

Age-dependent protein modifications and declining proteasome activity in the human lens

The proteasome is known to be the main enzymatic complex responsible for the intracellular degradation of altered proteins, and the age-related accumulation of modified lens proteins is associated to the formation of cataracts. The aim of this study was to determine whether the human lens proteasome becomes functionally impaired with age. The soluble and insoluble protein fractions of human lenses corresponding to various age-groups were characterized in terms of their levels of glyco-oxidative damage and found to show increasing anti-carboxymethyl-lysine immunoreactivity with age. Concomitantly, decreasing proteasome contents and peptidase activities were observed in the water-soluble fraction. The fact that peptidylglutamyl-peptide hydrolase activity is most severely affected with age suggests that specific changes are undergone by the proteasome itself. In particular, increasing levels of carboxymethylation were observed with age in the proteasome. It was concluded that the lower levels of soluble active enzymatic complex present in elderly lenses and the post-translational modifications affecting the proteasome may at least partly explain the decrease in proteasome activity and the concomitant accumulation of carboxymethylated and ubiquitinated proteins which occur with age.     

HPM长期辐照的眼生物效应研究

目的：研究高功率微波（HPM）在不同平均功率和不同重复频率条件下长期多次照射对眼组织结构的生物效应,为我国HPM安全防护提供生物学依据。方法：采用自行研制的HPM效应模拟源远场平面波（峰值功率密度50W／cm^2）分3个不同平均功率水平,每天6min持续照射1个月,并在照后5个时间点通过眼底镜、裂隙灯观察、组织病理学方法等研究HPM长期照射对动物眼重要部位结构的生物效应。结果：HPM照射后眼角膜、晶状体、眼底等组织结构都出现了不同程度的病理变化,并呈现出一定的时效和量效关系;其中角膜病变依剂量不同可分别于照后2月到照后6月恢复正常,而晶状体病变在观察期内（照后6月）仍未见恢复,照射后动物眼底动静脉和毛细血管稍有扩张充血,但未见瘢痕、裂隙、出血等表现。结论：实验所用剂量范围内的HPM重复照射可以对动物角膜、晶状体、玻璃体等部位造成一定程度的生物效应,并呈现出一定的量效关系;在实验的观察期内,角膜和眼底依照射剂量不同可分别于照后不同期间恢复正常,但晶状体混浊在观察期末仍未见恢复,能否发展成微波白内障尚需观察。     

Focusing by shape change in the lens of the eye: a commentary on Young (1801) ‘On the mechanism of the eye’

In his Bakerian Lecture paper of 1801, Thomas Young provided the best account up to that time of the eye''s optical system, including refraction by the cornea and the surfaces of the lens. He built a device, an optometer, for determining the eye''s state of focus, making it possible to prescribe appropriate correction lenses. His main contribution, however, was to show that accommodation, the eye''s focusing mechanism, was not the result of changes to the curvature of the cornea, nor to the length of the eye, but was due entirely to changes in the shape of the lens, which he described with impressive accuracy. He was wrong, however, in believing that the reason the lens bulges when focusing on near objects was because it behaved as a contracting muscle. Half a century later, Helmholtz showed that the lens bulges not by its own contraction, but when it is relaxed as a result of contraction of newly discovered circular muscles in the ciliary body. This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society.     

Effects of aging in vitro on intracellular proteolysis in cultured rabbit lens epithelial cells in the presence and absence of serum

Summary Alterations in proteolytic capabilities have been associated with abnormalities in the aged eye lens, but in vivo tests of this hypothesis have been difficult to pursue. To simulate aging, we cultured cells from an 8-yr-old rabbit to early (population-doubling level 20 to 30) and late (population-doubling level > 125) passage. Long-lived (t_1/2>10 h) and short-lived (t_1/2<10 h) intracellular proteins were labeled with [³H]leucine, and the ability of the cells to mount a proteolytic response to the stress of serum withdrawal was determined. For early passage cells, the average t_1/2 of long-lived proteins in the presence and absence of serum was 62 and 39 h, respectively. For late-passage cells, the average t_1/2 of long-lived proteins in the presence and absence of serum was 58 and 43 h, respectively. The net increase in intracellular proteolysis in the absence of serum was 59 and 35% for early and late-passage cells, respectively. Thus, in vitro-aged rabbit lens epithelial cells mount only 60% the proteolytic response to serum removal shown in “younger” cells. The enhanced ability of early passage cells to respond to serum removal seems to involve lower homeostatic levels of proteolysis in the presence of serum and greater enhancement of proteolysis in the absence of serum. Less than 2% of the protein is in the pool of short-lived proteins. Rates of proteolysis of short-lived proteins in the presence and absence of serum were indistinguishable. With respect to basal proteolytic rates in the presence of serum and ability to mount a proteolytic response upon serum withdrawal, these rabbit lens epithelial cells are similar to bovine lens epithelial cells and fibroblasts. This work was supported in part by contract 53-3K06-5-10 U.S. Department of Agriculture, Washington, DC, Massachusetts Lions Eye Research FUnd, Inc., the Daniel and Florence Guggenheim Foundation, and a grant EY00362 from the National Eye Institute, Bethesda, MD.     

Vertebrate Crystallins--from Proteins to Genes

A review of literature on tissue-specific proteins of the vertebrate eye lens and genes coding for these proteins is presented. Particular attention is paid to the most heterogeneous family of crystallins: - and -crystallins, their nomenclature, and the structure of their genes. It is pointed out that mutations in gene coding for ubiquitous crystallins may be related to some forms of cataracts.     

Structural changes in alpha-crystallin and whole eye lens during heating, observed by low-angle X-ray diffraction

Whole eye lens and alpha-crystallin gels and solutions were investigated using X-ray scattering techniques at temperatures ranging from 20 degrees C to 70 degrees C. In whole lens isolated in phosphate-buffered saline, the spacing of the dominant X-ray reflection seen with low-angle scattering was constant from 20 degrees C to 45 degrees C but increased at 50 degrees C from 15.2 nm to 16.5 nm. At room temperature, the small-angle X-ray diffraction pattern of the intact lens was very similar to the pattern of alpha-crystallin gels at near-physiological concentration (approximately 300 mg/ml), so it is reasonable to assume that the alpha-crystallin pattern dominates the pattern of the intact lens. Our results therefore indicate that in whole lens alpha-crystallin is capable of maintaining its structural properties over a wide range of temperature. This property would be useful in providing protection for other lens proteins super-aggregating. In the alpha-crystallin gels, a moderate increase in both the spacing and intensity of the reflection was observed from 20 degrees C to 45 degrees C, followed by an accelerated increase from 45 degrees C to 70 degrees C. Upon cooling, this effect was found to be irreversible over 11 hours. Qualitatively similar results were observed for alpha-crystallin solutions at a variety of lower concentrations.     

Comparative electrophoretic studies of muscle and eye lens proteins in freshwater fish of Iraq

Muscle myogens and eye lens proteins have been studied in ten species of freshwater fish from Iraq. The electrophoretic analysis revealed that the muscle myogens can be considered as a good taxonomic criterion to differentiate the family Mugilidae from the Cyprinodontidae and Cyprinidae, but not between the families Poeciliidae and Cyprinodontidae. Within the Cyprinidae the muscle myogens can be used to diferentiate Barbus grypus from the remaining species of this family. Eye lens proteins are not considered a good taxonomic criterion to differentiate the members of the four families studied, but can distinguish B. belawayei and B. grypus from the other Cyprinid species.     

Fixed focal-length optics in pulmonate snails (Mollusca, Gastropoda): squaring phylogenetic background and ecophysiological needs (II)

Abstract. Our results suggest that freshwater pulmonates like Lymnaea stagnalis, Radix peregra, Physa fontinalis , and Planorbarius corneus have inherited from their terrestrial ancestors eyes with a spherical, immobile lens with fixed focal-length optics. Unable to change the dioptric apparatus to form an image under water, modifications to the retina had to occur if sharp vision was required. Computer-assisted calculations and 3-D eye reconstructions demonstrate that the photoreceptors in the deeper, ventral pit are in a position to perceive focused images under water. Vision in air, however, would favour photoreceptive cells located in the shallower, dorsal pit. On the basis of histological, ethological, and optical comparisons, we conclude that the eyes in L. stagnalis and R. peregra , species that are known to escape and seek temporary refuge above the water surface, are well adapted to function in water as well as air, but that the eyes in P. fontinalis and Pl. corneus are less modified from those of their terrestrial ancestors. We also conclude that good resolving power may be of greater importance in the aquatic pulmonates than the terrestrial species, since the former have to locate thin, vertical stems of reeds and sedges to ascend in order to reach the surface to breathe.     

CRE-decoy oligonucleotide-inhibition of gene expression and tumor growth

The authors prepared water-soluble (WSF), urea-soluble (USF), alkali-soluble (ASF), sonicated (SF), sonicated insoluble (SIF) and membrane (MF) fractions of lens proteins from human senile and diabetic cataractous lenses and age-matched clear lenses. Levels of advanced glycation end products (AGEs) including carboxymethyl lysine (CML), a glycoxidation product, were determined by both non-competitive and competitive enzyme-linked immunosorbent assay (ELISA). Distribution of AGEs in the various protein fractions was ascertained by SDS-PAGE and Western blotting. An overall increase in the levels of AGEs in diabetic cataractous lenses as compared to senile cataractous lenses and clear lenses has been observed. ASF and SF , both of which originated from the urea-insoluble fraction, showed the highest levels of AGEs. However, no clear-cut differences in CML levels were seen among clear lenses and senile and diabetic cataractous lenses. AGEs were found to be distributed mostly in the high molecular aggregates in all the fractions. These data suggest that AGEs contribute to protein aggregation and subsequent insolubilization.     

High-resolution X-ray crystal structures of human gammaD crystallin (1.25 A) and the R58H mutant (1.15 A) associated with aculeiform cataract

Several human cataracts have been linked to mutations in the gamma crystallin gene. One of these is the aculeiform cataract, which is caused by an R58H mutation in gammaD crystallin. We have shown previously that this cataract is caused by crystallization of the mutant protein, which is an order of magnitude less soluble than the wild-type. Here, we report the very high-resolution crystal structures of the mutant and wild-type proteins. Both proteins crystallize in the same space group and lattice. Thus, a strict comparison of the protein-protein and protein-water intermolecular interactions in the two crystal lattices is possible. Overall, the differences between the mutant and wild-type structures are small. At position 58, the mutant protein loses the direct ion-pair intermolecular interaction present in the wild-type, due to the differences between histidine and arginine at the atomic level; the interaction in the mutant is mediated by water molecules. Away from the mutation site, the mutant and wild-type lattice structures differ in the identity of side-chains that occupy alternate conformations. Since the interactions in the crystal phase are very similar for the two proteins, we conclude that the reduction in the solubility of the mutant is mainly due to the effect of the R58H mutation in the solution phase. The results presented here are also important as they are the first high-resolution X-ray structures of human gamma crystallins.     

Biological glass: structural determinants of eye lens transparency

The purpose of the lens is to project a sharply focused, undistorted image of the visual surround onto the neural retina. The first pre-requisite, therefore, is that the tissue should be transparent. Despite the presence of remarkably high levels of protein, the lens cytosol remains transparent as a result of short-range-order interactions between the proteins. At a cellular level, the programmed elimination of nuclei and other light-scattering organelles from cells located within the pupillary space contributes directly to tissue transparency. Scattering at the cell borders is minimized by the close apposition of lens fibre cells facilitated by a plethora of adhesive proteins, some expressed only in the lens. Similarly, refractive index matching between lens membranes and cytosol is believed to minimize scatter. Refractive index matching between the cytoplasm of adjacent cells is achieved through the formation of cellular fusions that allow the intermingling of proteins. Together, these structural adaptations serve to minimize light scatter and enable this living, cellular structure to function as 'biological glass'.