Thermal and Spectral Sensitivities of Discrete Slow Potentials in Limulus Eye

The discrete, subthreshold, slow potential fluctuations (SPF's) which can be recorded intracellularly in Limulus ommatidia are sensitive to temperature and light wavelength. SPF frequency increases with increasing temperature (Q₁₀ about 3.5) and light intensity. The effects are additive. SPF rise and decay time decrease with increasing temperature (Q₁₀ between 2 and 3). There is a peak, near 520 nm, in the spectral sensitivity of SPF frequency. This peak may correspond to the wavelength of maximum absorption by rhodopsin in the ommatidia. Hydroxylamine produces a rapid, irreversible reduction of SPF frequency and amplitude perhaps owing to its action on the photopigment. The cornea and crystalline cones fluoresce (peak about 445 nm) when excited by near-ultraviolet energy (380 nm peak) and this fluorescence may influence SPF spectral sensitivity measurements. These findings suggest that the SPF's are the results of photolytic and thermolytic reactions occurring in the ommatidial visual pigments and that they have a role in the mechanisms which transduce light to electrical activity in the visual receptors.     

Fixational Eye Movement Correction of Blink-Induced Gaze Position Errors

Our eyes move continuously. Even when we attempt to fix our gaze, we produce “fixational” eye movements including microsaccades, drift and tremor. The potential role of microsaccades versus drifts in the control of eye position has been debated for decades and remains in question today. Here we set out to determine the corrective functions of microsaccades and drifts on gaze-position errors due to blinks in non-human primates (Macaca mulatta) and humans. Our results show that blinks contribute to the instability of gaze during fixation, and that microsaccades, but not drifts, correct fixation errors introduced by blinks. These findings provide new insights about eye position control during fixation, and indicate a more general role of microsaccades in fixation correction than thought previously.     

sox4 And sox11 Function during Xenopus laevis Eye Development

SoxC genes are involved in many developmental processes such as cardiac, lymphoid, and bone development. The SoxC gene family is represented by Sox4, Sox11, and Sox12. Loss of either Sox4 or Sox11 function is lethal during mouse embryogenesis. Here, we demonstrate that sox4 and sox11 are strongly expressed in the developing eye, heart as well as brain in Xenopus laevis. Morpholino oligonucleotide mediated knock-down approaches in anterior neural tissue revealed that interference with either Sox4 or Sox11 function affects eye development. A detailed analysis demonstrated strong effects on eye size and retinal lamination. Neural induction was unaffected upon Sox4 or Sox11 MO injection and early eye field differentiation and cell proliferation were only mildly affected. Depletion of both genes, however, led independently to a significant increase in cell apoptosis in the eye. In summary, Sox4 and Sox11 are required for Xenopus visual system development.     

Slow Replication Fork Velocity of Homologous Recombination-Defective Cells Results from Endogenous Oxidative Stress

Replications forks are routinely hindered by different endogenous stresses. Because homologous recombination plays a pivotal role in the reactivation of arrested replication forks, defects in homologous recombination reveal the initial endogenous stress(es). Homologous recombination-defective cells consistently exhibit a spontaneously reduced replication speed, leading to mitotic extra centrosomes. Here, we identify oxidative stress as a major endogenous source of replication speed deceleration in homologous recombination-defective cells. The treatment of homologous recombination-defective cells with the antioxidant N-acetyl-cysteine or the maintenance of the cells at low O₂ levels (3%) rescues both the replication fork speed, as monitored by single-molecule analysis (molecular combing), and the associated mitotic extra centrosome frequency. Reciprocally, the exposure of wild-type cells to H₂O₂ reduces the replication fork speed and generates mitotic extra centrosomes. Supplying deoxynucleotide precursors to H₂O₂-exposed cells rescued the replication speed. Remarkably, treatment with N-acetyl-cysteine strongly expanded the nucleotide pool, accounting for the replication speed rescue. Remarkably, homologous recombination-defective cells exhibit a high level of endogenous reactive oxygen species. Consistently, homologous recombination-defective cells accumulate spontaneous γH2AX or XRCC1 foci that are abolished by treatment with N-acetyl-cysteine or maintenance at 3% O₂. Finally, oxidative stress stimulated homologous recombination, which is suppressed by supplying deoxynucleotide precursors. Therefore, the cellular redox status strongly impacts genome duplication and transmission. Oxidative stress should generate replication stress through different mechanisms, including DNA damage and nucleotide pool imbalance. These data highlight the intricacy of endogenous replication and oxidative stresses, which are both evoked during tumorigenesis and senescence initiation, and emphasize the importance of homologous recombination as a barrier against spontaneous genetic instability triggered by the endogenous oxidative/replication stress axis.     

早期胚胎发育母源基因的表达调控

精卵细胞是自身细胞系谱发生的产物 ,具有与双亲生物环境相互作用发育的先天性遗传。受精是新个体发育的起始点 ,是基因表达在胚胎发育过程中的选择性和时间上的规律顺序[1,2 ] 。基因组内各个基因表达的选择性和程度 ,无论是由单基因的突变引起或是多基因的复杂影响引起 ,都随时间、位置和环境条件的不同而发生改变[3 ] 。基因表达的变化是控制个体发生的细调节中心 ,决定着所有的生命过程。1 .早期胚胎发育的物质基础伴随卵母细胞生长的是核糖体和信使ＲＮＡｓ转录活化 ,Ｐｏｌｙ(Ａ)ｍＲＮＡ的合成约占总ＲＮＡ的 2 0 % ,小鼠大约在排卵…     

A Screen for Genes That Function Downstream of Ras1 during Drosophila Eye Development

Cell-fate specification of the R7 photoreceptor cell is controlled by the sevenless receptor tyrosine kinase (SevRTK) and Ras1, the Drosophila homologue of mammalian H-ras, K-ras and N-ras oncogenes. An activated form of Ras1 expressed under control of the sevenless enhancer/promoter (sev-Ras1(V12)) induces production of supernumerary R7 photoreceptor cells, which causes the eye to become rough in appearance. To isolate mutations in genes functioning downstream of Ras1, we carried out a screen for dominant suppressors and enhancers of this rough eye phenotype. Approximately 850,000 mutagenized flies were screened, and 282 dominant suppressors and 577 dominant enhancers were isolated. Mutations in the Drosophila homologues of Raf, MEK, MAPK, type I Geranylgeranyl Transferase and Protein Phosphatase 2A were isolated, as were mutations in several novel signaling genes. Some of these mutant genes appear to be general signaling factors that function in other Ras1 pathways, while one seems to be more specific for photoreceptor development. At least two suppressors appear to function either between Ras1 and Raf or in parallele to Raf.     

Analysis of Slow Hyperpolarizing Potentials in Frog Taste Cells Induced by Glossopharyngeal Nerve Stimulation

Chemical Senses, 29,     

Contracture of Slow Striated Muscle during Calcium Deprivation

When deprived of calcium the slow striated muscle fibers of the frog develop reversible contractures in either hypertonic or isotonic solutions. While calcium deprivation continues because of a flowing calcium-free solution the muscles relax slowly and completely. Restoration of calcium during contracture relaxes the muscle promptly to initial tension. When relaxed during calcium lack the return of calcium does not change tension and the muscle stays relaxed. When contractures are induced by solutions containing small amounts of calcium relaxation does not occur or requires several hours. The rate of tension development depends upon the rate at which calcium moves outward since the contractures develop slower in low concentrations of calcium and are absent or greatly slowed in a stagnant calcium-free solution. Withdrawal of calcium prevents the contractile responses to ACh, KCl, or electrical stimulation through the nerve. Muscles return to their original excitability after calcium is restored. Origin of the contractures is unrelated to nerve activity since they are maximal during transmission failure from calcium lack, occur in denervated muscles, and are not blocked by high concentrations of d-tubocurarine, procaine, or atropine. The experiments also indicate that the contractures do not originate from repetitive activity of muscle membranes. The findings are most simply explained by relating the outward movement of calcium as a link for initiating contraction in slow type striated muscle.     

新型深部脑刺激模式的开发及研究进展

深部脑刺激(deep brain stimulation,DBS)已成为治疗帕金森病等运动障碍疾病的常规方法之一,并且在许多其他神经和精神疾病的治疗中也具有良好的应用前景.但是,目前常规DBS采用单通道恒定脉冲间隔的高频刺激(high frequency stimulation,HFS),刺激模式缺少多样化,限制了DBS在临床上的推广应用.为了开发更多DBS刺激模式,用于改善疗效、拓展应用范围、并节省刺激器的电能,近年来研究人员基于去同步调控机制,在脉冲序列的时间模式和空间排布两方面开发了DBS新模式.主要包括:变频序列(包括规则变频和随机变频)、不同空间位点上的多通道异步刺激以及变频和多通道两者的结合.这些新刺激模式能够提高DBS的临床疗效、降低刺激能耗,在帕金森病以及癫痫、强迫症和微意识障碍等其他脑疾病的治疗中都展现了良好的应用前景.更值得关注的是,多通道异步刺激不仅在刺激期间具有更好的即时疗效,而且刺激结束后还能长时间保持疗效,具有刺激后效应.这个特性突破了常规DBS主要为即时效应的局限性,展现了DBS新前景.本文在概述常规DBS模式及其去同步调控机制的基础上,综述变频脉冲刺激和...     

Slow recovery of body fat lost during adenovirus-induced hyperleptinemia

In normal rats, adenovirus-induced hyperleptinemia causes disappearance of visible body fat, downregulation of lipogenic enzymes, and upregulation of oxidative enzymes and thermogenic proteins. In addition, preadipocyte markers replace mature adipocyte markers, suggesting dedifferentiation. In weight loss induced by caloric restriction, by contrast, the lipogenic machinery is essentially intact. To determine if the radical changes induced by leptin would slow the reappearance of body fat, we compared normal lean rats made hyperleptinemic by infusing an adenovirus-leptin construct with diet-matched littermates. Initially, in plasma leptin the hyperleptinemic rats averaged approximately 50x the controls and, although it declined progressively, it was still slightly elevated at 150 days (P < 0.05). In the hyperleptinemics, body fat mass, quantified by magnetic resonance spectroscopy, remained below the pretreatment value for 60 days, while in diet-matched controls it exceeded the pretreatment value. Epididymal fat pad weight in hyperleptinemics was still 28% below paired controls at 150 days posttreatment. Histologic examination revealed adipocytes of hyperleptinemic animals to be smaller 60 days after treatment. At 60 days, adipose tissue UCP-2 gene expression in hyperleptinemics was still above controls, but expression of other lipogenic and oxidative enzymes had returned to baseline expression levels. We conclude that in normal rats recovery of body fat following adenovirus-induced hyperleptinemia is much slower than after caloric restriction, possibly because of persistent upregulation of adipocyte UCP-2.     

Eye Movements Reveal Effects of Visual Content on Eye Guidance and Lexical Access during Reading

Background

Normal reading requires eye guidance and activation of lexical representations so that words in text can be identified accurately. However, little is known about how the visual content of text supports eye guidance and lexical activation, and thereby enables normal reading to take place.

Methods and Findings

To investigate this issue, we investigated eye movement performance when reading sentences displayed as normal and when the spatial frequency content of text was filtered to contain just one of 5 types of visual content: very coarse, coarse, medium, fine, and very fine. The effect of each type of visual content specifically on lexical activation was assessed using a target word of either high or low lexical frequency embedded in each sentence

Results

No type of visual content produced normal eye movement performance but eye movement performance was closest to normal for medium and fine visual content. However, effects of lexical frequency emerged early in the eye movement record for coarse, medium, fine, and very fine visual content, and were observed in total reading times for target words for all types of visual content.

Conclusion

These findings suggest that while the orchestration of multiple scales of visual content is required for normal eye-guidance during reading, a broad range of visual content can activate processes of word identification independently. Implications for understanding the role of visual content in reading are discussed.     

Prdm8 Regulates the Morphological Transition at Multipolar Phase during Neocortical Development

Here, we found that the PR domain protein Prdm8 serves as a key regulator of the length of the multipolar phase by controlling the timing of morphological transition. We used a mouse line with expression of Prdm8-mVenus reporter and found that Prdm8 is predominantly expressed in the middle and upper intermediate zone during both the late and terminal multipolar phases. Prdm8 expression was almost coincident with Unc5D expression, a marker for the late multipolar phase, although the expression of Unc5D was found to be gradually down-regulated to the point at which mVenus expression was gradually up-regulated. This expression pattern suggests the possible involvement of Prdm8 in the control of the late and terminal multipolar phases, which controls the timing for morphological transition. To test this hypothesis, we performed gain- and loss-of-function analysis of neocortical development by using in utero electroporation. We found that the knockdown of Prdm8 results in premature change from multipolar to bipolar morphology, whereas the overexpression of Prdm8 maintained the multipolar morphology. Additionally, the postnatal analysis showed that the Prdm8 knockdown stimulated the number of early born neurons, and differentiated neurons located more deeply in the neocortex, however, majority of those cells could not acquire molecular features consistent with laminar location. Furthermore, we found the candidate genes that were predominantly utilized in both the late and terminal multipolar phases, and these candidate genes included those encoding for guidance molecules. In addition, we also found that the expression level of these guidance molecules was inhibited by the introduction of the Prdm8 expression vector. These results indicate that the Prdm8-mediated regulation of morphological changes that normally occur during the late and terminal multipolar phases plays an important role in neocortical development.     

Stimulation of lipid-linked oligosaccharide assembly during oviduct differentiation

Regulation of dolichyl phosphate-linked oligosaccharide assembly has been studied during the course of diethylstilbestrol-induced chick oviduct differentiation. Oviduct membranes from treated chicks form 4.6 times as much GlcNAc-P-P-Dol and GlcNAc2-P-P-Dol upon incubation with UDP-[14C]GlcNAc and MgCl2 than do membranes from untreated chicks. Assembly of oligosaccharide-lipid was studied by incubation of membranes with purified exogenous [14C]GlcNAc2-P-P-Dol and GDP-Man. Man transfer required a divalent cation (10 mM Mg2+) and detergent (0.5% Nonidet P-40 is optimal) and occurs in the presence of amphomycin (500 micrograms/ml). The apparent Km for GDP-Man is 1 microM and for [14C]GlcNAc2-P-P-Dol is 0.45 microM. The products are a series of sequentially formed dolichyl pyrophosphate-linked saccharides up to Man5GlcNAc2, the first of which is Man beta 1,4GlcNAc2. The same products are formed either in the presence or absence of amphomycin. Conversion of GlcNAc2-P-P-Dol to higher oligosaccharides is stimulated 3-fold by estrogen treatment of chicks. Similarly, the conversion of partially purified exogenously added Man beta-[14C]GlcNAc2-P-P-Dol is 4.6-fold higher after diethylstilbestrol treatment.     

Developmental Regulation of Nucleolus Size during Drosophila Eye Differentiation

When cell cycle withdrawal accompanies terminal differentiation, biosynthesis and cellular growth are likely to change also. In this study, nucleolus size was monitored during cell fate specification in the Drosophila eye imaginal disc using fibrillarin antibody labeling. Nucleolus size is an indicator of ribosome biogenesis and can correlate with cellular growth rate. Nucleolar size was reduced significantly during cell fate specification and differentiation, predominantly as eye disc cells entered a cell cycle arrest that preceded cell fate specification. This reduction in nucleolus size required Dpp and Hh signaling. A transient enlargement of the nucleolus accompanied cell division in the Second Mitotic Wave. Nucleoli continued to diminish in postmitotic cells following fate specification. These results suggest that cellular growth is regulated early in the transition from proliferating progenitor cells to terminal cell fate specification, contemporary with regulation of the cell cycle, and requiring the same extracellular signals.     

Slow Oscillations of the Purkinje Cell Firing Rate Induced by Electrical Stimulation of the Locus Coeruleus in Rats

In anesthetized Wistar rats, we studied the effect of electrical stimulation of the locus coeruleus (LC) on the firing rates of Purkinje cells using spectral analysis. The frequency of extracellularly recorded activity of Purkinje cells was measured before and during the 1st, 5th, 6th, and 11th min after cessation of 10-sec-long LC stimulations. Spectral analysis of the Purkinje cell firing rates (imp./bin, the bin duration was 2^-8 sec) for 60- to 120-sec-long intervals was performed using fast Fourier transformation after digital conversion of unitary spikes. Mean power spectra of the Purkinje cell firing rates (derived from 8-sec-long consecutive epochs at a sampling rate of 256 sec^-1) showed an increase in the slow frequency range (0.1-1.0 Hz) after LC stimulation, particularly due to the slowest components (below 0.5 Hz). This effect lasted more than 1 min and usually less than 6 min after cessation of LC stimulation and could be interpreted as the development of slow oscillations in the Purkinje cell firing. Our results suggest that slow oscillations of the firing rate of cerebellar output neurons, induced by LC stimulation, reflect a specific coordination of the cerebellar neuronal activities (important for a central norepinephrine influence) in regulation of different pathological states.     

A Kinetic Characterization of Slow Inactivation of Ribulosebisphosphate Carboxylase during Catalysis

The catalytic activity of ribulosebisphosphate carboxylase (Rubisco) declined as soon as catalysis was initiated by exposure to its substrate, d-ribulose-1,5-bisphosphate (ribulose-P(2)). The decline continued exponentially, with a half-time of approximately 7 minutes until, eventually, a steady state level of activity was reached which could be as low as 15% of the initial activity. The ratio of the steady state activity to the initial activity was lower at low CO(2) concentration and at low pH. The inhibitors 6-phosphogluconate and H(2)O(2) alleviated the inactivation, increasing the final/initial rate ratio and the half-time. Varying ribulose-P(2) concentration in the range above that required to saturate catalysis did not affect the kinetics of inactivation. The affinities for CO(2) and ribulose-P(2) were unaffected by the inactivation. The decline in activity occurred with preparations of ribulose-P(2) which contained no detectable d-xylulose-1,5-bisphosphate and also with ribulose-P(2) which had been generated enzymatically immediately before use. Inclusion of an aldolase system for removing d-xylulose-1,5-bisphosphate also did not alter the inactivation process. The inactivated Rubisco did not recover after complete exhaustion of ribulose-P(2). We conclude that the inactivation is not caused by readily-reversible binding of ribulose-P(2) at a site different from the active site and that it is unlikely to be attributable to inhibitory contaminants in ribulose-P(2) preparations.