Effects of day-time exposure to different light intensities on light-induced melatonin suppression at night

Background

Bright nocturnal light has been known to suppress melatonin secretion. However, bright light exposure during the day-time might reduce light-induced melatonin suppression (LIMS) at night. The effective proportion of day-time light to night-time light is unclear; however, only a few studies on accurately controlling both day- and night-time conditions have been conducted. This study aims to evaluate the effect of different day-time light intensities on LIMS.

Methods

Twelve male subjects between the ages of 19 and 23 years (mean ± S.D., 20.8 ± 1.1) gave informed consent to participate in this study. They were exposed to various light conditions (<10, 100, 300, 900 and 2700 lx) between the hours of 09:00 and 12:00 (day-time light conditions). They were then exposed to bright light (300 lx) again between 01:00 and 02:30 (night-time light exposure). They provided saliva samples before (00:55) and after night-time light exposure (02:30).

Results

A one-tailed paired t test yielded significant decrements of melatonin concentration after night-time light exposure under day-time dim, 100- and 300-lx light conditions. No significant differences exist in melatonin concentration between pre- and post-night-time light exposure under day-time 900- and 2700-lx light conditions.

Conclusions

Present findings suggest the amount of light exposure needed to prevent LIMS caused by ordinary nocturnal light in individuals who have a general life rhythm (sleep/wake schedule). These findings may be useful in implementing artificial light environments for humans in, for example, hospitals and underground shopping malls.     

Design and Construction of an Inexpensive Homemade Plant Growth Chamber

Plant growth chambers produce controlled environments, which are crucial in making reproducible observations in experimental plant biology research. Commercial plant growth chambers can provide precise controls of environmental parameters, such as temperature, humidity, and light cycle, and the capability via complex programming to regulate these environmental parameters. But they are expensive. The high cost of maintaining a controlled growth environment is often a limiting factor when determining experiment size and feasibility. To overcome the limitation of commercial growth chambers, we designed and constructed an inexpensive plant growth chamber with consumer products for a material cost of $2,300. For a comparable growth space, a commercial plant growth chamber could cost $40,000 or more. Our plant growth chamber had outside dimensions of 1.5 m (W) x 1.8 m (D) x 2 m (H), providing a total growth area of 4.5 m² with 40-cm high clearance. The dimensions of the growth area and height can be flexibly changed. Fluorescent lights with large reflectors provided a relatively spatially uniform photosynthetically active radiation intensity of 140–250 μmoles/m²/sec. A portable air conditioner provided an ample cooling capacity, and a cooling water mister acted as a powerful humidifier. Temperature, relative humidity, and light cycle inside the chamber were controlled via a z-wave home automation system, which allowed the environmental parameters to be monitored and programmed through the internet. In our setting, the temperature was tightly controlled: 22.2°C±0.8°C. The one-hour average relative humidity was maintained at 75%±7% with short spikes up to ±15%. Using the interaction between Arabidopsis and one of its bacterial pathogens as a test experimental system, we demonstrate that experimental results produced in our chamber were highly comparable to those obtained in a commercial growth chamber. In summary, our design of an inexpensive plant growth chamber will tremendously increase research opportunities in experimental plant biology.     

Size Scaling of Microtubule Assemblies in Early Xenopus Embryos

The first 12 cleavage divisions in Xenopus embryos provide a natural experiment in size scaling, as cell radius decreases ∼16-fold with little change in biochemistry. Analyzing both natural cleavage and egg extract partitioned into droplets revealed that mitotic spindle size scales with cell size, with an upper limit in very large cells. We discuss spindle-size scaling in the small- and large-cell regimes with a focus on the “limiting-component” hypotheses. Zygotes and early blastomeres show a scaling mismatch between spindle and cell size. This problem is solved, we argue, by interphase asters that act to position the spindle and transport chromosomes to the center of daughter cells. These tasks are executed by the spindle in smaller cells. We end by discussing possible mechanisms that limit mitotic aster size and promote interphase aster growth to cell-spanning dimensions.How components and processes within cells scale in size and rate with the size of the cell has become a topic of considerable interest in recent years (reviewed in Chan and Marshall 2012; Goehring and Hyman 2012; Levy and Heald 2012). For molecular machines with precise architectures (e.g., ribosomes), size is invariant, but rates of assembly and function, which depend on regulation and energy, might scale. For assemblies whose dimensions are not hard wired (e.g., cytoskeleton assemblies and organelles), both size and rate might scale. For pathways involving distributed biochemical change (e.g., the cell-cycle oscillator), size is not well defined, but rate might scale in interesting ways. Here, we will address only size scaling, and refer the reader to interesting recent progress on cell-cycle timing in early Xenopus embryos (Chang and Ferrell 2013; Tsai et al. 2014).Size-scaling relationships, which are part of the science of allometry, have long informed on whole organism physiology. Explicitly seeking them at the subcellular level is a newer endeavor, which in our mind holds two kinds of promise. It can inform on mechanism at the level of integrated cell physiology (e.g., on establishment of cleavage plane geometry). It can also inform on molecular processes involved in assembly growth and dynamics, and perhaps help us discern logic in often frustratingly complex molecular architectures. It is not obvious, for example, why ∼100 protein complexes are required to build a mitotic spindle in higher eukaryotes (Hutchins et al. 2010), when bacteria can segregate plasmids with far fewer (Salje et al. 2010). Part of the answer is the need for higher fidelity in the eukaryotic process. Gerhart and Kirschner (1997) also emphasized the need for highly adaptable processes in the evolution of higher eukaryotes. At least part of the complexity of subcellular assemblies might reflect the need for adaptable scaling of size, shape, and timing.Vertebrate embryos derived from large eggs provide a natural experiment in size scaling (Fig. 1). A Xenopus laevis egg, for example, is ∼1.2 mm in diameter. Following fertilization, it cleaves completely ∼12 times at an approximately constant rate of ∼2 divisions/h (most rates in early development are temperature dependent, and can vary up to about eightfold over the tolerated range). These divisions generate a quasispherical array of quasispherical cells that are, on average, smaller by 2¹²-fold in volume, or 2⁴-fold in radius. The first 12 divisions occur with little gene expression and little change in cell physiology, and it may be reasonable to assume approximately constant biochemistry (discussed below), other than periodic cell-cycle regulation. After the 12th division, cell physiology changes dramatically as part of the midblastula transition (MBT) (discussed below), which provides a natural cut-off for size-scaling investigations. An interesting and potentially informative complication is that cleaving amphibian embryos develop a gradient in blastomere sizes, with larger cells at the vegetal pole where yolk is more abundant (evident in Fig. 1C,D). Larger blastomeres tend to divide more slowly, which gradually eliminates division synchrony (Gerhart 1980).Open in a separate windowFigure 1.Spindle-size scaling in Xenopus laevis. A–D show confocal images of eggs and early embryos fixed at different stages, stained for tubulin (red) and DNA (green), cleared and imaged by confocal microscopy. Embryos containing metaphase spindles were selected for analysis. (A) Unfertilized egg with meiosis-II spindle (blue arrow). (B) First mitosis. Note scaling mismatch between the spindle and egg. (C,D) Cleavage stages. (E) Spindle lengths and cell lengths derived from confocal images like A–D. Note spindle length is approximately constant in the large-cell regime and scales with cell size in the small-cell regime. (F) Spindle assembled in a droplet of unfertilized egg extract containing fluorescent probes suspended in oil and imaged live. aNuMA, anti-nuclear mitotic apparatus. (A–E from Wühr et al. 2008; adapted, with permission, from the author; F is an unpublished image provided by Jesse Gatlin, University of Wyoming, which is similar to images in Hazel et al. 2013.)Embryos from different species have pros and cons for experimental analysis of size scaling during early divisions. Amphibian eggs provide a large dynamic range in cell size, complete division, and quasispherical geometry of both cells and embryos. In the minus column, they are opaque unless fixed and cleared and difficult to manipulate using genetics. Undiluted, cell-free extracts from Xenopus eggs and early embryos provide access to live imaging and molecular analysis and recapitulate the biology of intact eggs, including scaling relationships (Wilbur and Heald 2013), but it is important to go back to the intact embryo to check validity of key findings where possible. Zebrafish eggs provide a transparent, genetically tractable vertebrate system with very large cells but incomplete cleavage at early stages. Caenorhabditis elegans and Drosophila embryos have excellent imaging and genetics, which are advantages for scaling analysis, especially rate scaling (e.g., Carvalho et al. 2009; Hara and Kimura 2013), but these embryos start smaller, so they provide a lower dynamic range for analyzing size-scaling behavior.     

Cytoprotective Effects of Grape Seed Extract on Human Gingival Fibroblasts in Relation to Its Antioxidant Potential

Cytoprotective effects of short-term treatment with grape seed extract (GSE) upon human gingival fibroblasts (hGFs) were evaluated in relation to its antioxidant properties and compared with those of a water-soluble analog of vitamin E: trolox (Tx). GSE and Tx showed comparable antioxidant potential in vitro against di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium (DPPH; a stable radical), hydroxyl radical (^•OH), singlet oxygen (¹O₂), and hydrogen peroxide (H₂O₂). Pretreatment or concomitant treatment with GSE for 1 min protected hGFs from oxidative stressors, including H₂O₂, acid-electrolyzed water (AEW), and ¹O₂, and attenuated the intracellular formation of reactive oxygen species induced by H₂O₂ and AEW. Tx also reduced the H₂O₂- and AEW-induced intracellular formation of reactive oxygen species, but showed no cytoprotective effects on hGFs exposed to H₂O₂, AEW, or ¹O₂. These results suggest that the cytoprotective effects of GSE are likely exerted independently of its antioxidant potential.     

Substrate selectivity of epidermal growth factor-receptor ligand sheddases and their regulation by phorbol esters and calcium influx

Signaling via the epidermal growth factor receptor (EGFR), which has critical roles in development and diseases such as cancer, is regulated by proteolytic shedding of its membrane-tethered ligands. Sheddases for EGFR-ligands are therefore key signaling switches in the EGFR pathway. Here, we determined which ADAMs (a disintegrin and metalloprotease) can shed various EGFR-ligands, and we analyzed the regulation of EGFR-ligand shedding by two commonly used stimuli, phorbol esters and calcium influx. Phorbol esters predominantly activate ADAM17, thereby triggering a burst of shedding of EGFR-ligands from a late secretory pathway compartment. Calcium influx stimulates ADAM10, requiring its cytoplasmic domain. However, calcium influx-stimulated shedding of transforming growth factor alpha and amphiregulin does not require ADAM17, even though ADAM17 is essential for phorbol ester-stimulated shedding of these EGFR-ligands. This study provides new insight into the machinery responsible for EGFR-ligand release and thus EGFR signaling and demonstrates that dysregulated EGFR-ligand shedding may be caused by increased expression of constitutively active sheddases or activation of different sheddases by distinct stimuli.     

Platinum nanoparticle is a useful scavenger of superoxide anion and hydrogen peroxide

Bimetallic nanoparticles consisting of gold and platinum were prepared by a citrate reduction method and complementarily stabilized with pectin (CP-Au/Pt). The percent mole ratio of platinum was varied from 0 to 100%. The CP-Au/Pt were alloy-structured. They were well dispersed in water. The average diameter of platinum nanoparticles (CP-Pt) was 4.7 +/- 1.5 nm. Hydrogen peroxide (H(2)O(2)) was quenched by CP-Au/Pt consisting of more than 50% platinum whereas superoxide anion radical (O(2)(-)) was quenched by any CP-Au/Pt. The CP-Au/Pt quenched these two reactive oxygen species in dose-dependent manners. The CP-Pt is the strongest quencher. The CP-Pt decomposed H(2)O(2) and consequently generated O(2) like catalase. The CP-Pt actually quenched O(2)(-) which was verified by a superoxide dismutase (SOD) assay kit. This quenching activity against O(2)(-) persisted like SOD. Taken together, CP-Pt may be a SOD/catalase mimetic which is useful for medical treatment of oxidative stress diseases.     

Study on roles of anaplerotic pathways in glutamate overproduction of <Emphasis Type="Italic">Corynebacterium glutamicum</Emphasis> by metabolic flux analysis

Background  

Corynebacterium glutamicum has several anaplerotic pathways (anaplerosis), which are essential for the productions of amino acids, such as lysine and glutamate. It is still not clear how flux changes in anaplerotic pathways happen when glutamate production is induced by triggers, such as biotin depletion and the addition of the detergent material, Tween 40. In this study, we quantitatively analyzed which anaplerotic pathway flux most markedly changes the glutamate overproduction induced by Tween 40 addition.