Recovery of photosynthesis and phtosystem II fluorescence in Chlamydomonas reinhardtii after exposure to three levels of high light

Recovery from 60 min of photoinhibitory treatment at photosynthetic photon flux densities of 500, 1400 and 2200 μMmol m^?2 s^? was followed in cells of the green alga Chlamydomonas reinhardtii grown at 125 μMmol m^?2 s^?1. These light treatments represent photoregulation, moderate photoinhibition and strong photoinhibition, respectively. Treatment in photoregulatory light resulted in an increased maximal rate of oxygen evolution (P_max) and an increased quantum yield (Φ), but a 15% decrease in F_v/F_M. Treatment at moderately photoinhibitory light resulted in a 30% decrease in F_v/F_M and an approximately equal decrease in Φ. Recovery in dim light restored F_v/F_M within 15 and 45 min after high light treatment at 500 and 1400 μMmol m^?2 s^?1, respectively. Convexity (Θ), a measure of the extent of co-limitation between PS II turnover and whole-chain electron transport, and Φ approached, but did not reach the control level during recovery after exposure to 1400 μMmol m^?2 s^?1, whereas P_max increased above the control. Treatment at 2200 μMmol m^?2 s^?1 resulted in a strong reduction of the modeled parameters Φ, Θ and P_max. Subsequent recovery was initially rapid but the rate decreased, and a complete recovery was not reached within 120 min. Based on the results, it is hypothesized that exposure to high light results in two phenomena. The first, expressed at all three light intensities, involves redistribution within the different aspects of PS II heterogeneity rather than a photoinhibitory destruction of PS II reaction centers. The second, most strongly expressed at 2200 μmol m^?2 s^?1, is a physical damage to PS II shown as an almost total loss of PS II_α and PS II Q_B-reducing centers. Thus recovery displayed two phase, the first was rapid and the only visible phase in algae exposed to 500 and 1400 μmol m^?2 s^?1. The second phase was slow and visible only in the later part of recovery in cells exposed to 2200 μmol m^?2 s^?1.     

Redox Properties Of Phenols, Their Relationships To Singlet Oxygen Quenching And To Their Inhibitory Effects On Benzo(A)Pyrene-Induced Neoplasia

The inhibitory effects of synthetic phenolic compounds on benzo(a)pyrene-induced neoplasia of the mouse forestomach have been measured by Wattenberg et al⁶ The efficiency of this inhibition has been estimated for each phenol, using R, the ratio of the number of tumors per mouse in the protected group over the number of tumours per mouse in the control group. We have observed a linear correlation between the chemoprotection efficiency R and the logarithm of the rate of quenching of singlet oxygen. k. by this family of phenols, log k being itself correlated with the one-electron oxidation potential of the phenols. These correlations suggest a charge transfer mechanism for the inhibition of neoplasia induced hy benzo(a)py-rene. The correlations described provide a theoretical basis for scaling the inhibitors of mutagenicity induced by polycyclic aromatic compounds in terms of their oxidation potentials     

低氧对胚胎干细胞增殖的影响

目的:观察间歇性低氧和持续性低氧对体外培养的胚胎干细胞(ES细胞)增殖的影响.方法:利用细胞记数法和BrdU (5-溴脱氧尿苷)掺入的流式细胞分析检测细胞增殖,并用RT -PCR的方法检测低氧诱导因子(HIF-1a)的表达变化.结果:①将ES细胞分别放在低氧(3%～10% O2)和常氧(20% O2)的环境中培养24 h后,在低氧环境中培养的ES细胞数较常氧组明显减少;②将ES细胞分别给予间歇性低氧刺激(3%～10% O2),每天10 min,连续4 d后,发现3%低氧组较常氧对照组的细胞增殖明显升高.③用RT-PCR方法观察HIF-1a的表达与细胞增殖的关系,发现在常氧环境中培养的ES即有HIF-1a的表达,ES细胞在持续低氧24 h或间歇性低氧(3%～10% O2)刺激4 d后对HIF-1a的表达均无明显影响.结论:间歇性低氧(3% O2)可明显促进体外培养的ES细胞增殖,而持续性低氧抑制ES细胞增殖,间歇性低氧(3% O2)刺激促进ES细胞增殖的机制尚有待于进一步的研究.     

Micro(mi) RNA-34a targets protein phosphatase (PP)1γ to regulate DNA damage tolerance

The DNA damage response (DDR) triggers widespread changes in gene expression, mediated partly by alterations in micro(mi) RNA levels, whose nature and significance remain uncertain. Here, we report that miR-34a, which is upregulated during the DDR, modulates the expression of protein phosphatase 1γ (PP1γ) to regulate cellular tolerance to DNA damage. Multiple bio-informatic algorithms predict that miR-34a targets the PP1CCC gene encoding PP1γ protein. Ionising radiation (IR) decreases cellular expression of PP1γ in a dose-dependent manner. An miR-34a-mimic reduces cellular PP1γ protein. Conversely, an miR-34a inhibitor antagonizes IR-induced decreases in PP1γ protein expression. A wild-type (but not mutant) miR-34a seed match sequence from the 3′ untranslated region (UTR) of PP1CCC when transplanted to a luciferase reporter gene makes it responsive to an miR-34a-mimic. Thus, miR-34a upregulation during the DDR targets the 3′ UTR of PP1CCC to decrease PP1γ protein expression. PP1γ is known to antagonize DDR signaling via the ataxia-telangiectasia-mutated (ATM) kinase. Interestingly, we find that cells exposed to DNA damage become more sensitive – in an miR-34a-dependent manner – to a second challenge with damage. Increased sensitivity to the second challenge is marked by enhanced phosphorylation of ATM and p53, increased γH2AX formation, and increased cell death. Increased sensitivity can be partly recapitulated by a miR-34a-mimic, or antagonized by an miR-34a-inhibitor. Thus, our findings suggest a model in which damage-induced miR-34a induction reduces PP1γ expression and enhances ATM signaling to decrease tolerance to repeated genotoxic challenges. This mechanism has implications for tumor suppression and the response of cancers to therapeutic radiation.     

IgE induces hypotension in asthma mice by down-regulating vascular NCX1 expression through activating MiR-212-5p

Immunoglobulin E (IgE) has been suggested as a risk factor for allergy-induced low blood pressure, which has not been well explained in molecular details. Our current study shows a novel mechanism involving IgE, Fc?R1, miRNA-212-5p (miR-212-5p), and sodium/calcium exchanger protein 1(NCX1) for asthma to induce hypotension. In arterial smooth muscle cells, IgE up-regulated miR212-5p via its receptor Fc?R1, which resulted in down-regulation of NCX1 that is a regulating factor for blood pressure. In mice, asthma induced hypotension by interfering vasoconstrictive function; knockout of Fc?R1 kept the asthmatic mice from developing hypotension; knock-down of miR-212-5p in asthmatic mice resulted in a significant restoration of blood pressure. In human, asthma and IgE were positively correlated with hypotension in cohort study on NIH epidemiological data. This study suggests a novel therapeutic target (miR-212-5p) for treatment of asthma-induced hypotension.     

A Cas12a-based CRISPR interference system for multigene regulation in mycobacteria

Mycobacteria are responsible for a heavy global disease burden, but their relative genetic intractability has long frustrated research efforts. The introduction of clustered regularly interspaced short palindromic repeats (CRISPR) interference (CRISPRi) has made gene repression in mycobacteria much more efficient, but limitations of the prototypical Cas9-based platform, for example, in multigene regulation, remain. Here, we introduce an alternative CRISPRi platform for mycobacteria that is based on the minimal type V Cas12a enzyme in combination with synthetic CRISPR arrays. This system is simple, tunable, reversible, can efficiently regulate essential genes and multiple genes simultaneously, and works as efficiently in infected macrophages as it does in vitro. Together, Cas12a-based CRISPRi provides a facile tool to probe higher-order genetic interactions in mycobacteria including Mycobacterium tuberculosis (Mtb), which will enable the development of synthetically lethal drug targets and the study of genes conditionally essential during infection.     

B(a)P暴露干扰细胞周期调控蛋白影响孕早期小鼠卵巢黄体功能

该研究旨在探讨苯并(a)芘[Benzo(a)pyrene,B(a)P]对孕早期小鼠卵巢黄体功能的影响及机制.体内模型:将昆明小鼠每晚按雌雄3∶1的比例合笼,次晨查得阴栓记为孕第1天(d1);将其随机分为对照组和B(a)P处理组,每日早晨称重后以0.1 mL/10 g动物体质量灌胃给予0.2 mg/(kg·d)的B(a)...     

A Microfluidic Platform for Precision Small-volume Sample Processing and Its Use to Size Separate Biological Particles with an Acoustic Microdevice

A major advantage of microfluidic devices is the ability to manipulate small sample volumes, thus reducing reagent waste and preserving precious sample. However, to achieve robust sample manipulation it is necessary to address device integration with the macroscale environment. To realize repeatable, sensitive particle separation with microfluidic devices, this protocol presents a complete automated and integrated microfluidic platform that enables precise processing of 0.15–1.5 ml samples using microfluidic devices. Important aspects of this system include modular device layout and robust fixtures resulting in reliable and flexible world to chip connections, and fully-automated fluid handling which accomplishes closed-loop sample collection, system cleaning and priming steps to ensure repeatable operation. Different microfluidic devices can be used interchangeably with this architecture. Here we incorporate an acoustofluidic device, detail its characterization, performance optimization, and demonstrate its use for size-separation of biological samples. By using real-time feedback during separation experiments, sample collection is optimized to conserve and concentrate sample. Although requiring the integration of multiple pieces of equipment, advantages of this architecture include the ability to process unknown samples with no additional system optimization, ease of device replacement, and precise, robust sample processing.     

2′,5′-Oligoadenylate synthetase-like gene highly induced by hepatitis C virus infection in human liver is inhibitory to viral replication in vitro

We found the 2′,5′-oligoadenylate synthetase-like (OASL) gene to be significantly elevated by high virus loads in human liver infected with hepatitis C virus (HCV). Here, we determined whether OASL inhibited HCV replication using an in vitro system. We constructed three expression vectors of OASL to produce isoform a (OASLa), isoform b (OASLb), and the C-terminal ubiquitin-like domain of isoform a (Ub). When Huh7 JFH-1 HCV replicon cells were separately transfected with these three vectors, colony formation of HCV-replicating cells was inhibited by 95%, 94%, and 65%, respectively. Both OASLa and OASLb were also inhibitory for cells as well as the virus because colony formation of OASL-producing cells was reduced to 41% and 8%, respectively. Stable Huh7 clones producing each of the three OASLs were established and assessed for their inhibition of HCV replication using luciferase reporter gene-containing JFH-1 replicon RNA. HCV replication was inhibited by 50-90% in several stable OASL clones. Association analysis in six Ub clones expressing different levels of Ub mRNA showed that the degree of inhibition of HCV replication was significantly associated with the amount of Ub present. In conclusion, OASL possesses two domains with HCV inhibitory activity. The N-terminal OAS-homology domain without OAS activity is inhibitory for cell growth as well as HCV replication, whereas C-terminal Ub is inhibitory only for HCV replication. Therefore, OASLa, a major isoform of this molecule induced in human liver, may mediate anti-HCV activity through two different domains.