Physical Blocking Neural Tube Closure Affects Radial Intercalation and Neural Crest Midline-directed Migration in Xenopus Dorsal Explants

神经管闭合缺陷(NTDs)是一种严重的先天畸形疾病,在新生儿中有千分之一的发病率.神经管融合前后,多种组织参与形态发生运动.神经管一经融合,神经嵴细胞就会向背侧中线方向产生单极突出并向此方向迁移形成神经管的顶部.与此同时,神经管从腹侧开始发生辐射状切入以实现单层化.在此,我们在非洲爪蟾的移植体中机械阻断神经管的闭合以检测其细胞运动及随后的图式形成.结果显示神经管闭合缺陷的移植体不能形成单层化的神经管,并且神经嵴细胞滞留在侧面区域不能向背侧中线迁移,而对神经前体标记基因的检测显示神经管的背腹图式形成并未受到影响.以上结果表明神经管的融合对于辐射状切入和神经嵴细胞向背侧中线方向的迁移过程是必需的,而对于神经管的沿背腹轴方向的图式形成是非必需的.

Determinations of MC-LR and [Dha(7)] MC-LR Concentrations and Physicochemical Properties by Liquid Chromatography-Tandem Mass Spectrometry

A liquid chromatography electrospray mass spectrometry (LC/ESI/MS) method working in multiple reactions monitoring mode for the determination of trace amounts of microcystin variants (MC-LR and [Dha(7)] MC-LR) in waters was developed. The limit of quantification was 0.05 mu g/L and the limit of detection was 0.015 mu g/L for MC-LR and [Dha(7)] MC-LR, respectively. Recoveries for MCs were in the range of 68%-81%. MC-LR and [Dha(7)] MC-LR were chemically stable with similar physiochemical behavior.

Rapid quantification of total microcystins in cyanobacterial samples by periodate-permanganate oxidation and reversed-phase liquid chromatography

Microcystins (MCs) comprise a family of more than 80 related cyclic hepatotoxic heptapeptides. Oxidation of MCs causes cleavage of the chemically unique C-20 beta-amino acid (2S, 3S, 8S, 9S)-3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid (Adda) amino to form 2-methyl-3-methoxy-4-phenylbutanoic acid (MMPB), which has been exploited to enable analysis of the entire family. In the present study, the reaction conditions (e.g. concentration of the reactants. temperature and pH) used in the production of MMPB by oxidation of cyanobacterial samples with permanganate-periodate were optimized through a series of well-controlled batch experiments. The oxidation product (MMPB) was then directly analyzed by high-performance liquid chromatography with diode array detection. The results of this study provided insight into the influence of reaction conditions on the yield of MMPB. Specifically, the optimal conditions, including a high dose of permanganate (>= 50 mM) in saturated periodate solution at ambient temperature under alkaline conditions (pH similar to 9) over 1-4 h were proposed, as indicated by a MMPB yield of greater than 85%. The technique developed here was applied to determine the total concentration of MCs in cyanobacterial bloom samples, and indicated that the MMPB technique was a highly sensitive and accurate method of quantifying total MCs. Additionally, these results will aid in development of a highly effective analytical method for detection of MMPB as an oxidation product for evaluation of total MCs in a wide range of environmental sample matrices, including natural waters, soils (sediments) and animal tissues. (C) 2009 Elsevier B.V. All rights reserved.

Simultaneous determination of microcystin-LR and its glutathione conjugate in fish tissues by liquid chromatography-tandem mass spectrometry

A sensitive and selective liquid chromatography-tandem mass spectrometry method was developed and validated for the simultaneous quantitative determination of microcystin-LR (MC-LR) and its glutathione conjugate (MC-LR-GSH) in fish tissues. The analytes were extracted from fish liver and kidney using 0.01 M EDTA-Na-2-5% acetic acid, followed by a solid-phase extraction (SPE) on Oasis HLB and silica cartridges. High-performance liquid chromatography (HPLC) with electrospray ionization mass spectrometry, operating in selected reaction monitoring (SRM) mode, was used to quantify MC-LR and its glutathione conjugate in fish liver and kidney. Recoveries of analytes were assessed at three concentrations (0.2, 1.0, and 5 mu g g(-1) dry weight [DW]) and ranged from 91 to 103% for MC-LR, and from 65.0 to 75.7% for MC-LR-GSH. The assay was linear within the range from 0.02 to 5.0 mu g g(-1) DW, with a limit of quantification (LOQ) of 0.02 mu g g(-1) DW. The limit of detection (LOD) of the method was 0.007 mu g g(-1) DW in both fish liver and kidney. The overall precision was determined on three different days. The values for within- and between-day precision in liver and kidney were within 15%. This method was applied to the identification and quantification of MC-LR and its glutathione conjugate in liver and kidney of fish with acute exposure of MC-LR. (c) 2007 Elsevier B.V. All rights reserved.

Headspace solid-phase microextraction with novel sol-gel permethylated-beta-cyclodextrin/hydroxyl-termination silicone oil fiber for determination of polybrominated diphenyl ethers by gas chromatography-mass spectrometry in soil

A simple, sensitive, and accurate method for determination of polybrominated diphenyl ethers (PBDEs) in soil has been developed based on headspace solid-phase microextraction (HS-SPME) followed by gas chromatography-mass spectrometry (GC-MS). Permethylated-beta-cyclodextrin/hydroxyl-termination silicone oil (PM-beta-CD/OH-TSO) fiber was first prepared by sol-gel technology and employed in SPME procedure. By exploiting the superiorities of sot-gel coating technique and the advantages of the high hydrophobic doughnut-shaped cavity of PM-beta-CD, the novel fiber showed desirable operational stability and extraction ability. After optimization on extraction conditions like water addition, extraction temperature, extraction time, salts effect, and solvents addition, the method was validated in soil samples, achieving good linearity (r>0.999), precision (R.S.D. < 10%), accuracy (recovery>78%), and detection limits (S/N =3) raging from 13.0 to 78.3 pg/g. (c) 2007 Published by Elsevier B.V.

Determination of sexual hormones in liquid cosmetics by polymer monolith microextraction coupled with high performance liquid chromatography

A method was presented for the determination of testosterone, methyltestosterone and progesterone in liquid cosmetics by coupling polymer monolith microextraction (PMME) to high performance liquid chromatography with UV detection. A poly (methacrylic acid-ethylene glycol dimethacrylate) monolithic capillary column was selected as the extraction medium, which showed high extraction capacity towards these compounds. To achieve optimum extraction performance, several parameters relating to PMME were investigated, including extraction flow rate and pH value, inorganic salt and organic phase concentration of the sample matrix. By simple dilution with phosphate solution and filtering, the sample solution then could be directly injected into the device for extraction. The limits of detection of testosterone, methyltestosterone and progesterone were calculated to be 2, 3, 2, 8 and 4.6 mu g/L. Good linearity was achieved in the range of 10 to 1000 mu g/L with a linear coefficient. r value above 0. 996. Excellent method reproducibility was found by intra- and inter-day precisions, yielding the relative standard deviations of < 7. 7 % and < 7. 5 %, respectively. Recovery for them in the real samples was between 83% and 119%.

Modeling phytoplankton dynamics in the River Darling (Australia) using the radial basis function neural network

A radial basis function neural network was employed to model the abundance of cyanobacteria. The trained network could predict the populations of two bloom forming algal taxa with high accuracy, Nostocales spp. and Anabaena spp., in the River Darling, Australia. To elucidate the population dynamics for both Nostocales spp. and Anabaena spp., sensitivity analysis was performed with the following results. Total Kjeldahl nitrogen had a very strong influence on the abundance of the two algal taxa, electrical conductivity had a very strong negative relationship with the population of the two algal species, and flow was identified as one dominant factor influencing algal blooms after a scatter plot revealed that high flow could significantly reduce the algal biomass for both Nostocales spp. and Anabaena spp. Other variables such as turbidity, color, and pH were less important in determining the abundance and succession of the algal blooms.

Analysis of estrogens in environmental waters using polymer monolith in-polyether ether ketone tube solid-phase microextraction combined with high-performance liquid chromatography

A simple, rapid and sensitive on-line method for simultaneous determination of four endocrine disruptors (17 beta-estradiol, estriol, bisphenol A and 17 alpha-ethinylestradiol) in environmental waters was developed by coupling in-tube solid-phase microextraction (SPME) to high-performance liquid chromatography (HPLC) with fluorescence detection (FLD). A poly(acrylamide-vinylpyridine-NAP-methylene bisacrylamide) monolith, synthesized inside a polyether ether ketone (PEEK) tube, was selected as the extraction medium. To achieve optimum extraction performance, several parameters were investigated, including extraction flow-rate, extraction time, and pH value, inorganic salt and organic solvent content of the sample matrix. By simply filtered with nylon membrane filter and adjusting the pH of samples to 6.0 with phosphoric acid, the sample solution then could be directly injected into the device for extraction. Low detection limits (S/N = 3) and quantification limits (S/N = 10) of the proposed method were achieved in the range of 0.006-0.10 ng/mL and 0.02-0.35 ng/mL from spiked lake waters, respectively. The calibration curves of four endocrine disruptors showed good linearity ranging from quantification limits to 50 ng/mL with a linear coefficient R-2 value above 0.9913. Good method reproducibility was also found by intra- and inter-day precisions, yielding the RSDs less than 12 and 9.8%, respectively. Finally, the proposed method was successfully applied to the determination of these compounds in several environmental waters. (c) 2006 Elsevier B.V. All rights reserved.

Determination of odorous compounds in water by headspace solid-phase microextraction-gas chromatography-mass spectrometry

Three major odorous compounds are 2-methylisoborneol ( 2-MIB), geosmin and beta-cyclocitral, which in water were determined by coupling headspace solid-phase microextraction ( HS-SPME) with gas chromatography-mass spectrometry (GC-MS). The operating conditions of HS-SPME, such as fibre type, salt concentration, water temperature, stirring, absorption time and desorption time were studied and discussed.The highest absorption of the odorous compounds were obtained under the following operating conditions as the addition of 30% ( m/V) NaCl, stirring at 60 degrees C for 40 min, using 65 mu m polydimethyl siloxane/divinylbenzene coated fibre. After the odorous compounds had been absorbed in the fibre under the optimal conditions of HSSPME, they were desorbed at 250 degrees C and determined by GC-MS. The limits of detection for geosmin, beta-cyclocitral and 2-MIB in water were 1. 0, 1. 3, 1. 7 ng/L, and the relative standard deviations for them were 4. 9%, 8. 4%, 6. 2%,respectively. There were good linear correlation (the calibration coefficients were all above 0. 997) for the three odorous compounds in the range of 5 similar to 1000 ng/ L. Therefore, trace levels of the odorous compounds at ng/L in water could be quantified by the simple method with satisfactory result.

Determination of 266 pesticide residues in apple juice by matrix solid-phase dispersion and gas chromatography-mass selective detection

A macro matrix solid-phase dispersion (MSPD) method was developed to extract 266 pesticides from apple juice samples prior to gas chromatography-mass selective detection (GC-MSD) determination. A 10 g samples was mixed with 20 g diatomaceous earth. The mixture was transferred into a glass column. Pesticide residues were leached with a 160 mL hexane-dichloromethane (1:1) at 5 mL/min. Two hundred and sixty-six pesticides were divided into three groups and detected by GC-MSD under selective ion monitoring. The proposed method takes advantage of both liquid-liquid extraction and conventional MSPD methods. Application was illustrated by the analysis of 236 apple juice samples produced in Shaanxi province China mainland this year. (C) 2004 Elsevier B.V. All rights reserved.