Transition dynamics and selection of the distinct S-DNA and strand unpeeling modes of double helix overstretching

Recent studies have revealed two distinct pathways for the DNA overstretching transition near 65 pN: 'unpeeling' of one strand from the other, and a transition from B-DNA to an elongated double-stranded 'S-DNA' form. However, basic questions concerning the dynamics of these transitions, relative stability of the two competing overstretched states, and effects of nicks and free DNA ends on overstretching, remain open. In this study we report that: (i) stepwise extension changes caused by sequence-defined barriers occur during the strand-unpeeling transition, whereas rapid, sequence-independent extension fluctuations occur during the B to S transition; (ii) the secondary transition that often occurs following the overstretching transition is strand-unpeeling, during which the extension increases by 0.01-0.02 nm per base pair of S-DNA converted to single-stranded DNA at forces between 75 and 110 pN; (iii) even in the presence of nicks or free ends, S-DNA can be stable under physiological solution conditions; (iv) distribution of small GC-rich islands in a large DNA plays a key role in determining the transition pathways; and (v) in the absence of nicks or free ends, torsion-unconstrained DNA undergoes the overstretching transition via creation of S-DNA. Our study provides a new, high-resolution understanding of the competition between unpeeling and formation of S-DNA.     

Molecular systematics, character evolution, and pollen morphology of Cistus and Halimium (Cistaceae)

Pollen analysis and parsimony-based phylogenetic analyses of the genera Cistus and Halimium, two Mediterranean shrubs typical of Mediterranean vegetation, were undertaken, on the basis of cpDNA sequence data from the trnL-trnF, and trnS-trnG regions, to evaluate limits between the genera. Neither of the two genera examined formed a monophyletic group. Several monophyletic clades were recognized for the ingroup. (1) The ??white and whitish pink Cistus??, where most of the Cistus sections were present, with very diverse pollen ornamentations ranging from striato-reticulate to largely reticulate, sometimes with supratectal elements; (2) The ??purple pink Cistus?? clade grouping all the species with purple pink flowers belonging to the Macrostylia and Cistus sections, with rugulate or microreticulate pollen. Within this clade, the pink-flowered endemic Canarian species formed a monophyletic group, but with weak support. (3) Three Halimium clades were recovered, each with 100% bootstrap support; all Halimium species had striato-reticulate pollen. Two Halimium clades were characterized by yellow flowers, and the other by white flowers.     

Variability of cell wall polysaccharides composition and hemicellulose enzymatic profile in an apple progeny

The genetic variability of apple cell walls polysaccharides chemical composition and structure was assessed in a progeny of 141 individuals harvested over 2 years. The variability of the hemicelluloses oligosaccharides released by glucanase was analyzed by MALDI-TOF MS. The genetic contribution was distinguished from harvest year as well as from parental crossing patterns and scab resistance selection. Results showed that harvest year had a major impact on cell wall polysaccharide composition and structure. Within each harvest, genetic effect impact more significantly cell wall polysaccharide chemistry than does reciprocal crossing or early scab selection. Uronic acids, glucose, galactose and xylose contents as well as some glucomannan and xyloglucan structures have a high heritability. This first cell wall chemotyping of an apple progeny opens the way for future searches of genetic markers for the chemical variability of cell wall polysaccharides.     

ORAI-mediated calcium influx in T cell proliferation, apoptosis and tolerance

Ca²⁺ homeostasis controls a diversity of cellular processes including proliferation and apoptosis. A very important aspect of Ca²⁺ signaling is how different Ca²⁺ signals are translated into specific cell functions. In T cells, Ca²⁺ signals are induced following the recognition of antigen by the T cell receptor and depend mainly on Ca²⁺ influx through store-operated CRAC channels, which are mediated by ORAI proteins following their activation by STIM proteins. The complete absence of Ca²⁺ influx caused by mutations in Stim1 and Orai1 leads to severe immunodeficiency. Here we summarize how Ca²⁺ signals are tuned to regulate important T cell functions as proliferation, apoptosis and tolerance, the latter one being a special state of immune cells in which they can no longer respond properly to an otherwise activating stimulus. Perturbations of Ca²⁺ signaling may be linked to immune suppressive diseases and autoimmune diseases.     

Granulocytic sarcoma, an undiagnosed leukemia, initially manifested as paralysis

Granulocytic sarcoma (GS) may be a presenting sign of myelogenous leukemia. Occasionally, an extramedullary neoplasm composed from myelocytic precursor cells occurs in patients without evidence of leukemia. Rarely, undiagnosed leukemia occurs initially manifesting with paralysis to spinal cord GS. We present a case report of 20-year-old girl with an undiagnosed leukemia, initially manifesting as paralysis. En bloc spondylectomy with chemotherapy postoperatively constituted the treatment of choice for this tumor. After two courses of chemotherapy, the patient made a good postoperative recovery with notable bilateral lower extremity improvement.     

Net sodium fluxes change significantly at anatomically distinct root zones of rice (Oryza sativa L.) seedlings

Casparian bands of endodermis and exodermis play crucial roles in blocking apoplastic movement of ions and water into the stele of roots through the cortex. These apoplastic barriers differ considerably in structure and function along the developing root. The present study assessed net Na⁺ fluxes in anatomically distinct root zones of rice seedlings and analyzed parts of individual roots showing different Na⁺ uptake. The results indicated that anatomically distinct root zones contributed differently to the overall uptake of Na⁺. The average Na⁺ uptake in root zones in which Casparian bands of the endo- and exo-dermis were interrupted by initiating lateral root primordia (root zone III) was significantly greater than that at the root apex, where Casparian bands were not yet formed (root zone I), or in the region where endo- and exo-dermis with Casparian bands were well developed (root zone II). The measurement of net Na⁺ fluxes using a non-invasive scanning ion-selective electrode technique (SIET) demonstrated that net Na⁺ flux varied significantly in different positions along developing rice roots, and a net Na⁺ influx was obvious at the base of young lateral root primordia. Since sodium fluxes changed significantly along developing roots of rice seedlings, we suggest that the significantly distinct net Na⁺ flux profile may be attributed to different apoplastic permeability due to lateral root primordia development for non-selective apoplastic bypass of ions along the apoplast.     

Lycopene protects against trimethyltin-induced neurotoxicity in primary cultured rat hippocampal neurons by inhibiting the mitochondrial apoptotic pathway

Lycopene is a potent free radicals scavenger with demonstrated protective efficacy in several experimental models of oxidative damage. Trimethyltin (TMT) is an organotin compound with neurotoxic effects on the hippocampus and other limbic structures and is used to model neurodegenerative diseases targeting these brain areas. Oxidative stress is widely accepted as a central pathogenic mechanism of TMT-mediated neurotoxicity. The present study investigated whether the plant carotene lycopene protects against TMT-induced neurotoxicity in primary cultured rat hippocampal neurons. Lycopene pretreatment improved cell viability in TMT-treated hippocampal neurons and inhibited neuronal apoptosis. Microfluorometric imaging revealed that lycopene inhibited the accumulation of mitochondria-derived reactive oxygen species (ROS) during TMT exposure. Moreover, lycopene ameliorated TMT-induced activation of the mitochondrial permeability transition pore (mPTP) and the concomitant depolarization of the mitochondrial membrane potential (ΔΨ_m). Consequently, cytochrome c release from the mitochondria and ensuing caspase-3 activation were markedly reduced. These findings reveal that lycopene protects against TMT-induced neurotoxicity by inhibiting the mitochondrial apoptotic pathway. The anti-apoptotic effect of lycopene on hippocampal neurons highlights the therapeutic potential of plant-derived antioxidants against neurodegenerative diseases.     

IL-13促进肝星状细胞增殖和胶原蛋白表达

肝星状细胞(hepatic stellate cell,HSC)是肝纤维化发展过程中过量细胞外基质的主要来源。该研究首先利用MTT法检测IL-13实验剂量和时间条件下肝星状细胞增殖情况;然后运用RT-PCR技术检测IL-13对人肝星状细胞LX-2细胞系IL-13Rα1、IL-4Rα、TGF-β和Ⅰ型胶原蛋白转录水平的影响;最后通过羟脯氨酸法定量分析各组细胞培养上清液中的胶原蛋白含量。结果发现:IL-13能促进肝星状细胞的增殖;在不改变IL-13Rα1和IL-4Rα转录水平的同时,对TGF-β和Ⅰ型胶原蛋白mRNA的表达以及细胞总胶原蛋白含量的上调作用均呈现出较为明显的剂量和时间依赖性。     

斑背大尾莺繁殖期鸣声行为分析

2009年5-7月,在辽宁双台河口保护区录制了20只繁殖期斑背大尾莺雄性个体的鸣声.根据行为特征,该鸟鸣声定义为3种鸣声类型:求偶炫耀鸣唱、报警声和联络声.利用Wavesurfer软件对20只斑背大尾莺雄性个体543个鸣声的句子持续时间、句子音节个数、音节持续时间、音节间隔时间等4个参数进行分析测量,发现求偶炫耀鸣唱由节奏逐渐加快的前部句子和音节组成复杂的主体部两个句子组成; 报警声和联络声的句子均由单音节组成.音节类型总数为38种,其中包括前部句子的音节类型6种.采用单因素方差分析(one-way ANOVA)对求偶炫耀鸣唱的4个参数进行差异性检验发现,不同个体的各个参数均呈极显著差异(P<0.01).     

A critical role of mitochondrial phosphatase Ptpmt1 in embryogenesis reveals a mitochondrial metabolic stress-induced differentiation checkpoint in embryonic stem cells

Mitochondria are highly dynamic organelles that play multiple roles in cells. How mitochondria cooperatively modulate embryonic stem (ES) cell function during development is not fully understood. Global disruption of Ptpmt1, a mitochondrial Pten-like phosphatidylinositol phosphate (PIP) phosphatase, resulted in developmental arrest and postimplantation lethality. Ptpmt1(-/-) blastocysts failed to outgrow, and inner-cell-mass cells failed to thrive. Depletion of Ptpmt1 in conditional knockout ES cells decreased proliferation without affecting energy homeostasis or cell survival. Differentiation of Ptpmt1-depleted ES cells was essentially blocked. This was accompanied by upregulation of cyclin-dependent kinase inhibitors and a significant cell cycle delay. Reintroduction of wild-type but not of catalytically deficient Ptpmt1 C132S or truncated Ptpmt1 lacking the mitochondrial localization signal restored the differentiation capabilities of Ptpmt1 knockout ES cells. Intriguingly, Ptpmt1 is specifically important for stem cells, as ablation of Ptpmt1 in differentiated embryonic fibroblasts did not disturb cellular function. Further analyses demonstrated that oxygen consumption of Ptpmt1-depleted cells was decreased, while glycolysis was concomitantly enhanced. In addition, mitochondrial fusion/dynamics were compromised in Ptpmt1 knockout cells due to accumulation of PIPs. These studies, while establishing a crucial role for Ptpmt1 phosphatase in embryogenesis, reveal a mitochondrial metabolic stress-activated checkpoint in the control of ES cell differentiation.