Chromosome organization revealed upon the decondensation of telophase chromosomes inAllium

Chromosomes of root tip cells ofAllium cepa andAllium sativum were studied in early, middle and late telophase to examine the organization of mitotic chromosomes, taking advantage of the naturally occurring chromosome dispersion during the process of decondensation in telophase. Longitudinal and transverse sections of telophase chromosomes viewed under the transmission electron microscope showed that mitotic chromosomes inAllium were composed of helically coiled 400–550 nm chromatin fibres. In some regions of the longitudinal sections, these chromatin fibres were seen to be orientated parallel to one another but formed roughly a right angle to the long axis of the chromosome. In transverse sections, the telophase chromosome appeared to have a hollow centre encircled by the 400–550 nm chromatin fibre which in turn was a hollow tube structure formed by the coiling of a thinner fibre of 170–200 nm. In addition, cross views of chromatin fibres of 170–200 nm and 50–70 nm were also identified in telophase chromosome preparations. These two organizational levels of chromatin fibres also showed a hollow centre. The process of decondensation of telophase chromosomes is described, and some morphological characteristics associated with the activities of chromosome decondensation are analysed. Based on the observations made onAllium chromosomes in this study, various models of chromosome organization are discussed.     

Nitrate Uptake and Partitioning by Corn {Zea mays L.) Root Systems and Associated Morphological Differences among Genotypes and Stages of Root Development

Pan, W. L., Jackson, W. A. and Moll, R. H. 1985. Nitrate uptakeand partitioning by corn (Zea mays L.) root systems and associatedmorphological differences among genotypes and stages of rootdevelopment.—J. exp. Bot, 36: 1341–1351 Nitrate uptake and partitioning by root systems of corn inbredlines were examined. Six-day-old root systems of decapitatedseedlings of seven corn inbred lines were shown to differ markedlyin their capacity for nitrate uptake and partitioning. The magnitudeof nitrate uptake ranged from 44–86 µmol NO^–₃g ^–1 fr. wt. during an 8 h period. Relative nitrate translocation(% of total uptake) also varied among the seven genotypes from4–25%, and differences in the proportions accumulated(28–73%) and reduced (22–58%) were observed. Threeof these genotypes were then examined at 5,6, and 8 d aftergermination to determine the effect of lateral root proliferationon the previously observed differences in nitrate uptake andpartitioning. Nitrate translocation per unit mass increasedwith root elongation and lateral root proliferation, and genotypicdifferences in this partitioning process were associated withdifferences in these morphological parameters. In contrast,differences among genotypes in their capability to accumulatenitrate were not correlated with these differences in morphology.Evaluations of genotypic differences in nitrate uptake and partitioningat the seedling stage should include the rate and characteristicsof morphological development Key words: Lateral root, root morphology, nitrate translocation     

用笛卡儿座标对菲氏叶猴和黑叶猴颅骨的比较形态研究

本文利用三维笛卡儿空间座标对菲氏叶猴(Presbytis phayrei)和黑叶猴(P.francoisi)颅骨的形态结构作了比较研究,描绘了它们的侧视和俯视投影图形。结果表明,两种投影图形均显示黑叶猴的颅骨大于菲氏叶猴,且显著性增大的区域出现在眉点、囟门、枕骨大孔附近和下颌骨体的高度。但菲氏叶猴较黑叶猴具有更凸的面颅。据枕骨隆突至眉点的侧视投影弧长,两种叶猴的数学模式均为:Y=a+bX-cX~2(R=0.92)。从侧视投影看,两种叶猴自枕骨隆突至眉点主要表出大小的不同。若据俯视投影图,两种颅骨的差异主要出现在外耳道以前的部分。黑叶猴较菲氏叶猴具有十分显著性增高的下颌骨体以及相对应更发达的咬肌和咀嚼器官,这很可能与它取食更多的果类食物有关。     

Slit2 Inactivates GSK3β to Signal Neurite Outgrowth Inhibition

Slit molecules comprise one of the four canonical families of axon guidance cues that steer the growth cone in the developing nervous system. Apart from their role in axon pathfinding, emerging lines of evidence suggest that a wide range of cellular processes are regulated by Slit, ranging from branch formation and fasciculation during neurite outgrowth to tumor progression and to angiogenesis. However, the molecular and cellular mechanisms downstream of Slit remain largely unknown, in part, because of a lack of a readily manipulatable system that produces easily identifiable traits in response to Slit. The present study demonstrates the feasibility of using the cell line CAD as an assay system to dissect the signaling pathways triggered by Slit. Here, we show that CAD cells express receptors for Slit (Robo1 and Robo2) and that CAD cells respond to nanomolar concentrations of Slit2 by markedly decelerating the rate of process extension. Using this system, we reveal that Slit2 inactivates GSK3β and that inhibition of GSK3β is required for Slit2 to inhibit process outgrowth. Furthermore, we show that Slit2 induces GSK3β phosphorylation and inhibits neurite outgrowth in adult dorsal root ganglion neurons, validating Slit2 signaling in primary neurons. Given that CAD cells can be conveniently manipulated using standard molecular biological methods and that the process extension phenotype regulated by Slit2 can be readily traced and quantified, the use of a cell line CAD will facilitate the identification of downstream effectors and elucidation of signaling cascade triggered by Slit.     

重型/危重型新型冠状病毒肺炎关键治疗技术研究进展

新型冠状病毒(SARS-CoV-2)引发的肺炎疫情严重威胁广大人民群众身体健康和生命安全,对我国的经济发展和社会稳定产生重大影响。由于新型冠状病毒的传染性强、传播速度快、致死率较高,且尚无有效疫苗和药物来防治,少数患者迅速进展为重型、危重型甚至死亡。如何精准抗SARS-CoV-2、阻断新冠肺炎进展并改善患者预后是当下医药卫生界的研究热点。主要围绕重型、危重型新冠肺炎最新治疗手段研究进展进行综述。     

Epidermal restriction confers robustness to organ shapes

The shape of comparable tissues and organs is consistent among individuals of a given species, but how this consistency or robustness is achieved remains an open question. The interaction between morphogenetic factors determines organ formation and subsequent shaping, which is ultimately a mechanical process. Using a computational approach, we show that the epidermal layer is essential for the robustness of organ geometry control. Specifically, proper epidermal restriction allows organ asymmetry maintenance, and the tensile epidermal layer is sufficient to suppress local variability in growth, leading to shape robustness. The model explains the enhanced organ shape variations in epidermal mutant plants. In addition, differences in the patterns of epidermal restriction may underlie the initial establishment of organ asymmetry. Our results show that epidermal restriction can answer the longstanding question of how cellular growth noise is averaged to produce precise organ shapes, and the findings also shed light on organ asymmetry establishment.     

New mechanism of nerve injury in Alzheimer’s disease: β‐amyloid‐induced neuronal pyroptosis

The present study was designed to investigate the role of β‐amyloid (Aβ_1‐42) in inducing neuronal pyroptosis and its mechanism. Mice cortical neurons (MCNs) were used in this study, LPS + Nigericin was used to induce pyroptosis in MCNs (positive control group), and Aβ_1‐42 was used to interfere with MCNs. In addition, propidium iodide (PI) staining was used to examine cell permeability, lactate dehydrogenase (LDH) release assay was employed to detect cytotoxicity, immunofluorescence (IF) staining was used to investigate the expression level of the key protein GSDMD, Western blot was performed to detect the expression levels of key proteins, and enzyme‐linked immunosorbent assay (ELISA) was utilized to determine the expression levels of inflammatory factors in culture medium, including IL‐1β, IL‐18 and TNF‐α. Small interfering RNA (siRNA) was used to silence the mRNA expression of caspase‐1 and GSDMD, and Aβ_1‐42 was used to induce pyroptosis, followed by investigation of the role of caspase‐1‐mediated GSDMD cleavage in pyroptosis. In addition, necrosulfonamide (NSA), an inhibitor of GSDMD oligomerization, was used for pre‐treatment, and Aβ_1‐42 was subsequently used to observe the pyroptosis in MCNs. Finally, AAV9‐siRNA‐caspase‐1 was injected into the tail vein of APP/PS1 double transgenic mice (Alzheimer's disease mice) for caspase‐1 mRNA inhibition, followed by observation of behavioural changes in mice and measurement of the expression of inflammatory factors and pyroptosis‐related protein. As results, Aβ_1‐42 could induce pyroptosis in MCNs, increase cell permeability and enhance LDH release, which were similar to the LPS + Nigericin‐induced pyroptosis. Meanwhile, the expression levels of cellular GSDMD and p30‐GSDMD were up‐regulated, the levels of NLRP3 inflammasome and GSDMD‐cleaved protein caspase‐1 were up‐regulated, and the levels of inflammatory factors in the medium were also up‐regulated. siRNA intervention in caspase‐1 or GSDMD inhibited Aβ_1‐42‐induced pyroptosis, and NSA pre‐treatment also caused the similar inhibitory effects. The behavioural ability of Alzheimer's disease (AD) mice was relieved after the injection of AAV9‐siRNA‐caspase‐1, and the expression of pyroptosis‐related protein in the cortex and hippocampus was down‐regulated. In conclusion, Aβ_1‐42 could induce pyroptosis by GSDMD protein, and NLRP3‐caspase‐1 signalling was an important signal to mediate GSDMD cleavage, which plays an important role in Aβ_1‐42‐induced pyroptosis in neurons. Therefore, GSDMD is expected to be a novel therapeutic target for AD.