Auxin promotes Arabidopsis root growth by modulating gibberellin response

The growth of plant organs is influenced by a stream of the phytohormone auxin that flows from the shoot apex to the tip of the root. However, until now it has not been known how auxin regulates the cell proliferation and enlargement that characterizes organ growth. Here we show that auxin controls the growth of roots by modulating cellular responses to the phytohormone gibberellin (GA). GA promotes the growth of plants by opposing the effects of nuclear DELLA protein growth repressors, one of which is Arabidopsis RGA (for repressor of gal-3). GA opposes the action of several DELLA proteins by destabilizing them, reducing both the concentration of detectable DELLA proteins and their growth-restraining effects. We also show that auxin is necessary for GA-mediated control of root growth, and that attenuation of auxin transport or signalling delays the GA-induced disappearance of RGA from root cell nuclei. Our observations indicate that the shoot apex exerts long-distance control on the growth of plant organs through the effect of auxin on GA-mediated DELLA protein destabilization.     

The v-myc oncogene is sufficient to induce growth transformation of chick neuroretina cells

A number of studies have shown that full transformation of non-established rodent fibroblasts can be efficiently achieved in vitro by the concerted action of two oncogenes belonging to different complementation groups. Extension of the two-genes carcinogenesis model to other differentiated cell types, presumably endowed with different controls of growth, is desirable for a better understanding of questions such as the host cell selectivity of oncogene action. A recent report claimed that cooperation between two oncogenes, v-myc and v-mil, is required to achieve transformation of chicken embryo neuroretina cells, which are characterized by a limited growth capacity in monolayer culture. Here we present evidence that the v-myc oncogene alone is sufficient to induce growth transformation of glial and neuronal precursor cell types from chick neuroretina. We also report that induction of transformation by v-myc is accompanied by faithful preservation of some of the differentiated functions of the chick cells.     

最大度是6的平面图是第一类图的一个充分条件

用x'(G)表示G的边染色数.对于最大度是△的可平面图G,如果X'(G)=△,称G为第一类图;如果x'(G)=△+1,称G为第二类图.运用Dischrge方法证明:最大度是6且不含7圈的可平面图G是第一类图.     

最大度为5的可平面图是第一类的充分条件

最大度是5的可平面图,既有第一类,也有第二类。该文运用Discharge方法以及临界图的一些重要性质证明,每个最大度为5且不含三圈或不含四圈或不含五圈的简单平面图的边色数等于5,即这样的平面图是第一类的。文中还给出了最大度为5的平面图分类的一个特征刻画。     

The ectodomain of Toll-like receptor 9 is cleaved to generate a functional receptor

Mammalian Toll-like receptors (TLRs) 3, 7, 8 and 9 initiate immune responses to infection by recognizing microbial nucleic acids; however, these responses come at the cost of potential autoimmunity owing to inappropriate recognition of self nucleic acids. The localization of TLR9 and TLR7 to intracellular compartments seems to have a role in facilitating responses to viral nucleic acids while maintaining tolerance to self nucleic acids, yet the cell biology regulating the transport and localization of these receptors remains poorly understood. Here we define the route by which TLR9 and TLR7 exit the endoplasmic reticulum and travel to endolysosomes in mouse macrophages and dendritic cells. The ectodomains of TLR9 and TLR7 are cleaved in the endolysosome, such that no full-length protein is detectable in the compartment where ligand is recognized. Notably, although both the full-length and cleaved forms of TLR9 are capable of binding ligand, only the processed form recruits MyD88 on activation, indicating that this truncated receptor, rather than the full-length form, is functional. Furthermore, conditions that prevent receptor proteolysis, including forced TLR9 surface localization, render the receptor non-functional. We propose that ectodomain cleavage represents a strategy to restrict receptor activation to endolysosomal compartments and prevent TLRs from responding to self nucleic acids.     

Auxin transport inhibitors block PIN1 cycling and vesicle trafficking

Polar transport of the phytohormone auxin mediates various processes in plant growth and development, such as apical dominance, tropisms, vascular patterning and axis formation. This view is based largely on the effects of polar auxin transport inhibitors. These compounds disrupt auxin efflux from the cell but their mode of action is unknown. It is thought that polar auxin flux is caused by the asymmetric distribution of efflux carriers acting at the plasma membrane. The polar localization of efflux carrier candidate PIN1 supports this model. Here we show that the seemingly static localization of PIN1 results from rapid actin-dependent cycling between the plasma membrane and endosomal compartments. Auxin transport inhibitors block PIN1 cycling and inhibit trafficking of membrane proteins that are unrelated to auxin transport. Our data suggest that PIN1 cycling is of central importance for auxin transport and that auxin transport inhibitors affect efflux by generally interfering with membrane-trafficking processes. In support of our conclusion, the vesicle-trafficking inhibitor brefeldin A mimics physiological effects of auxin transport inhibitors.     

一种充分下降的DY共轭梯度法及其收敛性

基于已有的DY方法和HZ方法,提出了一种修正的DY共轭梯度法(MDY算法)。该算法产生的搜索方向为充分下降方向,且这一性质与所采用的线搜索方法无关。在一定的条件下证明了保守MDY算法(CMDY算法)基于Armijo线搜索和Wolfe线搜索求解非凸优化问题的全局收敛性。相关的数值试验结果验证了该方法的有效性。     

关于原根存在的几个充要条件

建立关于模m原根存在的几个充要条件,分别从不同的角度揭示了当模m存在原根时所具有的一些本质特性.     

Increasing adult hippocampal neurogenesis is sufficient to improve pattern separation

Adult hippocampal neurogenesis is a unique form of neural circuit plasticity that results in the generation of new neurons in the dentate gyrus throughout life. Neurons that arise in adults (adult-born neurons) show heightened synaptic plasticity during their maturation and can account for up to ten per cent of the entire granule cell population. Moreover, levels of adult hippocampal neurogenesis are increased by interventions that are associated with beneficial effects on cognition and mood, such as learning, environmental enrichment, exercise and chronic treatment with antidepressants. Together, these properties of adult neurogenesis indicate that this process could be harnessed to improve hippocampal functions. However, despite a substantial number of studies demonstrating that adult-born neurons are necessary for mediating specific cognitive functions, as well as some of the behavioural effects of antidepressants, it is unknown whether an increase in adult hippocampal neurogenesis is sufficient to improve cognition and mood. Here we show that inducible genetic expansion of the population of adult-born neurons through enhancing their survival improves performance in a specific cognitive task in which two similar contexts need to be distinguished. Mice with increased adult hippocampal neurogenesis show normal object recognition, spatial learning, contextual fear conditioning and extinction learning but are more efficient in differentiating between overlapping contextual representations, which is indicative of enhanced pattern separation. Furthermore, stimulation of adult hippocampal neurogenesis, when combined with an intervention such as voluntary exercise, produces a robust increase in exploratory behaviour. However, increasing adult hippocampal neurogenesis alone does not produce a behavioural response like that induced by anxiolytic agents or antidepressants. Together, our findings suggest that strategies that are designed to increase adult hippocampal neurogenesis specifically, by targeting the cell death of adult-born neurons or by other mechanisms, may have therapeutic potential for reversing impairments in pattern separation and dentate gyrus dysfunction such as those seen during normal ageing.     

Myosin subfragment-1 is sufficient to move actin filaments in vitro

The rotating crossbridge model for muscle contraction proposes that force is produced by a change in angle of the crossbridge between the overlapping thick and thin filaments. Myosin, the major component of the thick filament, is comprised of two heavy chains and two pairs of light chains. Together they form two globular heads, which give rise to the crossbridge in muscle, and a coiled-coil rod, which forms the shaft of the thick filament. The isolated head fragment, subfragment-1 (S1), contains the ATPase and actin-binding activities of myosin (Fig. 1). Although S1 seems to have the requisite enzymatic activity, direct evidence that S1 is sufficient to drive actin movement has been lacking. It has long been recognized that in vitro movement assays are an important approach for identifying the elements in muscle responsible for force generation. Hynes et al. showed that beads coated with heavy meromyosin (HMM), a soluble proteolytic fragment of myosin consisting of a part of the rod and the two heads, can move on Nitella actin filaments. Using the myosin-coated surface assay of Kron and Spudich, Harada et al. showed that single-headed myosin filaments bound to glass support movement of actin at nearly the same speed as intact myosin filaments. These studies show that the terminal portion of the rod and the two-headed nature of myosin are not required for movement. To restrict the region responsible for movement further, we have modified the myosin-coated surface assay by replacing the glass surface with a nitrocellulose film. Here we report that myosin filaments, soluble myosin, HMM or S1, when bound to a nitrocellulose film, support actin sliding movement (Fig. 2). That S1 is sufficient to cause sliding movement of actin filaments in vitro gives strong support to models of contraction that place the site of active movement in muscle within the myosin head.     

NO is necessary and sufficient for egg activation at fertilization

The early steps that lead to the rise in calcium and egg activation at fertilization are unknown but of great interest--particularly with the advent of in vitro fertilization techniques for treating male infertility and whole-animal cloning by nuclear transfer. This calcium rise is required for egg activation and the subsequent events of development in eggs of all species. Injection of intact sperm or sperm extracts can activate eggs, suggesting that sperm-derived factors may be involved. Here we show that nitric oxide synthase is present at high concentration and active in sperm after activation by the acrosome reaction. An increase in nitrosation within eggs is evident seconds after insemination and precedes the calcium pulse of fertilization. Microinjection of nitric oxide donors or recombinant nitric oxide synthase recapitulates events of egg activation, whereas prior injection of oxyhaemoglobin, a physiological nitric oxide scavenger, prevents egg activation after fertilization. We conclude that nitric oxide synthase and nitric-oxide-related bioactivity satisfy the primary criteria of an egg activator: they are present in an appropriate place, active at an appropriate time, and are necessary and sufficient for successful fertilization.     

A signal sequence is not sufficient to lead beta-galactosidase out of the cytoplasm

Escherichia coli strains have been constructed in which lacZ, the gene for the cytoplasmic enzyme beta-galactosidase, is fused to lamB, the gene for an outer membrane protein. One such strain produces a beta-galactosidase which remains cytoplasmic even though it possesses the complete signal sequence of the lamB protein precursor at the amino-terminal end.     

近似非精确加速迫近梯度方法求解一类最大特征值函数极小化问题

非精确加速迫近梯度(IAPG)算法,用于解决问题min{F(X)=f(X)+g(X):X∈Sn},其中函数f:Sn→R是连续可微的,且▽f是Lipschitz连续的,函数f,g均是正常的,下半连续凸函数(可能非光滑).利用近似IAPG算法借助于非光滑函数的光滑近似,解决非光滑函数中最大特征值函数与一般非光滑函数g(x)的和的极小化问题,得出近似IAPG算法,并给出了收敛性分析.将近似IAPG算法用于求解带有线性约束的最大特征值函数的优化问题.     

整系数多项式有理根定理的改进

文章对整系数多项式有理根定理进行了推广和改进。运用本文的定理,可使整系数多项式有理根的寻求变得简便易行。     

如何引导学生养成良好的钢琴弹奏习惯

钢琴传入我国距今已有一百多年的历史,随着改革开放和音乐文化的普及与发展,钢琴进入了千家万户.然而我们发现很多学生在练琴时都存在一定的盲目性,所以练琴成效不大,如何有效地练琴达到事倍功半,是我们目前首先要解决的问题.     

超可解群的几个充分条件

设有限群G可解,G／N超可解,若N还满足下列条件之一,则G超可解：（1）N的极大子群在G中弱拟正规;（2）N＝G,且N的Sylow子群的正规化子的极大子群在G中弱拟正规;（3）N的Sylow子群的极大子群在G中弱拟正规;（4）N的Sylow子群的循环子群在G中弱拟正规。     

如何引导学生养成良好的钢琴弹奏习惯

钢琴传入我国距今已有一百多年的历史,随着改革开放和音乐文化的普及与发展,钢琴进入了千家万户。然而我们发现很多学生在练琴时都存在一定的盲目性,所以练琴成效不大,如何有效地练琴达到事倍功半,是我们目前首先要解决的问题。