Stage-specific control of neuronal migration by somatostatin.

Developing neurons transiently express somatostatin and its receptors, but little is known about their function at these early stages. As we thought that endogenous somatostatin might control the migratory behaviour of immature neurons, we have examined the effects of somatostatin in cerebellar granule cells of early postnatal mice, because these cells express all five types of somatostatin receptors before the initiation of their migration. Here we show that somatostatin has opposite and stage-specific effects on the migration of cerebellar granule cells. Activation of somatostatin receptors increases the rate of granule cell migration near their birthplace, but decreases the rate near their final destination. Furthermore, somatostatin enhances the size and frequency of spontaneous Ca2+ fluctuations in the early phase of migration, whereas it eliminates spike-like Ca2+ transients in the late phase. Somatostatin-induced changes at both early and late phases are reversed by a blockade of K+ channel activity. These results indicate that somatostatin may provide an essential cue for accelerating the movement of granule cells in the early phase and for terminating the movement in the late phase through altering intracellular Ca2+ concentrations and K+ channel activity.     

L1 mono- and polyclonal antibodies modify cell migration in early postnatal mouse cerebellum

A major event of nervous system development is the migration of granule cell neurones, during the early postnatal development of the cerebellar cortex, from their germinating zone in the external granular layer to their final location in the internal granular layer. During migration, many granule cells are seen in direct cell-surface contact with processes of Bergmann glia, a subclass of astrocytes. In the neurological mutant mouse weaver, however, migration of granule cells is impaired, probably due to a deficit in cell-cell interactions. To gain insight into the cellular and molecular mechanisms involved in granule cell migration, we have used a modification of an in vitro assay system, previously described by Moonen et al., which displays migratory behaviour in small tissue explants during several days of suspension culture. The aim of this study was to investigate the process of granule cell migration by using antibodies directed against cell-surface components of developing neural cells. We report here that migration of 3H-thymidine-labelled granule cell neurones can be modified by Fab fragments of both mono- and polyclonal L1 antibodies, but not by Fab fragments of polyclonal antibodies prepared against mouse liver membranes, which also react with cerebellar cell surfaces.     

Bmi1 is essential for cerebellar development and is overexpressed in human medulloblastomas

Overexpression of the polycomb group gene Bmi1 promotes cell proliferation and induces leukaemia through repression of Cdkn2a (also known as ink4a/Arf) tumour suppressors. Conversely, loss of Bmi1 leads to haematological defects and severe progressive neurological abnormalities in which de-repression of the ink4a/Arf locus is critically implicated. Here, we show that Bmi1 is strongly expressed in proliferating cerebellar precursor cells in mice and humans. Using Bmi1-null mice we demonstrate a crucial role for Bmi1 in clonal expansion of granule cell precursors both in vivo and in vitro. Deregulated proliferation of these progenitor cells, by activation of the sonic hedgehog (Shh) pathway, leads to medulloblastoma development. We also demonstrate linked overexpression of BMI1 and patched (PTCH), suggestive of SHH pathway activation, in a substantial fraction of primary human medulloblastomas. Together with the rapid induction of Bmi1 expression on addition of Shh or on overexpression of the Shh target Gli1 in cerebellar granule cell cultures, these findings implicate BMI1 overexpression as an alternative or additive mechanism in the pathogenesis of medulloblastomas, and highlight a role for Bmi1-containing polycomb complexes in proliferation of cerebellar precursor cells.     

Essential role of the mitochondrial apoptosis-inducing factor in programmed cell death

Programmed cell death is a fundamental requirement for embryogenesis, organ metamorphosis and tissue homeostasis. In mammals, release of mitochondrial cytochrome c leads to the cytosolic assembly of the apoptosome-a caspase activation complex involving Apaf1 and caspase-9 that induces hallmarks of apoptosis. There are, however, mitochondrially regulated cell death pathways that are independent of Apaf1/caspase-9. We have previously cloned a molecule associated with programmed cell death called apoptosis-inducing factor (AIF). Like cytochrome c, AIF is localized to mitochondria and released in response to death stimuli. Here we show that genetic inactivation of AIF renders embryonic stem cells resistant to cell death after serum deprivation. Moreover, AIF is essential for programmed cell death during cavitation of embryoid bodies-the very first wave of cell death indispensable for mouse morphogenesis. AIF-dependent cell death displays structural features of apoptosis, and can be genetically uncoupled from Apaf1 and caspase-9 expression. Our data provide genetic evidence for a caspase-independent pathway of programmed cell death that controls early morphogenesis.     

Selective killing of cancer cells by a small molecule targeting the stress response to ROS

Malignant transformation, driven by gain-of-function mutations in oncogenes and loss-of-function mutations in tumour suppressor genes, results in cell deregulation that is frequently associated with enhanced cellular stress (for example, oxidative, replicative, metabolic and proteotoxic stress, and DNA damage). Adaptation to this stress phenotype is required for cancer cells to survive, and consequently cancer cells may become dependent upon non-oncogenes that do not ordinarily perform such a vital function in normal cells. Thus, targeting these non-oncogene dependencies in the context of a transformed genotype may result in a synthetic lethal interaction and the selective death of cancer cells. Here we used a cell-based small-molecule screening and quantitative proteomics approach that resulted in the unbiased identification of a small molecule that selectively kills cancer cells but not normal cells. Piperlongumine increases the level of reactive oxygen species (ROS) and apoptotic cell death in both cancer cells and normal cells engineered to have a cancer genotype, irrespective of p53 status, but it has little effect on either rapidly or slowly dividing primary normal cells. Significant antitumour effects are observed in piperlongumine-treated mouse xenograft tumour models, with no apparent toxicity in normal mice. Moreover, piperlongumine potently inhibits the growth of spontaneously formed malignant breast tumours and their associated metastases in mice. Our results demonstrate the ability of a small molecule to induce apoptosis selectively in cells that have a cancer genotype, by targeting a non-oncogene co-dependency acquired through the expression of the cancer genotype in response to transformation-induced oxidative stress.     

虾青素抑制H2O2诱导的HeLa细胞凋亡

为了阐明虾青素的抗氧化作用与细胞凋亡的关系,探究虾青素预处理对H_2O_2诱导HeLa细胞氧化应激的影响.通过CCK-8、活性氧探针染色、流式细胞术、蛋白质免疫印迹、实时荧光定量pcr等,分别检测细胞存活率和活性氧的积累、细胞凋亡、蛋白含量、基因相对表达量改变.结果表明虾青素预处理组细胞活力较对照组提高了29.54%以上且其可以将H_2O_2诱导的活性氧降低至对照水平,同时提高Nrf2蛋白表达量3倍之多,过氧化氢酶基因相对表达量1.5倍.说明虾青素可以有效缓解H_2O_2诱导的HeLa细胞氧化应激,从而抑制细胞凋亡.     

Mice cloned from olfactory sensory neurons

Cloning by nuclear transplantation has been successfully carried out in various mammals, including mice. Until now mice have not been cloned from post-mitotic cells such as neurons. Here, we have generated fertile mouse clones derived by transferring the nuclei of post-mitotic, olfactory sensory neurons into oocytes. These results indicate that the genome of a post-mitotic, terminally differentiated neuron can re-enter the cell cycle and be reprogrammed to a state of totipotency after nuclear transfer. Moreover, the pattern of odorant receptor gene expression and the organization of odorant receptor genes in cloned mice was indistinguishable from wild-type animals, indicating that irreversible changes to the DNA of olfactory neurons do not accompany receptor gene choice.     

线粒体去乙酰化酶SIRT3与衰老疾病

线粒体去乙酰化酶SIRT3是酵母Sir2同源蛋白,通过对线粒体多种蛋白质赖氨酸的去乙酰化修饰,它可以调控多种代谢过程,如脂肪酸的β-氧化作用、TCA循环、氧化磷酸化等.SIRT3可参与氧化应激反应,降低细胞内ROS水平;也可以作为一种肿瘤抑制因子,促进细胞的凋亡.在某些乳腺癌细胞中,SIRT3表达下调.敲除SIRT3或者SIRT3表达降低,可影响与代谢相关的衰老性疾病如心脏疾病、癌症等的发生.论文总结了近年去乙酰化酶SIRT3在代谢调控及癌症细胞凋亡中的分子机制以及SIRT3与心脏疾病、癌症的相互关系,希望为衰老疾病的预防和治疗提供一定的理论基础.     

Purkinje neuron synchrony elicits time-locked spiking in the cerebellar nuclei

An unusual feature of the cerebellar cortex is that its output neurons, Purkinje cells, release GABA (γ-aminobutyric acid). Their high intrinsic firing rates (50?Hz) and extensive convergence predict that their target neurons in the cerebellar nuclei would be largely inhibited unless Purkinje cells pause their spiking, yet Purkinje and nuclear neuron firing rates do not always vary inversely. One indication of how these synapses transmit information is that populations of Purkinje neurons synchronize their spikes during cerebellar behaviours. If nuclear neurons respond to Purkinje synchrony, they may encode signals from subsets of inhibitory inputs. Here we show in weanling and adult mice that nuclear neurons transmit the timing of synchronous Purkinje afferent spikes, owing to modest Purkinje-to-nuclear convergence ratios (～40:1), fast inhibitory postsynaptic current kinetics (τ(decay) = 2.5?ms) and high intrinsic firing rates (～90?Hz). In vitro, dynamically clamped asynchronous inhibitory postsynaptic potentials mimicking Purkinje afferents suppress nuclear cell spiking, whereas synchronous inhibitory postsynaptic potentials entrain nuclear cell spiking. With partial synchrony, nuclear neurons time-lock their spikes to the synchronous subpopulation of inputs, even when only 2 out of 40 afferents synchronize. In vivo, nuclear neurons reliably phase-lock to regular trains of molecular layer stimulation. Thus, cerebellar nuclear neurons can preferentially relay the spike timing of synchronized Purkinje cells to downstream premotor areas.     

Nitric oxide damages neuronal mitochondria and induces apoptosis in neurons

The cytotoxic effect of nitric oxide on primarily cultured rat cerebellar granule cells was studied, and the mechanisms were discussed. The results showed that nitric oxide donor S-nitroso-N-acetyl-penicillamine (SNAP; 500 μmol/L) could induce apoptosis in immature cultures of cerebellar granule cells. Flow cytometry and HPLC analyses revealed that after treatment with SNAP, the mitochondrial transmembrane potential and the cellular ATP content decreased significantly. Nitric oxide scavenger hemoglobin could effectively prevent the neuronal mitochondria from dysfunction and attenuate apoptosis. The results suggested that nitric oxide activated the apoptotic program by inhibiting the activity of mitochondrial respiratory chain and thus decreasing the cellular ATP content.     

Stargazin regulates synaptic targeting of AMPA receptors by two distinct mechanisms

Stargazer, an ataxic and epileptic mutant mouse, lacks functional AMPA (alpha-amino-3-hydroxyl-5-methyl-4-isoxazolepropionate) receptors on cerebellar granule cells. Stargazin, the mutated protein, interacts with both AMPA receptor subunits and synaptic PDZ proteins, such as PSD-95. The interaction of stargazin with AMPA receptor subunits is essential for delivering functional receptors to the surface membrane of granule cells, whereas its binding with PSD-95 and related PDZ proteins through a carboxy-terminal PDZ-binding domain is required for targeting the AMPA receptor to synapses. Expression of a mutant stargazin lacking the PDZ-binding domain in hippocampal pyramidal cells disrupts synaptic AMPA receptors, indicating that stargazin-like mechanisms for targeting AMPA receptors may be widespread in the central nervous system.     

A one-hit model of cell death in inherited neuronal degenerations

In genetic disorders associated with premature neuronal death, symptoms may not appear for years or decades. This delay in clinical onset is often assumed to reflect the occurrence of age-dependent cumulative damage. For example, it has been suggested that oxidative stress disrupts metabolism in neurological degenerative disorders by the cumulative damage of essential macromolecules. A prediction of the cumulative damage hypothesis is that the probability of cell death will increase over time. Here we show in contrast that the kinetics of neuronal death in 12 models of photoreceptor degeneration, hippocampal neurons undergoing excitotoxic cell death, a mouse model of cerebellar degeneration and Parkinson's and Huntington's diseases are all exponential and better explained by mathematical models in which the risk of cell death remains constant or decreases exponentially with age. These kinetics argue against the cumulative damage hypothesis; instead, the time of death of any neuron is random. Our findings are most simply accommodated by a 'one-hit' biochemical model in which mutation imposes a mutant steady state on the neuron and a single event randomly initiates cell death. This model appears to be common to many forms of neurodegeneration and has implications for therapeutic strategies.     

Evasion of the p53 tumour surveillance network by tumour-derived MYC mutants

The c-Myc oncoprotein promotes proliferation and apoptosis, such that mutations that disable apoptotic programmes often cooperate with MYC during tumorigenesis. Here we report that two common mutant MYC alleles derived from human Burkitt's lymphoma uncouple proliferation from apoptosis and, as a result, are more effective than wild-type MYC at promoting B cell lymphomagenesis in mice. Mutant MYC proteins retain their ability to stimulate proliferation and activate p53, but are defective at promoting apoptosis due to a failure to induce the BH3-only protein Bim (a member of the B cell lymphoma 2 (Bcl2) family) and effectively inhibit Bcl2. Disruption of apoptosis through enforced expression of Bcl2, or loss of either Bim or p53 function, enables wild-type MYC to produce lymphomas as efficiently as mutant MYC. These data show how parallel apoptotic pathways act together to suppress MYC-induced transformation, and how mutant MYC proteins, by selectively disabling a p53-independent pathway, enable tumour cells to evade p53 action during lymphomagenesis.     

α-Synuclein蛋白过表达对小鼠纹状体的影响

 帕金森病是世界第二大老年神经退行性疾病,致病机理极为复杂。α-synuclein（α-syn）是帕金森病主要病理特征的路易小体的主要组成成分,其突变基因α-syn A30P 也与部分家族性帕金森相关。通过对过表达野生型人源α-syn WT 及其突变体α-syn A30P 蛋白的转基因小鼠的行为学检验、脑部纹状体中氧化应激水平以及儿茶酚胺异喹啉物质水平的检测,研究过表达α-syn 蛋白对小鼠纹状体产生的影响。结果显示转基因小鼠模型与正常鼠相比,其协调能力明显下降,纹状体与全脑的比例显著降低。同时,模型鼠脑中的氧化应激水平与儿茶酚胺异喹啉物质的表达水平均显著升高。研究结果说明,α-syn 蛋白及其突变体的过表达会引起小鼠脑部纹状体中氧化应激水平与儿茶酚异喹啉物质表达水平的升高,从而导致纹状体组织严重损伤。     

Effects of sense and antisense centromere/kinetochore complex protein-B （CENP-B） in cell cycle regulation

This paper investigates the effects of sense and antisense centromere/kinetochore complex protein-B （CENP-B） in cell cycle regulation. Full-length cenpb cDNA was subcloned into pBI-EGFP eukaryotic expression vector in both sense and antisense orientation. HeLa-Tet-Off cells were transfected with sense or antisense cenpb vectors. Sense transfection of HeLa-Tet-Off cells resulted in the formation of a large centromere/kinetochore complex, and apoptosis of cells following several times of cell division. A stable antisense cenpb transfected cell line, named HACPB, was ob- tained. The centromere/kinetochore complex of HACPB cells became smaller than control HeLa-Tet-Off cells and scattered, and the expression of CENP-B was down-regulated. In addition, delayed cell cycle progression, inhibited malignant phenotype, restrained ability of tumor formation in nude mice, and delayed entry from G2fM phase into next G1 phase were observed in HACPB cells. Furthermore, the expression of cyclin-dependent kinases （CDKs）, cyclins, and CDK inhibitors （CKIs） were modulated during different phases of the cell cycle. CENP-B is an essential protein for the maintenance of the structure and function of centromere/kinetochore complex, and plays important roles in cell cycle regulation.     

细胞周期与细胞凋亡共同的调控分子--Survivin蛋白(综述)

细胞周期与细胞凋亡是有着紧密联系的生命活动。尽管凋亡调控蛋白常常牵涉到细胞周期的调控，但是细胞周期与细胞凋亡共同的的调控分子却很少见。一个新的抗凋亡蛋白——Survivin蛋白，最近被发现同时具有调控细胞凋亡和细胞周期的双重功能，这为细胞周期与细胞凋亡之间存在紧密联系提供了有力的证据。另一方面，它的表达和分布特点对细胞增殖非常有利，提示Survivin蛋白可能是快速增殖细胞(如癌细胞)重要的测控分子。     

饮食限制对学习记忆和抗肿瘤作用的研究进展

对饮食限制在学习记忆和抗肿瘤方面作用的研究进展进行了概述.饮食限制可通过改善大脑海马区的神经细胞、脑源性神经营养因子和降低氧化应激作用等,增强机体的学习记忆能力,预防老年痴呆症.饮食限制可增强机体的抗氧化酶活性,降低胰岛素样生长因子-1(IGF-1)和血糖水平、诱导癌细胞凋亡及抑制肿瘤血管生成等,进而抑制肿瘤的生长,延长机体的寿命.因此,可通过饮食限制提高机体清除自由基的能力,增强机体的免疫力,延缓机体的衰老,抑制肿瘤的发生,预防老年痴呆症.