神经元极性发育分子与细胞机制获揭示

<正>中科院上海生科院神经所蒲慕明研究组研究了神经元的形态建成机制,从而揭示了神经元极性发育的分子与细胞机制。相关成果已在线发表于美国《国家科学院院刊》。此次研究人员发现,通过在体定点注射逆转录病毒操作,在成年小鼠海马齿状回中特异性敲除蛋白激酶LKB1或者过表达激酶失活形式LKB1,都能破坏成年新生颗粒细胞中树突数目的唯一性和树突朝向分子层生长的方向选择性,从而造成树突从颗粒细胞的胞体上多点起     

蓝舌病毒释放机制的研究进展

蓝舌病毒(Bluetongue virus,BTV)作为由媒介昆虫库蠓传播的引起反刍动物蓝舌病(Bluetongue,BT)的病原微生物,同时也是研究无囊膜病毒(Non-enveloped virus)释放机制的经典模型。文中以BTV侵染细胞及组装为始,对BTV诱导细胞自噬并通过多囊泡体以细胞外囊泡形式释放、BTV诱导细胞凋亡而裂解释放、BTV从质膜出芽释放的不同途径以及BTV关键非结构蛋白NS3在调控BTV释放过程中作用机制的研究进展进行综述,为进一步了解BTV感染、增殖、释放的分子机制提供参考。     

Nature揭示染色体复制新机制

在染色体的复制过程中，复制叉前端区域的亲代DNA分子常常会形成正超螺旋。尽管过去的研究证实为了确保复制又向前推进，常通过拓扑异构酶使DNA发生短暂的断裂从而释放出超螺旋产生的应力。还有一些科研团体则认为前进的复制又是沿着DNA螺旋发生旋转进而减少超螺旋的。然而一直以来科学家们对于在真核生物中线性染色体复制诱导的超螺旋应力的释放机制仍了解得不是很清楚。     

神经递质释放过程中的可溶性NSF附着蛋白受体(SNARE)和相关蛋白

近年来,对突触小泡释放神经递质分子机制的研究迅速发展,发现了大量位于神经末梢的蛋白质.它们之间的相互作用与突触小泡释放神经递质相关,特别是位于突触小泡膜上的突触小泡蛋白/突触小泡相关膜蛋白(synaptobrevin/VAMP),位于突触前膜上的syntaxin和突触小体相关蛋白(synaptosome-associated protein of 25 ku),三者聚合形成的可溶性NSF附着蛋白受体(SNARE)核心复合体在突触小泡的胞裂外排、释放递质过程中有重要作用.而一些已知及未知的与SNARE蛋白有相互作用的蛋白质,可通过调节SNARE核心复合体的形成与解离来影响突触小泡的胞裂外排,从而可以调节突触信号传递的效率及强度,在突触可塑性的形成中起重要作用.     

肝再生与线粒体蛋白释放的关系

在肝部分切除或创伤后,残存肝组织很快就进入复杂的再生过程。在肝再生过程中,线粒体发挥着重要的作用,不仅提供能量,而且参与细胞的信号转导等活动。近年来众多研究表明,在肝再生过程中线粒体透性转换有明显特征性的变化,并具有一定的规律性;同时发现,在肝再生早期有一些线粒体基质蛋白释放到胞液中,提示线粒体蛋白的释放可能与肝再生之间具有一定的关系。     

多巴胺释放对纹状体神经元信息编码的影响

运动功能是在神经系统直接或间接调控下协调完成的,基底神经节对于运动功能的执行起至关重要作用,其中纹状体在基底神经节处于中心地位,接受多巴胺能神经元的投射,通过直接、间接通路参与运动的调控。多巴胺能神经元中多巴胺的释放以活性区介导的快速突触传递的方式进行。活性区由Bassoon、RIM和ELKS三种支架蛋白组成,其中RIM蛋白对多巴胺释放起调节作用。纹状体不同类型的神经元电活动随着多巴胺释放含量的变化出现适应性变化。当纹状体去多巴胺支配时,中等多棘神经元和快放电中间神经元放电频率显著增加;当纹状体多巴胺耗竭时,大胆碱能中间神经元出现pause-rebound编码模式。本文对多巴胺运动控制的分子机制展开讨论,并对其在运动疲劳中枢机制中的研究进行综述,为纹状体神经元靶向干预提供理论依据和新思路。     

多巴胺调节海马神经元可塑性的研究进展

多巴胺是脑内重要的信息传递物质,不仅可以作为递质释放到前额叶、伏隔核等脑区,直接进行信息传递,也可以作为调质调节其它突触递质的传递,并影响神经元可塑性。海马参与构成边缘系统,受多巴胺能神经支配,执行着有关学习记忆以及空间定位的功能。海马神经元的可塑性是学习记忆的细胞分子基础。研究表明,多巴胺对海马神经元的突触可塑性和兴奋性可塑性都具有重要的调节作用。本文扼要综述多巴胺对海马神经元突触可塑性和兴奋性可塑性的调节机制的研究进展,以期为DA系统参与海马区学习记忆功能的研究提供新思路,更深入地了解学习记忆的神经机制。     

脊髓胶状质内生长抑素免疫反应阳性结构与一级传入纤维之间的突触连接

本文用单纯免疫电镜及免疫电镜与溃变(后根切断术)相结合的方法,研究了一级传入纤维与脊髓胶状质内生长抑素(SOM)阳性结构之间的突触连结。结果在脊髓胶状质内观察到SOM阳性的胞体、轴突、树突及溃变的轴突,以上结构间形成了几种不同类型的突触连结:(1)Ⅰ型或Ⅱ型突触球的中央成份(CⅠ或CⅡ末梢)是溃变的或是SOM免疫反应阳性的,它们与周围的树突形成轴树突触、轴轴突触或树轴突触,其中有一些周围的树突还是SOM阳性的。(2)某些简单的轴突(不参与构成突触球的轴突)呈暗型溃变,并与SOM阳性的树突形成轴树突触。(3)简单的SOM阳性的致密型轴突与含SOM的树突或核周质形成轴树或轴体突触。(4)简单的SOM阳性的亮型轴突与含SOM的树突形成轴树突触。这些突触关系提示脊髓胶状质内SOM阳性树突和胞体可直接从一级传入纤维或脊髓后角固有神经元接受冲动,其中有一些一级传入纤维和脊髓后角固有神经元也是SOM阳性的。这表明在脊髓固有神经元与一级传入纤维之间及脊髓固有神经元本身都存在着自调节突触。本实验结果为SOM参与感觉信息的调节提供了超微结构证据。     

肽链释放因子识别终止密码子的机制

肽链释放因子(polypeptide release factor, RF)是参与细胞内蛋白质合成终止过程中新生肽链释放的一组重要的蛋白质,包括两类,即第一类肽链释放因子(classⅠrelease factor, RFⅠ)和第二类肽链释放因子(classⅡrelease factor, RFⅡ).关于第一类肽链释放因子识别终止密码子的机制和功能位点是目前分子细胞生物学领域的一个研究热点,第二类肽链释放因子作为一类GTP酶,在第一类肽链释放因子识别终止密码子和肽链释放过程中的协同作用也备受关注.近些年来,通过构建体内和体外的测活体系,对第一类肽链释放因子识别终止密码子的机制的研究取得了一些进展,提出了多种假说和模型,尤其是对第一类肽链释放因子的晶体结构及两类肽链释放因子复合体的空间结构的研究,为揭示真核生物细胞内蛋白质合成终止机制提供了直接的证据.     

分子发动机研究进展

分子发动机是利用化学能/化学势进行机械作功的生物大分子,包括线性分子发动机与旋转式分子发动机两大类.它们参与了胞质运输、DNA复制、基因转录、ATP合成／水解等一系列重要生命活动过程.目前对于各种分子发动机的结构及作用机制的研究取得了一些重要进展.     

In vivo release of transmitters in the cat basal ganglia

The release of transmitters was studied in various structures of the basal ganglia in cats implanted with several push-pull cannulas. Local depolarization enhanced Met-enkephalin release in the globus pallidus. Activation of striatonigral substance P(SP) neutrons stimulated the transmitter release from terminals. Unilateral electrical stimulation of the caudate nucleus evoked GABA release in both substantia nigrae and pallidoentopeduncular nuclei. The unilateral facilitation or interruption of nigral SP transmission modified dopamine (DA) release in the ipsilateral caudate nucleus in contrast, modifications of GABAergic or glycinergic nigral transmissions induced bilateral symmetrical effects, whereas bilateral asymmetrical changes in DA release in the two caudate nuclei were seen during the unilateral modification of nigral DA transmission. Changes in the dendritic release of DA induced changes in serotonin release both in the substantia nigra and in the ipsilateral caudate nucleus. Finally, it will be shown that acetylcholinesterase can be released from the substantia nigra and the caudate nucleus through processes dependent on nerve activity.     

The D3 dopamine receptor inhibits dopamine release in PC-12/hD3 cells by autoreceptor signaling via PP-2B, CK1, and Cdk-5

The function of the D₃ dopamine (DA) receptor remains ambiguous largely because of the lack of selective D₃ receptor ligands. To investigate the function and intracellular signaling of D₃ receptors, we established a PC‐12/hD3 clone, which expresses the human D₃ DA receptor in a DA producing cell line. In this model, we find that the D₃ receptor functions as an autoreceptor controlling neurotransmitter secretion. Pre‐treatment with 3,6a,11, 14‐tetrahydro‐9‐methoxy‐2 methyl‐(12H)‐isoquino[1,2‐b] pyrrolo[3,2‐f][1,3] benzoxanzine‐1‐carboxylic acid, a D₃ receptor preferring agonist, dose‐dependently suppressed K⁺‐evoked [³H]DA release in PC‐12/hD3 cells but not in the control cell line. This effect was prevented by D₃ receptor preferring antagonists GR103691 and SB277011‐A. Furthermore, activation of D₃ receptors significantly inhibits forskolin‐induced cAMP accumulation and leads to transient increases in phosphorylation of cyclin‐dependent kinase 5 (Cdk5), dopamine and cAMP‐regulated phosphoprotein of M_r 32 000 and Akt. Because we observed differences in Cdk5 phosphorylation as well as Akt phosphorylation after DA stimulation, we probed the ability of Cdk5 and phosphatidylinositol‐3 kinase (PI3K) to influence DA release. Cdk5 inhibitors, roscovitine, or olomoucine, but not the PI3K inhibitor wortmannin, blocked the D₃ receptor inhibition of DA release. In a complimentary experiment, over‐expression of Cdk5 potentiated D₃ receptor suppression of DA release. Pertussis toxin, 3‐[(2,4,6‐trimethoxyphenyl)methylidenyl]‐indolin‐2‐one and cyclosporine A also attenuated D₃ receptor‐mediated inhibition of DA release indicating that this phenomenon acts through Gi/oα and casein kinase 1, and phosphatase protein phosphatase 2B (calcineurin), respectively. In support of previous data that D₃ DA receptors reduce transmitter release from nerve terminals, the current results demonstrate that D₃ DA receptors function as autoreceptors to inhibit DA release and that a signaling pathway involving Cdk5 is essential to this regulation.     

Somatodendritic dopamine release: recent mechanistic insights

Dopamine (DA) is a key transmitter in motor, reward and cogitative pathways, with DA dysfunction implicated in disorders including Parkinson''s disease and addiction. Located in midbrain, DA neurons of the substantia nigra pars compacta project via the medial forebrain bundle to the dorsal striatum (caudate putamen), and DA neurons in the adjacent ventral tegmental area project to the ventral striatum (nucleus accumbens) and prefrontal cortex. In addition to classical vesicular release from axons, midbrain DA neurons exhibit DA release from their cell bodies and dendrites. Somatodendritic DA release leads to activation of D2 DA autoreceptors on DA neurons that inhibit their firing via G-protein-coupled inwardly rectifying K⁺ channels. This helps determine patterns of DA signalling at distant axonal release sites. Somatodendritically released DA also acts via volume transmission to extrasynaptic receptors that modulate local transmitter release and neuronal activity in the midbrain. Thus, somatodendritic release is a pivotal intrinsic feature of DA neurons that must be well defined in order to fully understand the physiology and pathophysiology of DA pathways. Here, we review recent mechanistic aspects of somatodendritic DA release, with particular emphasis on the Ca²⁺ dependence of release and the potential role of exocytotic proteins.     

Dopamine and dopamine receptors as target sites for cardiovascular drug action

It is controversial whether dopamine (DA) is a peripheral neurotransmitter in the cardiovascular/renal system. The endogenous concentration of DA in the heart and blood vessels is generally only a fraction (5%) of that of norepinephrine (NE). With perhaps the exception of the kidney, the majority of the evidence suggests a precursor role for this amine rather than that of a neurotransmitter. The main weakness of arguments favoring DA as a vascular neurotransmitter is relative lack of data showing selective DA release and lack of effects of selective DA antagonists on neural stimulation. However, DA receptors have been characterized in cardiovascular tissues and are of two types: DA1 receptors located on vascular smooth muscle (postjunctional), which appear to mediate relaxation of the muscle, and DA2 receptors located on sympathetic nerves (pejunctional), which inhibit NE release. These receptors are interesting and potential target sites for novel cardiovascular drug action for the treatment of hypertension and renal ischemia. Moreover, selective DA receptor agonists will be important tools in understanding the role of DA receptors in normal and disease states.     

Control of dendritic development by the Drosophila fragile X-related gene involves the small GTPase Rac1

Fragile X syndrome is caused by loss-of-function mutations in the fragile X mental retardation 1 gene. How these mutations affect neuronal development and function remains largely elusive. We generated specific point mutations or small deletions in the Drosophila fragile X-related (Fmr1) gene and examined the roles of Fmr1 in dendritic development of dendritic arborization (DA) neurons in Drosophila larvae. We found that Fmr1 could be detected in the cell bodies and proximal dendrites of DA neurons and that Fmr1 loss-of-function mutations increased the number of higher-order dendritic branches. Conversely, overexpression of Fmr1 in DA neurons dramatically decreased dendritic branching. In dissecting the mechanisms underlying Fmr1 function in dendrite development, we found that the mRNA encoding small GTPase Rac1 was present in the Fmr1-messenger ribonucleoprotein complexes in vivo. Mosaic analysis with a repressor cell marker (MARCM) and overexpression studies revealed that Rac1 has a cell-autonomous function in promoting dendritic branching of DA neurons. Furthermore, Fmr1 and Rac1 genetically interact with each other in controlling the formation of fine dendritic branches. These findings demonstrate that Fmr1 affects dendritic development and that Rac1 is partially responsible for mediating this effect.     

Direct and indirect presynaptic control of dopamine release by excitatory amino acids

Summary Dopamine (DA) release from nerve terminals of the nigrostriatal DA neurons not only depends on the activity of nigral DA cells but also on presynaptic regulation. Glutamatergie neurons of cortical origin play a prominent role in these presynaptic regulations. The direct glutamatergic presynaptic control of DA release is mediated by N-methyl-D-aspartate (NMDA) and-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionate (AMPA) receptors, located on DA nerve terminals. In addition, by acting on striatal target cells, these glutamatergic neurons contribute also to indirect regulations of DA release involving several transmitters such as GABA, acetylcholine and neuropeptides. Diffusible messengers such as nitric oxide (NO) or arachidonic acid (AA) which are particularly formed under the stimulation of NMDA receptors may also participate to the regulation of DA release. In the present study, it will be shown that the co-application of NMDA and carbachol synergistically increases the release of [³H]-DA and that this effect is reduced by mepacrine or 4-bromophenacylbromide (10⁷M), two inhibitors of PLA2. Therefore endogenously released AA induced by the co-stimulation of NMDA and cholinergic receptors seems to be involved, at least partly, in the release of DA.     

Good riddance to dopamine: Roles for the dopamine transporter in synaptic function and dopamine-associated brain disorders

The neurotransmitter dopamine (DA) plays a critical role in CNS circuits that provide for attention, executive function, reward responses, motivation and movement. DA is inactivated by the cocaine- and amphetamine-sensitive DA transporter (DAT), a protein that also provides a pathway for non-vesicular DA release. After a brief review of DAT function and psychostimulant actions, we consider the importance DAT in relation to the distinct firing patterns of DA neurons that permit awareness of novelty and reward. Finally, we review recent efforts to gather direct support for DAT-linked disorders, with a specific focus on DAT mutations recently identified in subjects with ADHD.     

Chemical neuroprotection in the cochlea: the modulation of dopamine release from lateral olivocochlear efferents

The prevalence of sensorineural hearing loss is increasing worldwide, mainly due to ageing, increased noise exposure and cardiovascular risk factors. Several papers dealt with the mechanisms underlying the primary causes of impaired hearing and eventual deafness, including the damage and loss of auditory hair cells; however, very little is known about the protective mechanisms that exist for hearing. Several recent investigations have implicated dopamine (DA) in a neuroprotective circuit for the cochlea. The lateral olivocochlear (LOC) efferents provide axonal innervation of the inner hair cell afferent synapses and release DA and other substances in response to different stimuli. Under ischemic conditions or during noise exposure, DA has been proven to play a neuroprotective role against glutamate excitotoxicity. This review summarises what is currently known about the modulation of DA release in the cochlea, using primarily in vitro experimental data. Based on recent knowledge, there could be two functional subgroups within the LOC fibres, i.e., the DA- and GABA-containing projections. In this review, we attempt to show the neurochemical interactions between these two subsystems. Other aspects of cochlear neurotransmission are also discussed to provide a complete picture of cochlear dopaminergic function in physiological and pathophysiological cases with particular reference to excitotoxicity.     

Helper T cells, dendritic cells and CTL Immunity

In this review, we examine the emerging view that all CTL responses depend on CD4 T-cell help for the generation of efficient memory. We further review the evidence that CD4 and CD8 T cells must recognize antigen on the same dendritic cell, and examine why this corecognition is required. Earlier studies have suggested that CD4 T cells must activate the dendritic cell via CD40 to license it for the capacity to prime CTL immunity. More recently, however, CD40 signalling of the CTL has been reported. Here, we argue that the main reason for corecognition of antigen on the dendritic cell may be related to the time taken to activate and release CD4 and CD8 T cells from their priming dendritic cell. CD4 T cells may only be capable of activating one dendritic cell during the period that CD8 T cells are primed. In this case, corecognition of this same dendritic cell would be essential.     

Morphological analysis of Drosophila larval peripheral sensory neuron dendrites and axons using genetic mosaics

Nervous system development requires the correct specification of neuron position and identity, followed by accurate neuron class-specific dendritic development and axonal wiring. Recently the dendritic arborization (DA) sensory neurons of the Drosophila larval peripheral nervous system (PNS) have become powerful genetic models in which to elucidate both general and class-specific mechanisms of neuron differentiation. There are four main DA neuron classes (I-IV)(1). They are named in order of increasing dendrite arbor complexity, and have class-specific differences in the genetic control of their differentiation(2-10). The DA sensory system is a practical model to investigate the molecular mechanisms behind the control of dendritic morphology(11-13) because: 1) it can take advantage of the powerful genetic tools available in the fruit fly, 2) the DA neuron dendrite arbor spreads out in only 2 dimensions beneath an optically clear larval cuticle making it easy to visualize with high resolution in vivo, 3) the class-specific diversity in dendritic morphology facilitates a comparative analysis to find key elements controlling the formation of simple vs. highly branched dendritic trees, and 4) dendritic arbor stereotypical shapes of different DA neurons facilitate morphometric statistical analyses. DA neuron activity modifies the output of a larval locomotion central pattern generator(14-16). The different DA neuron classes have distinct sensory modalities, and their activation elicits different behavioral responses(14,16-20). Furthermore different classes send axonal projections stereotypically into the Drosophila larval central nervous system in the ventral nerve cord (VNC)(21). These projections terminate with topographic representations of both DA neuron sensory modality and the position in the body wall of the dendritic field(7,22,23). Hence examination of DA axonal projections can be used to elucidate mechanisms underlying topographic mapping(7,22,23), as well as the wiring of a simple circuit modulating larval locomotion(14-17). We present here a practical guide to generate and analyze genetic mosaics(24) marking DA neurons via MARCM (Mosaic Analysis with a Repressible Cell Marker)(1,10,25) and Flp-out(22,26,27) techniques (summarized in Fig. 1).