NEURAL REGENERATION RESEARCH
Volume 7, Issue 11, April 2012
Cite this article as: Neural Regen Res. 2012;7(11):842-848.
842 Maoguang Yang☆, Studying for doctorate, Department of Orthopedics, China-Japan Union Hospital, Jilin University, Changchun 130033, Jilin Province, China Corresponding author: Xiaoyu Yang, Professor, Doctoral supervisor, Department of Orthopedics, China-Japan Union Hospital, Jilin University, Changchun 130033, Jilin Province, China; Xingwei Duan, M.D., Working in People’s Hospital of Shenzhen Baoan District yangxiaoyu88@https://www.doczj.com/doc/e98661426.html, Received: 2012-02-07 Accepted: 2012-03-08
(N20111212001/WJ)
Yang MG, Wu MF, Xia P, Wang CX, Yan Peng , Gao Q, Liu J, Wang HT, Duan XW, Yang XY. The role of microtubule- associated protein 1B in axonal growth and neuronal migration in the central nervous system. Neural Regen Res.
2012;7(11):842-848.
https://www.doczj.com/doc/e98661426.html,
https://www.doczj.com/doc/e98661426.html,
doi:10.3969/j.issn.1673-5374. 2012.11.008
The role of microtubule-associated protein 1B in axonal growth and neuronal migration in the central nervous system*☆
Maoguang Yang, Minfei Wu, Peng Xia, Chunxin Wang, Peng Yan, Qi Gao, Jian Liu, Haitao Wang, Xingwei Duan, Xiaoyu Yang
Department of Orthopedics, China-Japan Union Hospital, Jilin University, Changchun 130033, Jilin Province, China Abstract
In this review, we discuss the role of microtubule-associated protein 1B (MAP1B) and its
phosphorylation in axonal development and regeneration in the central nervous system. MAP1B
exhibits similar functions during axonal development and regeneration. MAP1B and phosphorylated
MAP1B in neurons and axons maintain a dynamic balance between cytoskeletal components, and
regulate the stability and interaction of microtubules and actin to promote axonal growth, neural
connectivity and regeneration in the central nervous system.
Key Words: microtubule-associated protein 1B; central nervous system; axonal regeneration;
axonal development; axon guidance; neuronal migration
Abbreviations: CNS, central nervous system; MAP1B, microtubule-associated protein 1B; GSK3β,
glycogen synthase kinase 3β; PI3K, phosphatidylinositol-3 kinase; JNK, c-Jun N-terminal kinase
INTRODUCTION
Although recent evidence indicates that axonal regeneration and neural pathway reconstruction can occur following central nervous system (CNS) injury, brain and spinal axons cannot rapidly or effectively traverse the site of injury. Glial scar formation, in particular, hinders axonal regeneration and CNS self-repair[1]. Consequently, trauma, ischemia and degenerative disease can result in permanent and severe disability. Microtubule-associated protein 1B (MAP1B) is one of the first MAPs expressed in neuroblasts, and is essential for axonal development and regeneration. It can induce cytoskeletal rearrangements by regulating actin and microtubule dynamics, and promote axonal growth, development, branching and regeneration[2-3]. Moreover, it plays an important role in axon guidance and neuronal migration[4].
A variety of signaling molecules are associated with axonal development and regeneration or axonal guidance, such as netrins[5], neurotrophic factor[6-7] and Wnt[8], and signaling molecules associated with neuronal migration, such as Reelin[9], modulate MAP1
B function. However, the signaling pathways that regulate MAP1B function and the underlying molecular mechanisms remain poorly understood. Here, we review recent advances in our
understanding of MAP1B function and
regulation. An appreciation of the underlying
molecular mechanisms should help
researchers in their efforts to promote CNS
repair and axonal regeneration, and lead to
effective methods for neurological functional
recovery following CNS injury.
MAP1B
MAP1B is a high-molecular-weight protein.
The precursor polypeptide undergoes
proteolytic processing to generate the
C-terminal-derived light chain and the
N-terminal-derived heavy chain[10]. The
C-terminal product is a small protein, called
MAP1B light chain 1[10], which contains a
microtubule and actin binding domain and
can regulate interactions between
microtubules and microfilaments[11]. The
MAP1B heavy chain contains a
microtubule-binding domain and mediates
binding of MAP1B light chain 1 to
microtubules[12]. Cueille et al [13] found that
the MAP1B heavy chain binds actin and
regulates interactions between microtubules
and actin. This indicates that MAP1B can
regulate microtubule stability, interactions
between microtubules and actin, and axonal
extension[14]. MAP1B heavy chain is mainly
involved in axonal longitudinal growth,
microtubule stability and local actin
dynamics, while MAP1B light chain 1 may
https://www.doczj.com/doc/e98661426.html,
enhance growth cone dynamics by providing nodes for F-actin assembly[13].
Protein bioactivity and distribution vary with
post-translational modification. MAP1B contains at least 33 phosphorylation sites[15], and differential phosphorylation modulates function. Phosphorylated MAP1B is categorized as type I or type II, i.e. P1-MAP1B or P2-MAP1B. The balance between MAP1B and phosphorylated MAP1B is regulated by protein kinases and protein phosphatases. P1-MAP1B is generated by phosphorylation by various protein kinases, such as glycogen synthase kinas e 3β (GSK3β) and
cyclin-dependent kinase 5. Dephosphorylation of
P1-MAP1B is controlled by protein phosphatase 2A and 2B. P2-MAP1B is generated by phosphorylation by casein kinase. It is dephosphorylated by protein phosphatase 1 and 2A[16-17].
The functions and subcellular distributions of P1-MAP1B and P2-MAP1B are different. P1-MAP1B mainly aggregates in distal axons and growth cones during neural development to respond to extracellular factors. It regulates microtubule and actin dynamics and axonal extension[18]. P1-MAP1B gradually disappears following axonal maturation, and is used as a marker of axonal growth[19]. P2-MAP1B is mainly localized in subcellular structures of neurons throughout postnatal development[20]
MAP1B AND AXONAL DEVELOPMENT Proteomics shows that MAP1B accumulates in the growth cone during axonal development to a greater extent than in elongating axons[18, 21]. In addition, inhibiting MAP1B function significantly slows axonal development, indicating the importance of MAP1B in axonogenesis and elongation. Cultured neurons from a mouse line deficient in MAP1B showed that axonal elongation was significantly reduced, indicating inhibition of MAP1B function can partly suppress axonal growth[22], consistent with another study[23] showing that other MAPs also promote axonogenesis. Knockout of MAP1B and MAP2 or MAP1B and tau significantly impairs axonal sprouting, but knockout of MAP2 and tau does not[24-25], suggesting that although the functions of the various MAP family members partly overlap, MAP2 and tau cannot replace MAP1B in axonal development. The quantity of MAP1B in neurons is tightly controlled, because low or high MAP1B levels can result in delayed axonal sprouting, pathological axonogenesis and reduced axonal growth[26-27].
MAP1B contains microtubule and actin binding domains; thus, it can regulate microtubule and actin stability[11-13]. Neuronal cultures from MAP1B knockout mice exhibit delayed neuronal migration and suppressed neurite elongation, but microtubule extension into growth cones is increased[24, 28]. Inhibiting MAP1B phosphorylation increases the size of growth cones and leads to shortened and thickened axons[29]. These results indicate that MAP1B can stabilize microtubules and induce the formation of microfilaments.
Immunodepletion of MAP1B significantly increases the sensitivity of microtubules in the distal axon and growth cone to nocodazole-induced depolymerization[23, 29], indicating that MAP1B increases the ability of microtubules to resist depolymerization. This may be related to the ability of MAP1B to induce microtubule protein acetylation and reduce levels of tyrosinated microtubules, thereby increasing microtubule
stability[30-31]. In addition, MAP1B has been shown to regulate growth cone guidance and inhibit branching of regenerating axons[3], but Kuo et al [2] demonstrated that axonal branching is increased following MAP1B depletion.
MAP1B in distal axons and growth cones can interact with tubulin-tyrosine ligase to promote microtubule tyrosination and regulate microtubule dynamics, but MAP1B phosphorylation does not affect this
interaction[32]. MAP1B binding to dynamic microtubules increases axonal elongation[33]. MAP1B cannot induce microtubule tyrosination because the tubulin-tyrosine ligase binding site is shielded[32]. These results indicate that MAP1B function depends on its location along the axon. MAP1B in axon terminals and growth cones promotes microtubule tyrosination, thereby regulating microtubule dynamics and stimulating axonal elongation. In contrast, MAP1B at other sites along the axon primarily stabilizes microtubules and prevents microtubule depolymerization.
Previous studies have shown that axons are thickened and shortened, and growth cone extension is increased following inhibition of MAP1B phosphorylation, while deletion of MAP1B or increasing the MAP1B/P-MAP1B ratio increases microtubule stability[28-29]. Moreover, phosphorylated MAP1B mainly regulates microtubule dynamics in growth cones and growing axons[29, 34], indicating that it contributes to microtubule stability and dynamics and plays an important role in regulating microtubule stability, because extensive promotion or inhibition of microtubule stability can affect axonal growth and development[35]. Microtubules and the associated MAP1B extend into growth cones, and microtubules within the growth cone can bind actin[33]. This indirectly indicates that MAP1B binds actin, thereby regulating the interaction between microtubules and actin. Phosphorylated MAP1B can enhance growth cone motility by regulating actin dynamics in the growth
cone[28]. In the initial stage of axonogenesis, phosphorylated MAP1B is at very low levels, but its levels increase with axonal development and elongation[36]. P1-MAP1B levels are highest in the growth cone, where it binds axonal terminal microtubules[27, 37]. There, it primarily regulates axonal elongation by modulating microtubule dynamics and interactions between microtubules and actin[23, 35, 38]. P2-MAP1B also participates in dendrite and synapse formation[14].
GSK3β phosphorylates MAP1B to regulate microtubule
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dynamics[29, 39]. Nerve growth factor in primary neurons promotes axonal growth through the GSK3β-MAP1B pathway[6, 40]. Nerve growth factor interacts with tropomyosin-related tyrosine kinase to activate the mitogen-activated protein kinase/extracellular regulated kinase pathway, which in turn indirectly stimulates
GSK3β phosphorylation through other kinases[7]. Other proteins, such as dystroglycan, can also interact with MAP1B and modulate GSK3β-mediated MAP1B phosphorylation[41]. GSK3β-mediated MAP1B phosphorylation results in microtubule sensitivity to depolymerization and increases the quantity of unstable microtubules[42], thereby promoting axonal elongation[19]. Reduced MAP1B phosphorylation by inhibiting G SK3β activity through the Wnt pathway thickens and shortens axons, and enlarges growth cones and stabilizes microtubules[8].
Nerve growth factor activates phosphatidylinositol-3 kinase (PI3K) and induces GSK3β phosphorylation at ser-9, which blocks the abi lity of GSK3β to activate primed substrate, i.e. substrate that is
pre-phosphorylated at certain residues[40, 43]. Two types of GSK3β phosphorylation sites, primed and non-primed, are found in MAP1B[34, 44]. Therefore, nerve growth factor can negatively regulate P1-MAP1B following PI3K activation, i.e. nerve growth factor can regulate
P1-MAP1B levels through the MAPK and PI3K pathways.
In PC12 cells, nerve growth factor activates
neuron-specific p35 by activating the MAPK-ERK1/2 pathway. Subsequently, p35 binds Cdk5 to form an active complex that phosphorylates MAP1B to generate
P1-MAP1B[45]. Cdk5 is distributed throughout the cytoplasm and axons, while p35 is only found in axon terminals and growth cones[46]. Therefore, Cdk5 can only be activated in axon terminals and growth cones, possibly contributing to the large amount of P1-MAP1B at these sites[27, 37], which plays crucial roles in microtubule dynamics, axonal elongation and growth cone guidance[46].
The c-Jun N-terminal kinase (JNK) phosphorylates a variety of cytoskeletal proteins, including MAP1B and MAP2. Blocking the JNK pathway reduces MAP1B phosphorylation[47-49], resulting in axonal degeneration and cytoskeletal defects. Moreover, JNK in certain neuronal cell types can promote axonal sprouting[47]. Tanner et al[50] reported that MAP1B may also regulate interactions between the cytoskeleton and the cell membrane, and between the cytoskeleton and the extracellular matrix or adhesion molecules. During synaptogenesis at the end stage of axonal development, MAP1B promotes axonal development through three pathways: (1) MAP1B promotes membrane skeleton assembly through interactions with F-actin; (2) MAP1B interacts with phospholipids; (3) MAP1B crosses the plasma membrane and functions as a type I membrane protein[51-52]. At least one form of MAP1B located at presynaptic and postsynaptic regions has been demonstrated to interact with cell membranes and synapsin, contributing to synapse formation and function in the later stages of axonal development[53]. The responsible subtype may be P2-MAP1B. However, this hypothesis requires further investigation.
MAP1B AND AXONAL REGENERATION
CNS functional recovery mainly depends on axonal regeneration and reconstruction of neural circuitry. The injured corticospinal tract forms new connections with spinal neurons, which aids neurological functional recovery to an extent[1]. Peripheral nerve injury can induce sprouting of dorsal root ganglia into the posterior horn[54]. These results indicate that the CNS internal environment supports axonal regeneration.
MAP1B mRNA and protein expression are significantly increased in cortical infarct foci and surrounding regions, promoting sensory and motor functional recovery[55-56]. This indicates that MAP1B plays an important role in nervous system repair. MAP1B can regulate interactions between microtubules and actin[23, 35, 38], and microtubules aggregate only in the presence of
MAP1B[57-58]. Cueille et al[13] proposed that interactions between microtubules and actin play important roles not only in neurogenesis and differentiation, but also in axonal regeneration and neuronal connectivity in adults, indicating that MAP1B promotes axonal regeneration by regulating interactions between microtubules and actin and that high expression of MAP1B in the CNS contributes to neural plasticity.
Similar to axonal development, the ability of MAP1B to promote axonal regeneration and neuronal connectivity are highly correlated with MAP1B phosphorylation. Following traumatic brain injury, MAP1B and phosphorylated MAP1B exhibit a brief period of high expression in the hippocampus, cortex and thalamus, which has been demonstrated to associate with cytoskeletal protein stability[37]. Soares et al[59] reported that levels of phosphorylated MAP1B rapidly increase in newly generated axons near the spinal cord lesion, and neurons highly express phosphorylated MAP1B in the spinal cord following injury and periphery nerve injury, which promotes axonal reconstruction. P1-MAP1B and P2-MAP1B have distinct functions during axonal regeneration. Upregulated P1-MAP1B expression is associated with axonal regeneration, and upregulated
P2-MAP1B expression is associated with synaptic plasticity after injury[60].
MAP1B and phosphorylated MAP1B are associated with axonal regeneration in the mature CNS. The JNK pathway has been shown to play an important role in axonal regeneration in JNK gene-deficient mice[61]. Phosphorylated JNK aggregates in distal axons during axonal regeneration, and promotes microtubule elongation and axonal sprouting by inducing MAP1B phosphorylation. Following spinal cord injury, JNK pathway activity is increased, which promotes axonal
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sprouting and regeneration associated with MAP1B phosphorylation[59].
Similar to processes in axonal development, the JNK pathway can catalyze MAP1B phosphorylation during axonal regeneration. However, the correlation between CNS axonal regeneration and development, and the precise roles of MAP1B and phosphorylated MAP1B in CNS axonal generation and functional recovery require further investigation.
ROLE OF MAP1B IN AXONAL GUIDANCE During axonal growth, the growth cone is responsible for signal perception and directing axon elongation. Microtubule and actin dynamics are important for growth cone directional motility[62]. Actin is regarded as the main skeletal component for growth cone genesis and guidance, but studies have demonstrated that dynamic microtubules surrounding the growth cone play a major role in regulating growth cone guidance[63-64]. The growth cone responds to the axon guidance factor Netrin-1 and other extracellular guidance cues by transducing these signals into changes in microtubule structure[62], and microtubule stability and growth is the structural basis of axon guidance. Buck et al[62] demonstrated that changes in local microtubular stability, growth and polymerization/depolymerization mediate growth cone navigation. Therefore, microtubular instability is essential for axon and growth cone guidance[65]. The regulation of microtubule dynamics and microtubule and actin interactions allows MAP1B to mediate growth cone migration, which is related to the netrin signaling pathway[4, 66]. MAP1B deletion can increase lateral branch sprouting and perturb growth cone guidance[3, 22, 24]. Netrin-1 is an important guidance molecule and induces intracellular signaling cascades by binding receptor deleted in colorectal cancer[63-64]. MAP1B is involved in Netrin-1 signal transduction[5]. Netrin-1 can enhance MAP1B expression through Cdk5 and Gsk3[5], and it can deactivate phosphorylated MAP1B in growth cones, resulting in impaired growth cone guidance[66].
MAP1B regulates microtubule stability and promotes axon elongation. P1-MAP1B mediates axon elongation to facilitate the formation of neural connections with target tissues or organs. Therefore, MAP1B and
P1-MAP1B maintain microtubule dynamic balance and regulate subcellular distribution to promote axonal growth and guide migration.
MAP1B AND NEURONAL MIGRATION
MAP1B can also guide neuronal migration. Similar to its role in axon guidance, MAP1B regulates neuronal migration[9], and the dynamic balance between MAP1B and P1-MAP1B regulates neuronal morphology and promotes neuronal directional movement.
MAP1B gene defects result in delayed neuronal migration, ectopic localization, cortical plate defects and abnormal CNS development[24], indicating that the protein is involved in axonal elongation and neuronal migration, which is associated with actin and microtubule dynamics[24]. During neuronal migration, MAP1B regulates interactions between actin and microtubules[65]. CNS neuronal migration depends on the dynamic balance between stable and dynamic microtubules[26], which is mediated by MAP1B and
P1-MAP1B[32, 67].
MAP1B can induce dynein, a protein involved in cell migration, to bind lissencephaly-related protein 1[68]. Deletion of MAP1B can attenuate their interaction, indicating the important role of MAP1B in neuronal migration[68]. Bouquet et al [3, 65] proposed that MAP1B exerted similar effects through related mechanisms in different types of cells (Figure 1).
Reelin may promote nervous system development through phosphorylation of MAP1B and other MAPs (such as lissencephaly-related protein 1)[68]. Reelin is an extracellular matrix protein that regulates neuronal migration and localization in the CNS by modulating MAP1B function. Reelin induces disabled 1 phosphorylation through very low density lipoprotein receptor and apolipoprotein receptor 2. Activated disabled 1 activates GSK3 and Cdk5, which synergistically increase levels of P1-MAP1B. The PI3K pathway regulates P1-MAP1B levels by inhibiting GSK3 activity[9, 43] to maintain microtubular instability and promote neuronal migration[9, 35].
Netrin-1 stimulates MAP1B phosphorylation by activating GSK3β and Cdk5 to produce P1-MAP1B, which regulates interaction of microtubules and actin, to mediate neuronal migration[5]. In addition, Netrin-1 interacts with its receptor, deleted in colorectal cancer, to activate the Rho GTPase Rac1[69]. Rac1 regulates MAP1B activity and indirectly controls microtubule dynamics and cell migration[38]. This also demonstrates that Netrin-1 can regulate neuronal migration through MAP1B. Thus, the Netrin-1-Rac1-GSK3β/Cdk5-
MAP1B pathway may be an effective means of controlling neuronal migration, but this idea requires verification.
Kawauchi et al [67] reported that the T-cell lymphoma invasion and metastasis 1 (TIAM1)-Rac1-JNK pathway plays an important role in neuronal migration. TIAM1 activates Rac1 and stimulates neuronal migration by regulating actin cytoskeleton dynamics, and JNK regulates microtubule dynamics by stimulating MAP1B phosphorylation to control neuronal migration[67]. Rac1 regulates MAP1B activity, and MAP1B enhances Rac1 activity by interacting with TIAM1[38, 52]. The effects of Cdk5, GSK3β and JNK on microtubule dynamics must be tightly regulated to maintain the balance between microtubule stability and instability. Otherwise, cytoskeletal dynamics would be impaired, perturbing neuronal migration[9, 35]. Therefore, Reelin[68] and
Netrin-1[5] play important roles in neuronal migration through effects on MAP1B.
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CONCLUSION
MAP1B and phosphorylated MAP1B maintain dynamic balance in CNS neurons and axons. They regulate microtubule stability and dynamics, maintain balance between microtubules and actin, and control their interaction to promote axonal growth, connectivity, and regeneration post-injury. Further studies are needed on MAP1B to investigate treatments to rapidly and effectively ameliorate CNS injury and improve the quality of patient’s life.
Funding:This work was supported by the National Natural Science Foundation of China (Establishment of corticospinal tract ischemic injury model in goat and axonal guidance of microtubule-associated protein 1B in bone marrow-derived mesenchymal stem cells migration in the spinal cord), No. 30972153.
Author contributions:Maoguang Yang conceived and designed the study and wrote the manuscript. Jian Liu contributed to data support. Minfei Wu, Xingwei Duan, Haitao Wang, Peng Xia, Chunxin Wang, Qi Gao and Peng Yan provided and integrated experimental data. Xiaoyu Yang revised the manuscript and was in charge of funds.
Conflicts of interest: None declared. REFERENCES
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(Edited by Yang XY, Zhang YW/Su LL/Song LP)
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神经元轴突标志物
Tau: Neuro n Type of MAP; helps main tai n structure of the axon 神经元树突标志物Drebrin、MAP SAP102 微管相关蛋白Microtubule-associated protein-2(MAP-2) : Neuron Den drite-specific MAP;prote in found specifically in den dritic branching of neuron 是组成神经元细胞骨架的重要组成成分，包括：MAP5 MAP1.2和MAP1 三种不同类型。在神经系统发育、形成和再生过程的不同时期扮演着重要的角色。其中MAP5为早期微观相关蛋白，在胚胎期和新生动物大脑中有较高表达，并随大脑的逐渐成熟而退化，对神经元突起的生长具有重要的引导作用。MAP2包括三种亚型：MAP2a MAP2I和MAP2c其中MAP21和MAP2(出现较早。随着年龄的增长MAP2被组织蛋白酶D所降解，在不同类型的神经元中表达量存在差异。 神经元早期标志物Tubulin、b-4 tubulin : Neuron Important structural protein for neuron; identifies differentiated neuron Nervous System微管蛋白为球形分子,分为两种类型:a 微管蛋白(a-tubulin) 和B微管蛋白(B -tubulin), 这两种微管蛋白具有相似 的三维结构，能够紧密地结合成二聚体，作为微管组装的亚基，能够聚合并且参与细胞分裂。a和B微管蛋白各有一个GTP结合位点，位于a亚基上的GTP结合位点，是不可逆的结合位点，结合上去的GTP不能被水解，也不能被GDP替换。位于B亚基上的GTP结合位点结合GTP后能够被水解成GDP所以这个位点又称为可交换的位点(exchangeable site,E 位点)-III Tubulin 又名tubulin B -4，是原始神经上皮中所表达的最早的神经元标志物之一。其作为神经元特有标志物，被广泛应用于神经生物学研究。 Noggin: Neuron A neuron-specific gene expressed during the development of n euro ns Neurosphere Embryoid body (E ⑨： ES Cluster of primitive n eural cells in culture of differentiating ES cells; indicates presence of early neurons and glia 星型胶质细胞标志物Astrocyte 、S-100、Microglia Markers Glial fibrillary acidic protein (GFAP) : Astrocyte Protein specifically produced by astrocyte 属于三型中间丝蛋白家族成员，在星型胶质细胞中大量特异性表达。在外周神经系统中的卫星细胞和部分雪旺氏细胞中也有少量表达。神经干细胞也会频繁并大量的表达GFAP因此，GFAP抗体经常被作为星型胶质 细胞的标志物用于神经生物学研究。另外，对于一些来源于星型胶质细胞的脑源性肿瘤，GFAP的表达量也较高。最近研究表明：在位于肝脏的枯否细胞、镜上皮细胞、唾液腺肿瘤细胞和红细胞中亦有GFAP的表达。
一、神经元 （一）神经元的形态结构神经元由胞体和突起两部分组成。胞体包括细胞膜、细胞质和细胞核三部分，突起分树突和轴突(图2-21)。 1.胞体是神经元的营养和代谢中心，形态多样化，有圆形、锥体形、梭形和星形等，胞体主要位于大脑和小脑的皮质、脑干和脊髓的灰质以及神经节内。①细胞膜：为单位膜，具有感受刺激、处理信息、产生和传导神经冲动的功能。②细胞质：除一般细胞器外，还有尼氏体和神经原纤维两种特有的结构。尼氏体（Nissl body）：为强嗜碱性的斑状或颗粒状，轴丘处无尼氏体。神经原纤维（neurofibril ）在HE染色片上不能分辨，在镀银染色片中，神经原纤维被染成棕黑色，呈细丝状，交错排列成网，并伸入到树突和轴突内。 图2-21 神经元的模式图图图2-22 各类神经元的形态结构模式图 它们除了构成神经元的细胞骨架外，还与营养物质、神经递质及离子运输有关。③细胞核：大而圆，位于细胞中央，核仁明显。 2.突起为胞体局部胞膜和胞质向表面伸展形成突起，可分为树突和轴突两种。①树突：每个神经元有一至数个树突，较粗短，形如树枝状，树突内的胞质结构与胞体相似，在其分支上又有许多短小的突起，称树突棘。树突的功能主要是接受刺激。树突和树突棘极大地扩大了神经元的表面积。②轴突：每个神经元只有一个轴突，细而长，长者可达1米以上。胞体
发出轴突的部位常呈圆锥形，称轴丘。轴丘及轴突内无尼氏体。轴突末端分支较多，形成轴突终末。轴突的功能主要是传导神经冲动和释放神经递质。 （二）神经元的分类神经元数量宠大，形态和功能各不相同，一般按其形态及功能分类如下： 1.按神经元突起的数量分类(图2-22) （1）多极神经元从胞体发出一个轴突和多个树突，是人体中最多的一种神经元，如脊髓前角的运动神经元。（2）双极神经元：从胞体两端分别发出一个树突和一个轴突,如视网膜内的双极神经元。（3）假单极神经元：从胞体发生一个突起，但在离胞体不远处即分为两支，一支伸向中枢神经系统，称中枢突(相当于轴突)，另一支伸向周围组织和器官内的感受器，称周围突(相当于树突)。 2. 按神经元的功能分类（1）感觉神经元：又称传入神经元，多为假单极神经元，分布于脑神经节、脊神经节内。（2）中间神经元：又称联络神经元，主要为多极神经元，介于感觉神经元和运动神经元之间。（3）运动神经元：又称传出神经元，多为多极神经元，主要分布于大脑皮质和脊髓前角。
您好！本微课介绍兴奋在神元之间的传递，在完成反射的过程中，兴奋要经过传入、传出等多个神经元，在传入、传出神经上兴奋是以电信号的形式沿神经纤维传导，那么信息是如何从前一个神经元传到后一个神经元的呢？在一个神经元内信号的传导一般为树突接受刺激产生兴奋并传导兴奋至细胞体，神经冲动再从细胞体传至轴突末稍进而传递到下一个神经元。神经元之间是通过什么结构相联系呢？神经元轴突末端经过多次分支最后每个小的分支末端膨大成杯状或球状的小体，叫做突触小体，突触小体可与其他神经元的胞体或树突相接触形成突触，突触的具体结构如何呢？我们来看突触的亚显微结构模式图，突触在结构上包括突触前膜、突触间隙和突触后膜，突触前膜为轴突末端突触小体的膜，突触间隙为突触前膜与突触后膜之间的间隙，突触后膜是与突触前膜相应的另一个神经元的胞体膜或树突膜。由于存在突触间隙兴奋在神经元间就不能以电信号的形式传递，可能怎么传递呢？我们进一步观察突触小体，突触小体内有许多线粒体和突触小泡，突触小泡内有化学物质------神经递质，神经递质可充当信息分子将兴奋从一个神经元传至另一个神经元，具体如何实现传递呢？当神经末稍有神经冲动传来时，突触前膜内的突触小泡受到刺激在线粒体供能的前提下与突触前膜融合进而以胞吐的形式释放神经递质，神经递质扩散通过突触间隙然后与突触后膜上特异性受体结合，引发突触后膜发生电位变化，产生一次新的神经冲动，这样兴奋就从一个神经元通过突触传递给另一个神经元，而在这个过程中实现了电信号到化学信号再到电信号的传递模式的转换。同时，兴奋只能从一个神经元的轴突传递给另一个神经元的胞体或树突，体现单向传递的特点，原因是递质只存在于突触小体内，只能由突触前膜释放，然后作用突触后膜。神经递质传递的都是兴奋性的信号吗？我们进一步了解总结神经递质，神经递质存储的结构为突触小泡，分泌结构为突触前膜，受体位于突触后膜上本质为糖蛋白。神经递质的种类多样，按功能分，可分为兴奋性和抑制性两种，当突触小泡释放兴奋性递质，兴奋性递质与突触后膜上的受体结合，提高膜对离子，特别是对钠离子的通透性引发电位倒转产生兴奋；当突触小泡释放抑制性递质，抑制性递质与突触后膜上的受体结合，提高膜对离子，特别是对氯离子的通透性进一步加大外正内负的膜电位，不易产生兴奋即表现为抑制；所以神经递质的作用是使突触后膜兴奋或抑制。神经递质发挥作用之后去向如何呢？从图中分析可知：递质发挥完效应之后，要么被酶破坏降解或被移走而停止作用，这样可防止突触后膜持续兴奋或者抑制。因此，一次神经冲动只能引起一次递质释放，产生一次突触后电位变化。综上，兴奋在神经元之间的传递过程为：神经冲动刺激突触后小泡使得突触小泡与突触前膜融合，以胞吐的方式释放神经递质，神经递质通过突触间隙后与突触后膜上的特异性受体结合，引发突触后膜电位变化。
β—肌动蛋白的克隆与验证 李亚楠邹曾阳孟冠奇李军张建忠沈彤 摘要：Actin即“肌动蛋白”，是细胞的一种重要骨架蛋白。Actin在不同物种之间高度保守，以至于很难获得较好的针对actin的抗血清。Actin大致可分为六种，其中四种是不同肌肉组织特异性的，包括α-skeletal muscle actin，α-cardiac muscle actin，α-smooth muscle actin，和γ-smooth muscle actin；其余两种广泛分布于各种组织中，包括β-acti n(β-non-muscle)和γ-non-muscle actin。[1]β-Actin是横纹肌肌纤维中的一种主要蛋白质成分，也是肌肉细丝及细胞骨架微丝的主要成分。具有收缩功能，分布广泛。β-Actin是PCR常用的内参，β-Actin抗体是Western Blot 很好的内参指数。内参即是内部参照（Internal Control），对于哺乳动物细胞表达来说一般是指由管家基因编码表达的蛋白。它们在各组织和细胞中的表达相对恒定，在检测蛋白的表达水平变化时常用它来做参照物。[2] 本次实验主要通过PCR的手法来扩增目标蛋白。通过组织细胞提取DNA，用琼脂凝胶电泳来验证是否得到目标DNA；回收后的目标DNA 用PCR仪扩增，并用电泳进行回收；与T载体（PUD-18T）连接；用培养的大肠杆菌DH-5a来制备感受态细胞；将制备完成的感受态细胞均匀的涂布于含有x-gal和IPTG的混合液的LB培养基平板中进行蓝白斑的筛选；最后提取质粒DNA，经验证后保藏菌种。 关键词：β-肌动蛋白横纹肌蛋白质PCR 1材料与方法 1.1 组织细胞DNA提取。[3] 1.1.1 试剂：细胞裂解缓冲液、蛋白酶K、TE缓冲液、酚：氯仿：异戊醇（25:24:1）、7.5mol/l乙酸铵。 器材：胶头滴管、离心机、烧杯、动物组织、研钵、水浴。 1.1.2 方法 取新鲜或冰冻动物组织块0.1g，尽量剪碎，置于石英研钵中，加入1ml的细胞裂解缓冲液匀浆至不见组织块，转入1.5ml离心管中，加入蛋白酶K20微升，混匀。在65℃恒温水浴锅中水浴20min，间歇震荡离心管数次。于台式离心机以
神经元的信息传递的研究 摘要：介绍神经元的结构及功能，阐述神经元的分类以及在人体的信息传递路径，有助于了解神经元类疾病及治疗前景。 关键词：神经元胞体突起病变 简介： 有长突起的细胞，它由细胞体和细胞突起构成。细胞体位于脑、脊髓和神经节中，细胞突起可延伸神经元，又称神经细胞，是构成神经系统结构和功能的基本单位。神经元是具至全身各器官和组织中。细胞体是细胞含核的部分，其形状大小有很大差别，直径约4～120微米。核大而圆，位于细胞中央，染色质少，核仁明显。细胞质内有斑块状的核外染色质（旧称尼尔小体），还有许多神经元纤维。细胞突起是由细胞体延伸出来的细长部分，又可分为树突和轴突。每个神经元可以有一或多个树突，可以接受刺激并将兴奋传入细胞体。每个神经元只有一个轴突，可以把兴奋从胞体传送到另一个神经元或其他组织，如肌肉或腺体。 胞体：神经元的胞体（soma）在于脑和脊髓的灰质及神经节内，其形态各异，常见的形态为星形、锥体形、梨形和圆球形状等。胞体大小不一，直径在5～150μm之间。胞体是神经元的代谢和营养中心。胞体胞体的结构与一般细胞相似，有细胞膜、细胞质（尼氏体及神经原纤维，脂褐素）和细胞核。某些神经元，如下丘脑，具有内分泌功能的分泌神经元（secretory neuron），脑体内含直径I00～30Onm的分泌颗粒，颗粒内含肽类激素（如加压素、催产素等）。 突起：神经元的突起是神经元胞体的延伸部分，由于形态结构和功能的不同，可分为树突和轴突。 树突：是从胞体发出的一至多个突起，呈放射状。胞体起始部分较粗，经反复分支而变细，形如树枝状。树突的结构与脑体相似，胞质内含有尼氏体，线粒体和平行排列的神经原纤维等，但无高尔基复合体。在特殊银染标本上，树突表面可见许多棘状突起，长约0.5～1.0μm，粗约0.5～2.0μm，称树突棘（dendritic spine），是形成突触的部位。一般电镜下，树突棘内含有数个扁平的囊泡称棘器（spine apparatus）。树突的分支和树突棘可扩大神经元接受刺激的表面积。树突具有接受刺激并将冲动传入细胞体的功能。 轴突：每个神经元只有一根胞体发出轴突的细胞质部位多呈贺锥形，称轴丘（axon hillock），其中没有尼氏体，主要有神经原纤维分布。轴突自胞体伸出后，开始的一段，称为起始段（initial segment），长约 15～25μm，通常较树突细，粗细均一，表面光滑，分支较少，无髓鞘包卷。离开胞体一定距离后，有髓鞘包卷，即为有髓神经纤维。轴突末端多呈纤细分支称轴突终未（axon terminal），与其他神经元或效应细胞接触。轴突表面的细胞膜，称轴膜（axolemma）,轴突内的胞质称轴质（axoplasm）或轴浆。轴质内有许多与轴突长袖平行的神经原纤维和细长的线粒体，但无尼氏体和高尔基复合体，因此，轴突内不能合成蛋白质。轴突成分代谢更新以及突触小泡内神经递质，均在胞体内合成，通过轴突内微管、神经丝流向轴突末端。 传递：神经元树突的末端可以接受其他神经传来的信号，并把信号传给神经元，因此是传入神经的末梢。而轴突的分枝可以把神经传给其他神经元或效应器，因此是传出神经的末梢。
Actin(细肌丝)&myosin(粗肌丝)的相对滑动 actin附着到myosin头部(ATPase,— myosin on a prehydrolysis ATP state unbound to actin), 结合后引起myosin头部弯曲, 同时水解ATP→ADP+Pi+能量, 产生一获能的myosin头部(an ADP-Pi-myosin state bound to actin), 发生旋转(pivot), 在依赖Ca2+条件下, 头部结合在相邻的另一个新的actin亚基上↓ 在Pi, ADP相继释放过程中, myosin头部又发生构象变化, 拉动肌动蛋白纤维, 使肌动蛋白纤维细丝与myosin发生相对滑动。 The coupling of ATP hydrolysis to movement of myosin along an actin filament 肌球蛋白与肌动蛋白的相对滑动与ATP水解相偶联的过程。
肌肉收缩—骨骼肌细胞的收缩单位: 肌原纤维(myofibrils)①粗肌丝-肌球蛋白②细肌丝-肌动蛋白(主)+原肌球蛋白+肌钙蛋白 来自脊髓运动神经元的神经冲动 ↓轴突传递 肌肉细胞膜去极化(动作电位产生) ↓T-小管 肌质网: 肌细胞中特化的光面内质网(钙库) 肌质网去极化释放Ca2+至肌浆中 ↓ Ca2+/肌钙蛋白Tn-C结合引起构象变化?actin与Tn I脱离, 变成应力状态; Tn T使原肌球蛋白(Tm)移到actin蛋白螺旋沟深处, 消除actin&myosin结合的障碍(原肌球蛋白Tm位移) ↓ Actin/myosin相对滑动:水解ATP, 化学能转化为机械能; If Ca2+ still 存在继续下一个循环, myosin沿肌动蛋白细丝滑动 ↓ Ca2+回收:神经冲动一经停止, 肌质网主动运输回收Ca2+, 收缩周期停止。
皮层肌动蛋白在肿瘤进展中作用的研究 进展 （作者:___________单位: ___________邮编: ___________） 【摘要】皮层肌动蛋白(cortactin)与多种复杂的细胞进程有关，包括细胞运动性、侵袭性、突触发生、吞噬作用以及肿瘤发生和转移灶的形成。cortactin的过度表达可能以多种途径在侵袭性肿瘤表现型的发展过程起作用，包括增强肌动蛋白聚合作用、下调表皮生长因子受体(epidermal growth factor receptor，EGFR)、调节podosome和invadopodia的形成以及与细胞周期蛋白D1(cyclin D1)和CD44等分子之间相互作用。cortactin作为与癌细胞运动性和侵袭性密切相关的标志物可能成为预测肿瘤患者预后的重要指标。对cortactin的深入研究将为肿瘤的诊断和治疗提供靶向基因。 【关键词】肌动蛋白类·细胞运动·肿瘤转移·肿瘤浸润 Thomas Parson实验室于1993年发现皮层肌动蛋白(cortactin)，它是一种微丝肌动蛋白结合蛋白，还是致癌性酪氨酸激酶v-Src的主要底物[1]。cortactin在细胞骨架重塑过程中发挥重要作用，影响细胞的运动性、侵袭性、突触发生、吞噬以及肿瘤发生和转移灶形成，同时还是连接细胞骨架重建信号通路的关键部分。
1 cortactin分子结构特点及编码基因 cortactin分子结构中包括一个N末端酸性区域，该区域可与Arp2/3复合物结合并使之激活[2]。在cortactin的C末端还包括拥有3个c-Src酪氨酸磷酸化作用位点的富脯氨酸区域和1个SH3结构域，C末端用以调节与多种细胞功能相关的不同蛋白质间的相互作用[1]。cortactin由单一基因(EMS1)编码，但是在SDS聚丙烯酰氨凝胶电泳中却可以显示2个分离的电泳带，分别位于80kDa和85kDa处。它们的差异可能代表两种剪接，也可能因翻译后修饰引起，其中85kDa 亚型的出现可能与肿瘤形成有关[3]。人类cortactin基因CTTN(以前称为EMS1)就位于11q13[4]。在头颈部鳞状细胞癌(HNSCC)内和肝细胞癌中均发现该基因的扩增导致了cortactin的过度表达[4-5]。CTTN扩增和过度表达与HNSCC患者的不良预后直接相关[6]。用11q13扩增不足的细胞进行重组细胞基因过度表达的研究也间接支持这一观点[7]。 2 cortactin的磷酸化 Wu等[1]最初确定cortactin在v-Src转化细胞内的酪氨酸磷酸化作用。Src使cortactin在3个酪氨酸残基(Y421、Y466、Y482)上发生磷酸化[8]。cortactin通过其N末端酸性结构域与Arp2/3复合物结合，并且通过其重复区域与微丝肌动蛋白结合，从而直接激活Arp2/3复合物肌动蛋白核化作用活性[9]。cortactin利用其SH3结构域与发动蛋白2(Dynamin 2)或WIP(WASP-interactin Protein)的结合进一步增强了核化作用活性以及层形足板的突出[10]。
神经元和神经纤维 神经元的分类 神经元的类型很多，按照神经元的功能不同，可以分为三类：①感觉神经元(传入神经元)。它是把神经冲动从外周传到神经中枢的神经元；②运动神经元(传出神经元)。它是把神经冲动从神经中枢传到外周的神经元；③中间神经元(联络神经元)。它是在传入和传出两种神经元之间起联系作用的神经元，位于脑和脊髓内。 此外，还可以按照神经元突起的数目不同，而分为假单极神经元、双极神经元和多极神经元三类(见下图)。假单极神经元由细胞体发出一个突起，在一定距离又分为两支，其中的一支相当于树突，另一支相当于轴突。如脊神经节的神经元是假单极神经元。双极神经元由细胞体发出两个突起，一个是树突，另一个是轴突。如耳蜗神经节的神经元为双极神经元。多极神经元由细胞体发出多个树突和一个轴突。如脊髓等中枢神经系统内的神经元大多属于多极神经元。 神经纤维 神经纤维是由神经元的轴突或长的树突以及套在外面的髓鞘组成的。习惯上把神经纤维分为两类：有髓神经纤维和无髓神经纤维。 有髓神经纤维的轴突外面包有髓鞘。髓鞘呈有规则的节段，两个节段之间的细窄部分叫做郎氏结。周围神经纤维的髓鞘来源于施旺氏细胞，在电镜下观察，可以看到髓鞘是由许多明暗相间的同心圆板层组成的。这种同心圆板层是由施旺氏细胞的细胞膜在轴突周围反复包卷而成的(见下图)。中枢神经纤维的髓鞘来源于少突胶质细胞，由少突胶质细胞的细胞膜包卷轴突而成(其包卷方式与施旺氏细胞包卷方式不同)。
周围神经有髓纤维的髓鞘连续生成的过程示意图 无髓神经纤维过去认为没有髓鞘，现在证明它也有一薄层髓鞘，而不是完全没有髓鞘。在电镜下观察，无髓神经纤维是指一条或多条轴突被包在一个施旺氏细胞内，但细胞膜不作反复的螺旋卷绕，所以不形成具有板层结构的髓鞘(见下图)。由于施旺氏细胞不一定完全包裹这些轴突，所以常有裸露的部分。植物性神经的节后纤维、嗅神经或部分感觉神经纤维属于这类神经纤维。 无髓神经纤维示意图
相关疾病： ?唾液腺肿瘤 ?脑损伤 把最近看过的神经生物学研究中的常用标志物作一总结，与大家分享 每一类列举了常用标志物，有的给出了解释和用途。 神经元轴突标志物 Tau：Neuron Type of MAP; helps maintain structure of the axon ---------------------------------------------------------------------------- 神经元树突标志物Drebrin、MAP、SAP102 微管相关蛋白Microtubule-associated protein-2(MAP-2)：Neuron Dendrite-specific MAP; protein found specifically in dendritic branching of neuron 是组成神经元细胞骨架的重要组成成分，包括：MAP5、MAP1.2和MAP1三种不同类型。在神经系统发育、形成和再生过程的不同时期扮演着重要的角色。其中MAP5为早期微观相关蛋白，在胚胎期和新生动物大脑中有较高表达，并随大脑的逐渐成熟而退化，对神经元突起的生长具有重要的引导作用。MAP2包括三种亚型：MAP2a、MAP2b和MAP2c。其中MAP2b和MAP2c 出现较早。随着年龄的增长MAP2被组织蛋白酶D所降解，在不同类型的神经元中表达量存在差异。 ---------------------------------------------------------------------------------------------- 神经元早期标志物Tubulin、b-4 tubulin ：Neuron Important structural protein for neuron; identifies differentiated neuron Nervous System微管蛋白为球形分子, 分为两种类型:a微管蛋白(a-tubulin)和β微管蛋白(β-tubulin), 这两种微管蛋白具有相似的三维结构, 能够紧密地结合成二聚体, 作为微管组装的亚基，能够聚合并且参与细胞分裂。a和β微管蛋白各有一个GTP结合位点, 位于a亚基上的GTP结合位点, 是不可逆的结合位点，结合上去的GTP不能被水解，也不能被GDP替换。位于β亚基上的GTP结合位点结合GTP后能够被水解成GDP，所以这个位点又称为可交换的位点(exchangeable site,E位点)。β-III Tubulin又名tubulin β-4，是原始神经上皮中所表达的最早的神经元标志物之一。其作为神经元特有标志物，被广泛应用于神经生物学研究。 Noggin：Neuron A neuron-specific gene expressed during the development of neurons Neurosphere Embryoid body (E：ES Cluster of primitive neural cells in culture of differentiating ES cells; indicates presence of early neurons and glia ----------------------------------------------------------------------------------------- 星型胶质细胞标志物Astrocyte、S-100、Microglia Markers Glial fibrillary acidic protein (GFAP) ：Astrocyte Protein specifically produced by astrocyte属于三型中间丝蛋白家族成员，在星型胶质细胞中大量特异性表达。在外周神经系统中的卫星细胞和部分雪旺氏细胞中也有少量表达。神经干细胞也会频繁并大量的表达GFAP。 因此，GFAP抗体经常被作为星型胶质细胞的标志物用于神经生物学研究。另外，对于一些来源于星型胶质细胞的脑源性肿瘤，GFAP 的表达量也较高。最近研究表明：在位于肝脏的枯否细胞、镜上皮细胞、唾液腺肿瘤细胞和红细胞中亦有GFAP的表达。 ------------------------------------------------------------------------------------------- 少突胶质细胞标志物 Myelin basic protein (MP：Oligodendrocyte Protein produced by mature oligodendrocytes; located in the myelin sheath surrounding neuronal structures 髓磷脂Myelin/oligodendrocyte specific protein (MOSP)是由中枢神经系统中少突胶质细胞和外周神经系统中雪旺氏细胞产生特殊蛋白质。是形成髓鞘的主要成分，对于引导神经冲动的传递起着致关重要的作用。多年来，关于髓鞘的形成机理和与其相关的一些先天性疾病的发病机制一直是众多科学家关注的重点。如：多重硬化症和脑白质营养不良等，都与神经系统的去髓鞘化相关。 O4：Oligodendrocyte Cell-surface marker on immature, developing oligodendrocyte O1：Oligodendrocyte Cell-surface marker that characterizes mature oligodendrocyte ----------------------------------------------------------------------------------- 细胞周期抗凋亡蛋白/ 存活素CNPase、OSP、Survivin Survivin：是细胞循环周期中G2/M期表达的一种抗凋亡蛋白。在有丝分裂初期，Survivin与微管之间相互作用，参与调节纺锤体的动态
毕业论文文献综述 生物技术 α-肌动蛋白基因研究现状 摘要：肌动蛋白(actin)是所有真核生物细胞内的重要结构蛋白，有6种亚类，心脏α-actin、骨骼肌α-actin、平滑肌α-actin 是其中的三种，在机体内执行着不同的功能，本文通过阅读大量相关文献综述了它们各自的功缺失、突变后会引起的某些疾病以及一些疾病发生与该种基因表达的影响，所以我们可以通过克隆其基因并进行序列的分析，并研究清楚肌动蛋白基因有利于其他各领域对该基因的应用。 关键字：肌动蛋白；心脏α-actin基因；骨骼肌α-actin基因；平滑肌α-actin基因；研究现状 0前言 肌动蛋白(actin)基因大量存在于几乎所有物种的有核细胞中，是一种高度保守蛋白，与一些管家蛋白的基因一样，在物种内持续恒量表达，因而在很多量化的实验技术如实时定量PCR、Northern 杂交、免疫蛋白印迹中被当作内参照。它是肌肉细胞的一个重要的收缩蛋白，也是细胞骨架的主要组成部分，参与细胞发育进程的多个方面，包括细胞运动、新陈代谢、有丝分裂、肌肉收缩等，在脊椎动物中，actin 家族根据氨基酸序列的不同可分为6 种类型：包括2 种细胞质actin（β 型和γ型），2 种横纹肌型α-actin，即骨骼肌α-actin、心脏α-actin 和2种平滑肌actin，即α-血管平滑肌型、γ-型内脏平滑肌型。近来的研究表明，尽管这些亚型在氨基酸序列上同源性非常高（> 90%），但是不同的actin 基因在功能上是不可互换的[1]。α-肌动蛋白是一种具有2个亚基的蛋白质，其主要作用显然是将肌动蛋白微丝锚定在肌节Z线上，以下是对心脏α-actin基因、骨骼肌α-actin基因、平滑肌α-actin基因这三种分别进行阐述。 1心脏α-actin基因与相关疾病及其研究机理 心脏α-肌动蛋白基因(cardiac alpha-actin, CAA)近年逐渐被认识的在心脏发育过程中起重要作用的一个基因。有研究发现，其突变可导致多种心脏结构及功能异常。心脏α-肌动蛋白(cardiac alpha-actin, CAA)基因是心脏特异表达基因，心脏神经嵴剔除可导致心脏圆锥动脉干发育畸形，有多种基因参与调节，CAA基因就是其中之一[1]。Abdelwahid 等[2]建立CAA基因缺失小鼠模型，其研究发现，胚胎小鼠缺乏心脏α-肌动蛋白基因可导致心肌细胞结构紊乱和过度凋亡，造成发育迟缓和围产期死亡。56%的CAA 基因纯合子缺失小鼠不能存活到出生，剩下的大多在出生后2 周内死亡。 Florian等[3]的研究发现，心脏α-肌动蛋白基因在人类心肌组织表达，但在健康成人主动脉、冠状动脉、脾小梁、结肠、胃及骨骼肌等部位不表达，而在脐带血管、冠状动脉粥样硬化斑块和外周血管粥样硬化斑块等处CAA 基因有表达。由此说明CAA基因可能是一种发育基因，在新生血管组
兴奋在神经元之间的传递 如图是人体缩手反射的反射弧结构简图：方框甲、乙代表神经中枢。当手被尖锐的物体刺痛时，先缩手后产生痛觉。对此生理过程的分析正确的是 A．图中E为感受器，A为效应器，痛觉在图中的甲方框处形成 B．未受刺激时，神经纤维D处的电位分布是膜内为正电位，膜外为负电位 C．图中共5个突触，当手被尖锐的物体刺到发生缩手反射时，反射弧为A→B→C→D→E D．甲代表的低级中枢受乙代表的高级中枢的控制 【参考答案】C 1．如图为反射弧结构示意图，下列与此相关的表述中不正确的是 A．图中包括了感受器、传入神经、神经中枢、传出神经和效应器 B．刺激d时，a处不能测出局部电流 C．在缩手反射中，f仅指手臂肌肉 D．b和c决定了神经冲动只能从e处传到f处 2．如图是反射弧的结构模式图（a、b、c、d、e表示反射弧的组成部分，Ⅰ、Ⅱ表示突触的组成部分），下列有关说法正确的是 A．刺激b的某处产生动作电位时，该处膜便处于外正内负状态 B．若图中的c受损伤，则刺激图中的b仍能实现反射活动 C．当Ⅰ处有神经冲动传来时，会通过主动运输方式将神经递质释放到突触间隙中 D．Ⅱ处的神经递质受体与相应神经递质结合体现了细胞膜的信息传递功能 3．如图表示两个神经元之间的一种连接方式，据图判断下列说法错误的是
A．电信号到达“1”时，依赖“3”结构中的化学物质传递到Ⅱ,但到达Ⅱ时又转换为电信号 B．每个神经元都只有一个轴突，但Ⅰ结构可以有多个，因此一个神经元可以与多个其他神经元的Ⅱ结构构成这种连接 C．同一个神经元的末梢只能释放一种递质，是兴奋性的 D．正常情况下，一次神经冲动只能引起一次递质释放，产生一次突触后膜电位变化 1．【答案】C 【考点】本题考查神经调节的结构基础和方式，意在考查考生运用所学知识，通过比较、分析与综合等方法对相关生物学问题进行解释、推理，做出合理判断或得出正确结论的能力。 2．【答案】D 【解析】刺激b的某处产生动作电位时，Na＋内流，使该处膜处于外负内正状态，A错误；图中的c为感受器，受损伤则不能接受刺激，产生兴奋，刺激图中的b，因为反射弧不完整，所以不叫反射，B错误；当Ⅰ处有神经冲动传来时，会通过胞吐方式将神经递质释放到突触间隙中，C错误；Ⅱ处的神经递质受体与相应神经递质结合体现了细胞膜的信息传递功能，D正确。 3．【答案】C 性的，或者是抑制性的，C错误；正常情况下，一次神经冲动只能引起一次递质释放，产生一次突触后电位变化，D正确。 【点睛】对于B项考生要明确突触的连接方式有多种，主要是轴突—胞体型和轴突—树突型。
神经元活动的一般规律:神经系统神经元,神经纤维突触神经递质.受体学说.神经 营养性作用 神经元是神经系统的结构与功能单位。结构上大致都可分成细胞体和突起两部分，突起又分树突和轴突两种。轴突往往很长，由细胞的轴丘分出，其直径均匀，开始一段称为始段，离开细胞体若干距离后始获得髓鞘，成为神经纤维。习惯上把神经纤维分为有髓纤维与无髓纤维两种，实际上所谓无髓纤维也有一薄层髓鞘，并非完全无髓鞘。 （一）神经纤维传导的特征 神经传导是依靠局部电流来完成的。因此它要求神经纤维在结构和功能上都是完整的；如果神经纤维被切断或局部受麻醉药作用而丧失了完整性，则因局部电流不能很好通过断口或麻醉区而发生传导阻滞。一条神经干中包含着许多条神经纤维，但由于局部电流主要在一条纤维上构成回路，加上各纤维之间存在结缔组织，因此每条纤维传导冲动时基本上互不干扰，表现为传导的绝缘性。人工刺激神经纤维的任何一点引发冲动时，由于局部电流可在刺激点的两端发生，因此冲动可向两端传导，表现为传导的双向性。由于冲动传导耗能极少，比突触传递的耗以小得多，因此神经传导具有相对不疲劳性。 （二）神经纤维传导的速度 一般地说，神经纤维的直径越大，其传导速度也越大；有髓纤维的传导速度与直径成正比，其大致关系为：传导速度（m/s）=6×直径（μm）。一般据说有髓纤维的直径是指包括轴索与髓鞘在一起的总直径，而轴索直径与总直径的比例与传导速度又有密切关系，最适宜的比例为0.6左右。神经纤维的传导速度与温度有关，温度降低则传导速度减慢。 经测定，人的上肢正中神经的运动神经纤维和感觉神经纤维的传导速度分别为58m/s和65m/s。当周围神经发生病变时传导速度减慢。因此测定传导速度有助于诊断神经纤维的疾患和估计神经损伤的预后。 表10-1 神经纤维的分类（一）
第二章第1节课时1 反射及兴奋在神经纤维上 的传导 课下提能 一、选择题 1．下列关于神经元的叙述，正确的是() A．神经元就是神经细胞，一个神经细胞只有一个树突 B．根据神经元传递兴奋的方向，可分为传入神经元、中间神经元和传出神经元 C．神经元能接受刺激产生兴奋，但不能传导兴奋 D．神经元的细胞核位于轴突中 [解析]选B神经元又叫神经细胞，是神经系统结构和功能的基本单位，一个神经元一般有多个树突；能将兴奋从周围部位传向中枢部位的神经元叫传入神经元，将兴奋从中枢部位传向周围部位的神经元叫传出神经元，两者之间的神经元是中间神经元。神经元不仅能接受刺激产生兴奋，还能传导兴奋。神经元的细胞核位于细胞体中。 2．下列关于神经兴奋的叙述，错误的是() A．兴奋在神经纤维上以神经冲动的方式双向传导 B．兴奋部位细胞膜两侧的电位表现为膜内为正、膜外为负 C．神经细胞兴奋时细胞膜对Na＋通透性增大，Na＋外流 D．细胞膜内外K＋、Na＋分布不均匀是神经纤维传导兴奋的基础 [解析]选C神经细胞兴奋时Na＋内流产生动作电位。 3．神经细胞在静息时具有静息电位，受到适宜刺激时可迅速产生能传导的动作电位，这两种电位可通过仪器测量。下面A、B、C、D均为测量神经纤维静息电位示意图(若指针的偏转方向与电流方向相同)，正确的是()
[解析]选C在未受到刺激时，神经纤维处于静息状态，细胞膜两侧的电位表现为内负外正，为静息电位，所以要测量神经纤维的静息电位，电流表的两个电极要分别接在神经纤维的膜外和膜内，且电流必定是从膜外流向膜内。当电流表的两个电极均接在膜外或膜内时，由于两电极间无电位差存在，指针不偏转。 4．如图表示离体神经纤维上的生物电现象，关于此图的分析错误的是() A．甲、丙两处表示未兴奋区域，乙处表示兴奋区域 B．膜外电流的方向为甲→乙，丙→乙 C．乙处产生的兴奋，能刺激甲、丙两处产生兴奋 D．甲处膜外只存在阳离子，乙处膜外只存在阴离子
Xona Microfluidics LLC美国公司神经元突触轴突培养舱Microfluidic Chamber，突触虽然是神经系统重要的功能单位,但针对突触的通用研究方法仍具有一定局限性,有待完善改进,为加深对突触发生、病变现象及机制的研究,MICOFORCE米力光CO本实验设计建立创新性研究方法,实现体外动态观察神经元突触结构的变化。【设计思路】本实验引入新型培养装置Microfluidic Chamber和跨突触结构重组GFP荧光蛋白对mGRASP实现神经元突触体外动态观察。Microfluidic Chamber有双侧培养空间,由微通道相通,仅能允许神经元轴突通过,同时根据流体动力学原理其双侧液体不会发生混合。mGRASP全称为mammalian GFP reconstitution across synaptic partners,包括Pre和Post两个蛋白,分别携带GFP蛋白的一部分,当二者距离约为20 nm左右时,能重组成GFP发出绿色荧光,反之则无荧光信号。Pre和Post通过neurexin和neuroligin固定表达在突触前膜和突触后膜上,利用突触间隙约为20 nm且小于正常细胞间距的原理,用绿色荧光特异性标记突触,体外动态观察突触结构。【实验内容】本实验在新型培养装置Microfluidic Chamber进行孕17天小鼠胎鼠皮层神经元原代培养,体外培养6~7 d,在两侧分别加入携带mGRASP Pre和Post基因的慢病毒感染神经元,基于Microfluidic Chamber良好的液相分隔性,能做到两侧分别表达Pre 和Post蛋白,而不会出现二者同一细胞中共表达的情况。培养4周左右,表达Pre的神经元轴突穿过微通道与另一侧表达Post的神经元接触,形成突触后即可在突触间隙发出绿色荧光。可在培养基中加入神经营养因子或药物,体外动态观察生理、病理刺激对突触结构的影响。【材料】实验动物为孕17 dICR小鼠;Microfluidic Chamber购自Xona Microfluidics公司,货号为RD450;mGRASP基因由Dr. Jinhyun Kim 惠赠。【可行性】在Microfluidic Chamber中进行神经元原代培养为已掌握技术;mGRASP蛋白已在细胞中表达,能检测到绿色荧光,证明实验可行。【创新性】由于突触结构的特性和通用标记方法大多具有细胞毒性,目前尚无较好办法实现神经元突触的体外动态观察,mGRASP作为荧光蛋白无明显细胞毒性,表达后仍可进行长期观察。mGRASP的应用必须基于Pre和Post独立表达,一旦在同一细胞中共表达即可发出绿色荧光,失去特异性标记突触的作用,因此mGRASP多通过定位注射的方式应用于在体实验,本实验设计创新性的利用Microfluidic Chamber良好的液相分隔性,实现了mGRASP的体外应用,进而动态观察突触结构。xona Microfluidics snd150 神经元突触细胞微灌流系统 xona microfluidics snd450 神经元突触细胞微灌流系统 xona microfluidics snd900 神经元突触细胞微灌流系统 xona microfluidics TCND500 神经元突触细胞微灌流系统 xona microfluidics TCND1000 神经元突触细胞微灌流系统 xona microfluidics RD150 神经元突触细胞微灌流系统 xona microfluidics RD450 神经元突触细胞微灌流系统 xona microfluidics RD900 神经元突触细胞微灌流系统 xona microfluidics ULP 神经元突触细胞微灌流系 enlarge image Nat Methods. 2005 Aug;2(8):599-605. A microfluidic culture platform for CNS axonal injury, regeneration and transport. Taylor AM, Blurton-Jones M, Rhee SW, Cribbs DH, Cotman CW, Jeon NL. Investigation of axonal biology in the central nervous
第一节传出神经系统分类 一．神经系统 二.传出神经： 向周围的靶组织传递中枢冲动的神经纤维称为传出神经纤维，由这类神经纤维所构成的神经称为传出神经。 传出神经的基本生理功能 机体多数器官都同时接受去甲肾上腺素能神经与胆碱能神经的双重支配。当去甲肾上腺素能神经兴奋时，表现心脏兴奋，心跳加快，皮肤黏膜与内脏血管收缩，血压上升，支气管和胃肠道平滑肌舒张，瞳孔扩大等，相当于递质去甲肾上腺素的作用。上述生理功能的改变有利于机体机能活动增强和对环境应激反应的需要。 当机体进行休整和能量蓄积时，就发生胆碱能神经节后纤维兴奋过程，基本表现与去甲肾上腺素能神经兴奋时相反的生理效应，即心神经系统 中枢神经 周围神经 传入神经 传出神经
跳弛缓、血管扩张、血压下降、支气管和胃肠平滑肌收缩、瞳孔缩小。 去甲肾上腺素能神经和胆碱能神经对机体多数器官作用基本相反，可是从整体来看，这两类神经功能的相互拮抗并不是对立的，而是在中枢神经系统调节下，它们的功能既对立，又统一,使机体的生理机能更好地适应内、外环境的变化需要，维持正常的生理状态。 三．传出神经系统按解剖学分类 1.植物神经 （1）.植物神经又称自主神经，分为交感神经和副交感神经两类。其都要经过神经节中的突触，更换神经元，然后才达到所支配的器官(平滑肌、心脏、腺体等)。 （2）.植物神经有节前纤维和节后纤维之分 。 (3）.植物神经主要支配心肌、平滑肌和腺体等的活动（不随意的活动）。 传出神经 系 统 植物神经系统 交感神经 副交感神经 （自主神经） 运动神经系统（中途不更换神经元）
2.运动神经： (1).自脊髓发出，直接到达所支配的效应器，中间不更换神 经元。 (2).运动神经自中枢神经系统发出后，中途不更换神经元，直 接到达所支配的骨骼肌。 (3).因此无节前和节后纤维之分。 (4).运动神经支配骨骼肌的运动（随意的活）。 四．传出神经的递质 递质: 当神经冲动传到神经末梢时，从末梢释放传递神经冲动和信号的化学物质。 传出神经末梢释放的递质主要有：乙酰胆碱 (Ach)和去甲肾上腺素 (NA)两种。 五．传出神经按递质分类 1.胆碱能神经 （1）全部交感神经和副交感神经的节前纤维 （2）全部副交感神经的节后纤维 （3）运动神经 （4）少数交感神经的节后纤维