神经发生课件

1、脑发育与神经细胞发生张家兴Email: Part I 脑发育 Brain Development一、外胚层（ectoderm） 神经管（neural tube）在受精后第18天，胚胎植入子宫壁，这时胚胎由外胚层、中胚层和内胚层组成。外胚层增厚形成神经盘(b) 在第 20 天神经槽形成(c) 在第 22 天神经槽闭合形成神经管 (d) 在第 24 天形成：端脑（ telencephalon）、 间脑（diencephalon）、中脑（mesencephalon）、 菱脑（rhombencephalon）The neural plate is induced by signals from adj

2、acent mesodermThe neural plate is patterned along its dorso-ventral axis by signals from adjacent non-neural cells The ventral NT the notochord The dorsal NT the epidermal ectoderm neural plateneural grooveneural foldneural tubeneural tube神经管形成的扫描电镜图 前脑泡 头端：向两侧膨大，形成左右两个端脑 尾端：形成间脑中脑泡 中脑菱脑泡 头段：形成后脑，演化

3、为脑桥和小脑 末段：形成末脑，演化为延髓 第6周 端脑 间脑 中脑 后脑 末脑 神经管管腔的演变：前脑泡腔 两侧的侧脑室和间脑的第3脑室中脑泡腔 中脑导水管菱脑泡腔 第4脑室侧脑室第3脑室导水管第4脑室三、脑发育畸形（brain malformation）脑小畸形无脑畸形无脑回畸形脑穿通畸形巨脑回畸形Part II 胚胎和胎儿阶段脑内神经发生Neural Development in Embryo and Fetus增殖（Proliferation）迁移（Migration）分化（Differentiation）聚集（Aggregation）突触形成（Synaptogenesis）神经元死亡（

4、Neuron Death）突触重排（Synapse Rearrangement）髓鞘化（Myelination）神经发生的八个阶段2. 迁移（Migration） 当细胞在室管带增殖后，迁移就开始了； 迁移的细胞是不成熟的，没有轴突和树突之分； 迁移的同时出现细胞分化。A:神经细胞迁移过程中,有领先突起。领先突起有分枝,动态竞争,其中一枝成为主干,带领细胞体的移动,其后,又不断重复分枝竞争,决定细胞移动方向。B:迁移的神经细胞也可以原来领先突起的生长锥消失,在细胞体完全相反的一边长出新的突起,导致细胞180度转向。迁移的神经细胞鼠脑室管膜下带细胞：肌动蛋白丝染绿色微管红色AB迁移的两种方法：

5、(1)胞体迁移（Somal migration） (2)胶质细胞介导的迁移（Glial-mediated migration）Migration-放射胶质细胞（Radial Glia）Radial glial cells act as guide wires for the migration of neuronsRadial Glial Cells: Are They Really Glia?PS: 软膜表面; MZ: 边缘带; CP: 皮质板; SP: 底板; IZ: 中间带; SVZ: 亚室管膜层; VZ: 室管膜层; RG: 辐射状神经胶质细胞细胞迁移与大脑皮层的形成（inside-o

6、utside）以小鼠为例。 皮层发育时先形成内层, 后形成靠近边缘的外层皮层神经细胞迁移模式3. 分化（Differentiation）Cortical progenitor cells follow an intrinsic developmental sequence both in vivo and in vitro. A, astrocyte; N, neuron; O, oligodendrocyte; P, progenitor cell 神经元命运的确定lateral inhibition跨膜蛋白Delta和Notch的相互作用在神经元命运确定中起关键作用。二者相互作用后，Not

7、ch通过一系列反应抑制Neuro D和Neurogenin的表达。Neurogenin是激活Delta表达所必需的。诱导细胞分化的因素5. 突触形成（Synaptogenesis）1 neuron makes up to 1000 synapses with other neuronsSynapse FormationSynapse junction between axon and another neuron (where neurotransmission takes place) composed of presynaptic terminal, synaptic gap and po

8、stsynaptic site(Prokop et al., 1996)Yoshimura, T. et al. J. Neurosci. 2006;26:10626-10630伪足形成（Lamellipodia）短小突起形成轴突（ axon）形成树突（ dendrites）形成突触形成神经突起 (Neurite)生长锥（Growth Cones）Growth cones crawl forward as they elaborate the axons training behind them. Their extension is controlled by cues in their o

9、utside environment that ultimately direct them toward their appropriate targets生长锥的形成是由骨架网格所含运动蛋白actin 和 肌球蛋白（myosin）介导Major elements of the cytoskeleton： microtubules tubulin polymers provide structure support and act as conveyers microfilaments actin polymers predominantly in growth cone neurofila

10、ments support radial growthMAPs (MAP2, tau) promote assembly and stabilize microtubules(Sanes, Reh, and Harris, 2006)Cytoskeletal components of axons and dendrites differDuring development in primary neuronal cultures: Tau gradually segregates into axons MAP2 segregates into dendrites a combination

11、of protein stability, differential protein sorting, and dendrite-specific transport of MAP2 mRNA are responsible for spatial segregationcourtesy of P. Lein调节突起生长的外界因子ECM-associatedlamininfibronectinheparin sulfatesCAMsN-cadherinNCAML1Neurotrophic factors NGFBDNFGDNFNT-3,4BMPInhibitoryCSPGsNG2MAGNogo

12、GuidingsemaphorinsephrinsnetrinsslitsPermissive(Yoshimura, T. et al. J. Neurosci. 2006;26:10626-10630)细胞外基质 (ECMs)调节突起生长的细胞内分子机制Factors regulating synapse formation(Goda and Davis, 2003)during neurite outgrowth genes encoding pre and postsynaptic proteins expressed, priming factors released by neuro

13、ns and glia (e.g. FGF, Wnts, NTs, cholesterol)cell adhesion molecules (e.g. N-CAM, SynCAM) stabilize contact sitesdifferentiation into pre and postsynaptic elements promoted by signaling of neurolignin and Wnt-7 via neurixin and frizzled. Active zone elements (vesicles, receptors) accumulate.synapti

14、c vesicles docked and receptors embedded in PSD scaffold.Synaptogenesis the formation of synapses The number of synapses reaches a maximum at about 2 years of age;After this, pruning begins;By 16, only half of the original synapses remain.(Sanes, Reh, and Harris, 2006)(Fletcher et al., J. Neurosci.,

15、 1994)synapse formation in primary hippocampal cellssynapse formation in cat visual cortexSynapse Formation Characterization and AssessmentMicroscopic assessment of synapses(Use of pre and postsynaptic proteins as markers)(Abcam 2007)SYNAPSINpresynaptic vesicle proteinpostsynaptic density protein, P

16、SDGenesis of connection: for exampleThe three phases of pathway formation Pathway selection pathTarget selection structureAddress selection cellThe three phases depends on :Direct cell-to-cell contractContract between cells and extracellular secretions of other cellCommunication via action potential

17、s and synaptic transmission About 100 billion neurons in brain - remarkably precise interconnection among them - to perform the functions of the brain.Axons locate their target tissues by using chemical attractants (blue) and repellants (orange) located around or on the surface of guide cells. Left:

18、 An axon begins to grow toward target tissue. Guide cells 1 and 3 secrete attractants that cause the axon to grow toward them, while guide cell 2 secretes a repellant. Surfaces of guide cells and target tissues also display attractant molecules (blue) and repellant molecules (orange). Right: A day l

19、ater, the axon has grown around only guide cells 1 and 3. Sperrys experimentSperry took advantage of the fact that in amphibians, the optic nerve will regrow after it has been interrupted Sperry cut the optic nerve and simultaneously rotated the eye 180 degrees in the eye socket.In learning movement

20、s to catch prey, the part of the retina now looking forward (backward) should connect to the part of the brain which causes forward (backward) movement.The conclusion from this is that the pattern of connections between retina and tectum, and the movement information represented is not based on expe

21、rience.It is innate based on the initial distribution of chemical markers in the brain.一个出生不久男婴的一只眼睛因为感染被绷带缠了两个星期，而导致该眼睛失明。原因在于，在婴儿视神经与脑皮层的目标区域建立联系的关键时刻，被绷带缠住的那个眼的神经元不能发出正常工作信号，因此它们的目标区域被其它神经元所占据。The role of the environment6. 死亡（Death）Summary of possible cell death mechanisms for cells in the prolif

22、erative zoneAbout 40-75% of all neurons born in embryonic and fetal development do not survive during migration and differentiationNeuron Death Leads to Synapse RearrangementRelease and uptake of neurotrophic factorsNeurons receiving insufficient neurotropic factor dieAxonal processes complete for l

23、imited neurotrophic factor7. 突触重排（Synapse Rearrangement）Active synapses likely take up neurotrophic factor that maintains the synapseInactive synapses get too little trophic factor to remain stableThe two input neurons in one eye (top) fire at the same time, this is sufficient to cause the top LGN t

24、arget neuron to fire but not the bottom one. This is the same situation as in part a, except that now the two input neurons in the other eye (bottom) are active simultaneously, causing the bottom target neuron to fire.Over time, neurons that fire together wire together. Notice also that input cells

25、that fire out of sync with the target lose their link.LGNSegregation of ocular dominance columns in cat striate contexInitially the inputs from the LGN serving the eyes (different colour) are intermingled in layer IV. Over the course of fetal and early postnatal development, the inputs from the eyes

26、 segregate into ocular dominance columns in layer IV.Changes in synaptic capacity神经元胞体、树突和别的神经元之间形成一定数目突触的能力叫“ synaptic capacity”突触数目形成能力最高阶段在发育早期，随后逐渐减少。在恒河猴的视觉皮层减少约50%，减少速度5000个/秒。8. 髓鞘化（Myelination）Myelination lasts for up to 30 YearsBrain Weight During Development and AgingCritical PeriodsPart I

27、I 成年脑内神经发生Neurogenesis in Adult BrainThe rise and fall of thecentral dogma of neurobiologyThe belief that, in the adult life, neurons can only die and no new neurons are generated can be regarded as the central dogma of neurobiology, which has strongly influenced basic and applied neuroscience resea

28、rch as well as clinical practice.The adult nervous system was considered a perennial tissueThe establishment of the dogma1. Clinical2. Related to neural functions3. Related to the theory of learning and memory4. Technical and experimental (1) Specific diffusible glycoproteins：NGF、bFGF or FGF2、PDGF (

29、2) Specific cellular markers: NSE, GFAP (3) 5-bromo-2-deoxyuridine (BrdU) (4) New techniques: fluorescent and confocal microscopy (5) Gene transferBioessays. 2008 Feb;30(2):135-45.Colucci-DAmato L, di Porzio U. Bioessays. 2008 Feb;30(2):135-45 SongbirdsHVCHigher Vocal Center Doubles in Size in the S

30、pringWhat causes this increase in size?New neurons are born!What mediates the neurogenesis?TestosteroneTestosterone levels increase with environmental cues of springTestosterone leads to increases in neurotrophic factors and more survival of new neurons一、History of adult neurogenesisLandmarks in neu

31、rogenesis and NSC discoveriesColucci-DAmato L, di Porzio U. Bioessays. 2008;30(2):135-45 Paton JA, Nottebohm FN. Neurons generated in the adult brain are recruited into functional circuits. Science 1984;225:10461048.Eriksson PS, Perfilieva E, Bjork-Eriksson T, Alborn AM, Nordborg C, et al. Neurogenesis in the adult human hippocampus. Nat Med 1998;4:13131317.二、Neurogenesis in the Adu