VI_胚層發(fā)育與器官系統(tǒng)發(fā)生I

1、1會(huì)計(jì)學(xué)VI_胚層發(fā)育與器官系統(tǒng)發(fā)生胚層發(fā)育與器官系統(tǒng)發(fā)生I3 The limb development3.1 Formation of the limb bud and limb outgrowth3.2 Generation of the proximal-distal axis of the limb3.3 Specification of the anterior-posterior limb axis 3.4 Generation of the dorsal-ventral axis 3.5 Coordinating the three axes 3.6 Development of

2、 the digits 4 Formation of internal organs, blood vessels, lungs, kindney, heart, and teeth (Option)Development of the vertebrate germ layers and organogenesisDevelopment of the vertebrate germ layers and organogenesis1 Development of the vertebrate germ layers1.1 Ectoderm1.2 Paraxial and intermedia

3、te mesoderm1.3 Lateral plate mesoderm and endoderm2 Development of the nervous system 2.1 The specification of neural cell ( neuron or glial cell) identity2.2 Migration of neurons and the guided outgrowth of axons toward their target cells2.3 Synapse formation and refinementMajor derivatives of the

4、ectoderm germ layerdorsalventralMajor derivatives of the ectoderm germ layerdorsalventralMajor derivatives of the mesoderm germ layerThe major function of the embryonic endoderm is to construct the linings of two tubes within the vertebrate body The digestive tube and its derivatives (liver, gallbla

5、dder, and pancreas)The major function of the embryonic endoderm is to construct the linings of two tubes within the vertebrate body The respiratory tubeThe digestive tube and its derivatives (liver, gallbladder, and pancreas)Development of the germ layers and organogenesis1 Development of the germ l

6、ayers1.1 Ectoderm1.2 Paraxial and intermediate mesoderm1.3 Lateral plate mesoderm and endoderm2 Development of the nervous system 2.1 The specification of neural cell ( neuron or glial cell) identity2.2 Migration of neurons and the guided outgrowth of axons toward their target cells2.3 Synapse forma

7、tion and refinementDevelopment of the nervous systemn The nervous system is the most complex of all the organ systems in the animal embryo. In mammals, for example, billions of nerve cells, or neurons, develop a highly organized pattern of connections, creating the neuronal network that makes up the

8、 functioning brain and the rest of the nervous system.n The nervous system contains many hundreds of different types of neurons, varying in sizes, shapes and functions. The nervous system can only function properly if the neurons are correctly connected to one another, thus a central question in ner

9、vous system development is how the connections between neurons with each other and with other target cells develop with the appropriate specificity.Development of the nervous systemn Neurons connect with each other and with other target cells, such as muscle, at specilized junctions known as synapse

10、s（突觸突觸）. n A neuron receives input from other neurons through its highly branched dendrites, and generate a nerve impulse at the cell body. This nerve impulse is then conducted along the axon to the axon terminal, which makes a synapse with the dendrites or cell body of another neuron or with the su

11、rface of a muscle cell.n The dendrites and axon terminals of individual neurons can be extensively branched, and a single neuron in the CNS can receive as many as 100,000 different input.Development of the nervous systemn Development of the nervous system involve neuronal cell differentiation, morph

12、ogenesis, and migrationn The overall process of nervous-system development can be divided up into four major stages:The specification of neural cell (neuron or glial cell) identityThe migration of neurons and the outgrowth of axons to their targetsThe formation of synapses between neurons with each

13、other and with other tragets, such as muscle etcThe refinement of synaptic connections through the elimination of axon branches and cell deathDevelopment of the germ layers and organogenesis1 Development of the germ layers1.1 Ectoderm1.2 Paraxial and intermediate mesoderm1.3 Lateral plate mesoderm a

14、nd endoderm2 Development of the nervous system 2.1 The specification of neural cell ( neuron or glial cell) identity2.2 Migration of neurons and the guided outgrowth of axons toward their target cells2.3 Synapse formation and refinementDevelopment of the germ layers and organogenesis1 Development of

15、 the germ layers1.1 Ectoderm1.2 Paraxial and intermediate mesoderm1.3 Lateral plate mesoderm and endoderm2 Development of the nervous system 2.1 The specification of neural cell ( neuron or glial cell) identity2.2 Migration of neurons and the guided outgrowth of axons toward their target cells2.3 Sy

16、napse formation and refinementThe presumptive nervous system is specified early in embryonic development in both invertebrates and vertebratesThe presumptive nervous system is specified early in embryonic development in both invertebrates and vertebratesSpecification of the neuronal precursors invol

17、ves lateral inhibition in both invertebrates and vertebratesn In Drosophila, the neurectoderm is subdivided along the AP and DV axes into a precise orthogonal （直角直角） pattern of proneural clusters. Within each cluster, cell-cell interactions through lateral inhibition direct one cell into a neural pr

18、ecursor or neuroblast fate. The rest become epidermal cells.n As in Drosophila, lateral inhibition specifies single cells as neuronal precursors in the vertebrate nervous system.Further development of neurons from neuronal precursors involves asymmetric cell division in DrosophilaAfter specification

19、, the Drosophila neuroblasts delaminate from the neurectodermal epithelium to lie adjacent to its inner, or basal face, and then behave as a stem cells. Each neuroblast divides asymmetrically to give an apical cell, which remains a neural stem cell, and a smaller basal cell, the ganglion mother cell

20、 (GMCs), which will differentiate into neurons.The localized protein determinants in neuroblasts specify the orientation of cell division and daughter cell fate:Numb: the ganglion mother cell fateInsc/Pins: the orientation of the plane of cell divisionBazooka Prospero/Miranda Numb The pattern of dif

21、ferentiation of cells along the DV axis of the spinal cord depends on ventral and dorsal signalsn There is a distinct dorso-ventral pattern in the developing spinal cord. Specifically, different types of neurons differentiate along the DV axis. Motor neurons and interneurons are located ventrally, w

22、hereas commissural neurons （連合神經(jīng)元連合神經(jīng)元）differentiate in the dorsal regionn Differentiation of neuronal subtypes along the DV axis is determined by Sonic hedgehog protein (Shh), the ventral signal secreted by the notochord, and BMPs, the dorsal signal from the dorsal epidermal ectodermBMP signalShh s

23、ignalThe neurons of the spinal cord are given their identity by exposure to the gradients of two signal proteinsThe graded signal proteins cause different transcriptional factors to be activated in the nuclei of the neuronal cells, depending on their position along the DV axisA graded Sonic hedgehog

24、 signal patterns different neuronal types in the ventral region of the spinal cord through regulating two classes of homeodomain protein genesThe distribution pattern of the signal proteins and homeodomain proteins in chick neural tube along the DV axisBMPsShhPax7Pax6Nkx6.1F: Chick neural tubeG: In

25、situ hybridization for 3 Homeodomain proteins. Where Nkx6.1 and Pax6 overlap, the motor neurons become specified.MNsMNsDevelopment of the germ layers and organogenesis1 Development of the germ layers1.1 Ectoderm1.2 Paraxial and intermediate mesoderm1.3 Lateral plate mesoderm and endoderm2 Developmen

26、t of the nervous system 2.1 The specification of neural cell ( neuron or glial cell) identity2.2 Migration of neurons and the guided outgrowth of axons toward their target cells2.3 Synapse formation and refinementThe developmental process for establishing the functioning network of neuronsn Migratio

27、n of immature neuronsThe migration of neural crest cellsWhat controls the the neural crest migration?n Outgrowth of axons toward their targetsHow is the growth of axons guided?What are the mechanisms underlying the axon guidance? The functioning neuronal network involves both migration of immature n

28、eurons and outgrowth of axons toward their targets (I)n Neural crest cells and axonal outgrowth of neurons share the property of having to migrate far from their source of origin to specific places in the embryoThey both need to recognize cues (信號(hào)信號(hào)) to begin this migration, and respond to signals t

29、hat guide them along specific routes to their final destinationMany of the signals recognized by neural crest cells and by axonal growth cones are the same The functioning neuronal network involves both migration of immature neurons and outgrowth of axons toward their targets (II) The functioning ne

30、uronal network involves both migration of immature neurons and outgrowth of axons toward their targets (I)n Migration of immature neuronsThe migration of neural crest cellsWhat controls the the neural crest migration?n Outgrowth of axons toward their targetsHow is the growth of axons guided?What are

31、 the mechanisms underlying the axon guidance? dorsalventralThe neural crest cells migrate extensively to generate a large number of differentiated cell types The fate of the neural crest cells depends, to a large degree, on where they migrate to and settleThe neural crest can be divided into 4 main

32、domains (overlapping), each with characteristic derivatives and functionsl The cranial (cephalic 頭部頭部) neural crest cells： The cartilage, bone, cranial neurons, glia and connective tissues of the facel The trunk neural crest cells The dorsal root ganglia containing the sensory neurons The sympatheti

33、c ganglia, the adrenal medulla, melanocytes etcl The vagal (neck) and sacral (骶骶) neural crest cells Parasympathetic ganglia of the gutl The cardiac neural crest cells Melanocytes, neurons, cartilage, and connective tissues The entire muscular-connective tissue wall of the large arteriesNeural crest

34、 cell migration is controlled by environmental cues and adhensive differences (I)n The adhensive differences The dynamic expression of N-cadherin in neural crest cells is essential for the initiation of neural crest cells, the segragation of the neural crest cells from the neural tube. ( N-cadherin

35、is expressed in neural crest cells prior to migration, and after migration. But, down-regulation of N-cadherin expression at the time of migration, and turning off of N-cadherin expression during migration)Constitutive expression of N-cadherin dramatically supresses the movement of the neural crest

36、cells from the neural tube.Neural crest cell migration is controlled by environmental cues and adhensive differences (II)n The environmental cues (cues from the extracellular matrices) Migration-promoting proteins : fibronectin (纖維連接蛋白纖維連接蛋白), laminin (層粘連蛋白層粘連蛋白), various collagen molecules, and pr

37、oteoglycans etc ( by binding to integrin in neural crest cells) Migration-impeding proteins : the ephrin proteins (by binding to Eph receptor in neural crest cell membranes)Ephrin functions as a repulsive signal for neural crest cell migrationA: Negative correlation between regions of the ephrin in

38、the sclerotome生骨節(jié) and the presence of neural crest cellsB: When neural crest cells are plated on fibronectin-containing matrices with alternating stripes of ephrin, they bind to thoe regions lacking ephrinC: Composite scheme showing the migration of spinal cord neural crest cells and motor neurons t

39、hrough the ephrin-deficient anterior regions of the sclerotomes The functioning neuronal network involves both migration of immature neurons and outgrowth of axons toward their targets (I)n Migration of immature neuronsThe migration of neural crest cellsWhat controls the the neural crest migration?n

40、 Outgrowth of axons toward their targetsHow is the growth of axons guided?What are the mechanisms underlying the axon guidance? The growth cone controls the path taken by the growing axon Dendrites are the fine, branching extensions of the neuron that are used to pick up electric impulses from other

41、 cells. In human, the average cortical neuron connects with 10,000 other neural cells. Axon is a continuous extension of the nerve cell body which may be several feet long. Neurons make functional connections with their targets through outgrowth of axons. The outgrowth of the axon is guided by the g

42、rowth cone at the axon tip The growth cone moves by the elongation and contraction of pointed filopodia called microspikes (微突微突). These microspikes contain actin microfilaments, which are oriented parallel to the long axis of the axon.The growth cone controls the path taken by the growing axonactin

43、tubulinThe growth cone both moves and senses its environment, functioning as both locomotor and sensory apparatusn In general, the growth cone moves in the direction in which its filopodia make the most stable contacts with other cells and with the extracellular matrix. n The extracellular signals c

44、an bind to receptors on the growth cone surface, and influence its direction of migration. The extension and retraction of filopodia involves the assembly and disassembly of the actin cytoskeleton. Members of a family of intracellular signaling proteins, the Ras-related GTPases, are involved in the

45、reorganization of the actin cytoskeleton: Activation of Rho cause growth cones to stop extendingRac and Cdc42 are involved in growth-cone extensionn How growth cones transduce extracellular signals so as to extend or collapse filopodia is not fully understood.The growth cone controls the path taken

46、by the growing axonAxon growth cones are guided by two main types of cueattractive and repulsive signals n Chemoattractant proteins Netrins Cadherinsn Chemorepellants proteinsSemaphorinsEphrinSlit proteinsn These signal proteins often function as both attractants and repellants, depending on the cel

47、lular contextAxon growth cones are guided by two main types of cue-attractive and repulsiveNetrin-1 is a key attractant produced in the floor plate and in the middlelineMotor neurons from the spinal cord make muscle specific connections controlled by EphA signalingDevelopment of the germ layers and

48、organogenesis1 Development of the germ layers1.1 Ectoderm1.2 Paraxial and intermediate mesoderm1.3 Lateral plate mesoderm and endoderm2 Development of the nervous system 2.1 The specification of neural cell ( neuron or glial cell) identity2.2 Migration of neurons and the guided outgrowth of axons to

49、ward their target cells2.3 Synapse formation and refinementSynapse formation and refinement (I)n When axons reach their targets they form specialized junctions called synapses. Neurotransmitters from the axon terminal are released at these synapses to depolarize or hyperpolarize of the membrane of t

50、he target cell across the synaptic cleftn Neurons can make connections with other nerve cells, with muscles, and also with certain glandular tissues. The vertebrate neuromuscular junction (NMJ) between motor neuron and muscle cell is a best studied synapse, studies of which significantly contribute

51、to the understanding of synapse formationn Synapse formation involves reciprocal signaling interactions between neuron and muscle cell (NMJ) or axons and dendrites of neurons (Interneuronal synapse).Synapse formation within the neurons in the CNS follows similar principles with the NMJSynapse format

52、ion and refinement (II)n The functioning of the nervous system depends on the establishment of the specific synapses between neurons and their targets. It means that initial synaptic connections need to be refined. n This is well studied in synapse formation of the NMJ. Specificity of synapses appea

53、rs to be achieved by an initial overproduction of neurons that compete for targets, with many neurons dying during development. Further, refinement of synaptic connections involves competition between synapses. n Initially, most mammalian muscle fibers are innervated（支配）（支配）by two or more motor neur

54、ons. With time, due to the competition, most of the synaptic connections are eliminated so that a single fiber is eventually innervated by only one motor neuron Major derivatives of the ectoderm germ layerdorsalventralDevelopment of the germ layers and organogenesis1 Development of the germ layers1.1 Ectoderm1.2 Paraxial and intermediate mesoderm1.3 Lateral plate mesoderm and endoderm2 Development of the nervous system 2.1 The specification of neural cell ( neuron or glial cell) identity2.2 Migration of neurons and the guided outg