Developmental Biology 第三章神经系统的发育
Developmental Biology 第三章 神经系统的发育
Developmental Biology 神经管的形成 称为 neurulation。其方式分 primary neurulati0n的 神经管( neural tube是中枢神经系统的原基,其 secondary neurulation两种。 Primary neurulation: 由外胚层细胞增殖、内陷并最终离开外胚层表面而形 成中空的神经管。绝大多数脊椎动物前部神经管的形成采 用此种方式
Developmental Biology 一、神经管的形成 神经管(neural tube)是中枢神经系统的原基，其形成 称为neurulation。其方式分primary neurulation和 secondary neurulation两种。 1. Primary neurulation: 由外胚层细胞增殖、内陷并最终离开外胚层表面而形 成中空的神经管。绝大多数脊椎动物前部神经管的形成采 用此种方式
Developmental Biology 外胚层细胞的命运:背部中线区的细胞将形成脑和脊髓;中线区 外侧的细胞将生成皮肤;上述二者相交处的细胞为神经嵴细胞 neural crest),它们将迁移各处形成外周神经元、色素细胞、神经胶质细胞等。 Neural plate Neural fold /⑦ Neural cnst igure 7.2 Neurulation in amphibians and amniotes. (A) Diagrammatic representation of neural tube formation. The ectodermal cells are represented either as precursors of the neural crest(black)or as precursors of the epidermis(color). The ectoderm folds in at the most dorsal point, forming an outer epidermis and an inner neural tube connected by neural crest cells. B)Photomicrographs of neurulation in a 2-ay chick embryo. (C)Neural tube formation seen in transverse cross sections of the chick embryo at the region of the future midbrain (arrowheads in B). Each photo- raph in(C) corresponds to the one above it.(HE, head fold: HP, head process; IIN Epid Henscn's node: M, midbrain; NP, neural plate. )(Photomicrographs courtesy of R. Nagele
Developmental Biology 外胚层细胞的命运：背部中线区的细胞将形成脑和脊髓；中线区 外侧的细胞将生成皮肤；上述二者相交处的细胞为神经嵴细胞(neural crest)，它们将迁移各处形成外周神经元、色素细胞、神经胶质细胞等
Developmental Biology 神经管形成的起始:来自背部中胚层的信号诱导预 置神经板边缘的细胞的背测收缩,而预置的表皮细胞向 中线移动,使表皮与神经板交接处凸起形成神经褶。 mh MtMMliDy apical constriction cell movement Fig 8.29 Change in cell shape and cell crawling may drive ectoderm. This may be partly responsible for causing the neural neural folding. Cells at the edge of the neural plate change their folds to develop shape and appear to crawl along the undersurface of the adjacent
Developmental Biology 神经管形成的起始：来自背部中胚层的信号诱导预 置神经板边缘的细胞的背测收缩，而预置的表皮细胞向 中线移动，使表皮与神经板交接处凸起形成神经褶
Developmental Biology Primary neurulation的过程 (A)Formation of neural folds (B)Elevation of neural folds Presumptive 沙 Notochord DLHP DLHP Presumptive neural plate r Furrowing Transition zone MHP Wedging Neural plate Epidermis Anchoring Notochord Figure 7.4 anchored to the notochord the neural Schematic representation of the epithe- folds are elevated. These movements lial bending during chick neurulation. appear to be continued as the medially (A)Formation of neural folds occurs moving epidermis drags the neural when presumptive epidermal cells plate with it, resulting in the apposition move medially toward the center of the of the neural folds. (C)In the three embryo. This presumptive epidermis hinge regions(the medial hinge point, pushes the neural plate under it as it MHP and the two dorsolateral hing moves.(B)As the midline cells of the neural plate( the floor plate cells)are positions, the DLHP), the neural plate lls change their length and constrict at their apice
Developmental Biology Primary neurulation的过程
DevelopmerAIEa 神经管形成的 越 扫描电镜图 Figure 7. 8 graph of neural tube formation in the chick embryo. (A) Neural groove surrounded by mesenchymal cells(B)Elongated neural epithelial cells form a tube as the fattened epidermal cells ate brought to the midline of th embryo. The MIP cells form a hinge at the bottom of the tube, while the neural plate cells attache to the basal area of the surtace ectoderm form the dorsolateral inge regions. These three hinges can be seen as furrows.(C) Neural tube torma tion is complete. The cells that had been the neural plate are now inside the embryo. Ihe presumptive epidermis lies atop the tube, nd the neural tube is flanked on its sides by the mesoderm al somites and on the bottom by the noto chord (Photographs courtesy of K w. looney
Developmental Biology 神经管形成的 扫描电镜图
Developmental Biology 神经管与相邻外胚层细胞分离可能与细胞粘连分子有关 Cadherin expression during neural tube formation in a Xenopus embryo E cadherin N-cadherin N-CAM 八0⑥ cloderm neural plate Misexpression ol N-cadherin Fig 8. 31 Expression of cell adhesion molecules during neural tube formation in Xenopus. The cells of the neural plate express N-cadhenn and the adjacent ectoderm expresses E-cadherin. If N-cadherin is misexpressed in the ectoderm on one side, there is a failure of the neural tube to separate at that site (nght
Developmental Biology 神经管与相邻外胚层细胞分离可能与细胞粘连分子有关
Developmental Biol neural told Fig 2.17 Development of the neural ube and mesoderm in the chick mbryo. Once the notochord has rmed, neurulation begins, following notochord formation in an anterior to neural posterior direction. The figure shows a foregut series of sections along the antero notochord posterior axis of a chick embryo Neural tube formation is well advanced at the extra-embryonic nterior end(top two sections), where mesoderm the head fold has already separated the head fold future head from the rest of the blastoderm and the ventral body fold has brought neural plate endoderm from both sides of the body gether to form the gut. During neurulation, 神经管沿Am the neural plate changes shape: neural folds rise up on either side and form a P轴线依次闭 tube when they meet in the midline. The will give rise to head structures. Further 合,完成形成 neural fold back(middle section). in the future trunk egion of the embryo, notochord and 过程。 neural groove starting. At the posterior end, behind Hensen s node( bottom section), notochord termediate formation somite formation and neuru- exoderm lation have not yet begun. The mesoderm coelom internalized through the primitive streak somatic starts to form structures appropriate to its sition along the antero-posterior and dorso-ventral axes. For example, in the mesoderm future trunk region, the intermediate mesoderm will form the mesodermal arts of the kidney and the splanchnic mesoderm will give rise to the heart neural folds The body fold will continue down the and also bringing paired organ rudiments Hensen's node that initially form on each side of the midline(e.g. those of the heart and dorsal aorta) together to form the final organs lying ventral to the gut. Blood biood island slands, from which the first blood cel primitive groove are produced, form from the ventral- primitive ridge After Patten, B.M. 1971
Developmental Biology 神经管沿A －P 轴线依次闭 合，完成形成 过程
Developmental Biology 人类胚胎的神经管闭合缺陷症 不同区域的神经管的封口时间不同。第二区封口失败,胚胎的前脑不发育,即 致死性的无脑症;第5区不封口导致脊柱裂口症 Sonic hedgehog、Pax3等因子是神经管闭合所必需的。孕妇服用叶酸和适量的 胆固醇可降低胎儿神经管缺陷的风险 Neural fold Anterior Pericardial neuropore bulg Otic placode Pericardia bulge 4 somites ? edg of amnion Posterior neuropore 22 Days 23 Days Normal Spina bifida Figure 7.10 Neurulation in human embryos. (A)Dorsal and transverse sections of a 22-day human embryo initiating neurulation. Both anterior and posterior neuropores are open to the amniotic fluid. (B) Dorsal view of a neurulating human embryo a day later. The anterior neuropore region is closing while the posterior neuropore remains open.(C) Regions of neural tube closure postulated by genetic evidence (superimposed on newborn body). D) Anencephaly due to failure of neural plate fusion in region 2(E) Spina bifida due to failure of region 5 to fuse (or for the pos teriormost neuropore to close). (C-E after Van Allen et al., 1993
Developmental Biology 人类胚胎的神经管闭合缺陷症 不同区域的神经管的封口时间不同。第二区封口失败，胚胎的前脑不发育，即 致死性的无脑症；第5区不封口导致脊柱裂口症。 Sonic Hedgehog、Pax3等因子是神经管闭合所必需的。孕妇服用叶酸和适量的 胆固醇可降低胎儿神经管缺陷的风险
Developmental Biology 2. Secondary Neurulation Figure 7.13 mation of dary neural tube in the 25-s medullary cord forming at the most caudal end of the chick tailbud. B) Medullary slightly more anterior in the tailbud (C) Cavitating neural tube and notochord forming.(D)Lumens coalesce to form the central canal of the neural tube 特点:神经管由胚 胎内细胞组成的实心索 中空而成。 鸟类、哺乳类、两 Notochord 栖类动物胚胎的后部神 经管及鱼类胚胎的全部 (D) 神经管的形成采取此种 方式
Developmental Biology 2. Secondary Neurulation 特点：神经管由胚 胎内细胞组成的实心索 中空而成。 鸟类、哺乳类、两 栖类动物胚胎的后部神 经管及鱼类胚胎的全部 神经管的形成采取此种 方式