腸神經系統(enteric nervous system, ENS)是由大量神經元和神經膠質細胞聚集而成的最複雜的周圍神經系統。這些腸道的神經元和神經膠質細胞來源于迷走神經脊和骶神經脊細胞，在胚胎發育過程中，這些神經脊細胞沿著腸道移動最終占滿整個腸道。儘管神經脊細胞的遷移對於腸道神經系統的形成及功能的正常發揮起到很重要的作用，然而影響神經脊細胞遷移的分子機制的研究卻相對較少。因此找出參與調控神經脊細胞遷移的基因對於更好的瞭解腸道神經脊系統的發育起到非常重要的作用，並且為治療腸道神經系統紊亂所導致的相關疾病提供治療靶點。 / 本研究論文是由兩部份實驗課題所組成來研究影響腸和調控道神經脊細胞遷移及腸道神經系統發育的相關基因。第一部份課題主要研究的是Semaphorin3A (Sema3A)對於骶神經脊細胞遷移的影響。本論文的研究發現Sema3A不僅被腸道內的上皮細胞所表達，腸道兩側的盆神經節周圍的間質細胞也表達Sema3A。同時Sema3A的受體neuropilin-1被骶神經脊細胞所表達。體外培養的實驗表明Sema3A能夠抑制骶神經脊細胞的遷移。另外，當表達Sema3A的腸道末端與骶神經脊細胞共同培養時，骶神經脊細胞的遷移同樣也受到抑制。這些研究結果表明由腸道末端的上皮細胞和腸道外圍的間質細胞所表達的Sema3A共同作用來調控骶神經脊細胞在停滯時期的遷移活動。 / 第二部份的研究課題主要研究的是轉錄因子Sox10以及其靶基因對於迷走神經脊細胞遷移的影響。Dominant megacolon (Dom)是一種攜帶有Sox10突變的巨結腸癥小鼠模型。本研究利用這種小鼠模型來發現突變鼠中可能影響迷走神經脊細胞遷移的基因。從迷走神經脊細胞體外培養發現： 由於Sox10突變，迷走神經脊細胞在體外培養24小時后，細胞遷移延遲，細胞的分化能力被改變，並且細胞死亡增加。利用基因芯片的方法比較了純和變異鼠迷走神經脊細胞和正常鼠迷走神經脊細胞的基因表達的差異。螢光素酶報告基因分析顯示，Sox10可以結合Lama4, Itga4和Gfra2的啟動子并激活它們的表達。 Sox10能與Gfra2啟動子上-116bp到-58bp之間序列的結合誘導Gfra2的表達。在純和變異鼠迷走神經脊細胞中，通過上調Gfra2信使RNA的表達，細胞死亡的數目大大下降，表明Gfra2作為Sox10的靶基因，對迷走神經脊細胞的存亡有著重要作用。 / 綜上所述，我們發現在骶神經脊細胞未進入腸道末端的這段停滯期內，Sema3A對於骶神經脊細胞的遷移起到抑制作用，Sema3A通過其表達在這段停滯期內的時空改變來調控骶神經脊細胞進入腸道。另外我們發現由於Sox10的突變，迷走神經脊細胞表現出非正常的遷移和基因表達的變化。作為Sox10的靶基因，Gfra2對於迷走神經脊細胞的死亡有重要的作用。 / The enteric nervous system (ENS) is the most complex part of the peripheral nervous system which is composed of a vast number of neurons and glial cells. The enteric neurons and glial cells arise from vagal and sacral neural crest cells (NCCs) which migrate along the gastrointestinal tract to colonize the whole gut during the embryonic development. The molecular mechanisms regulating the NCC migration are poorly characterized despite the importance of this migration process in the ENS formation. Therefore, identification and characterization of molecules involved in the modulation of NCC migration are essential to understand the ENS development and could provide potential therapeutic targets for the treatment of human ENS disorders. / The present study was aimed to identify and characterize the molecules involved in modulating the NCC migration during the ENS development, and was divided into two parts. The first part focused on semaphorin3A (Sema3A) signaling, Sema3A was found to be expressed in the hindgut epithelium and also the adjacent regions of pelvic ganglia, while its receptor, neuropilin-1, was expressed by sacral NCCs before sacral NCCs entered the hindgut. Sacral NCC migration and neuronal fiber extension in vitro were retarded in the culture medium containing Sema3A. When a hindgut segment expressing Sema3A was co-cultured with sacral NCCs, sacral NCC migration and neuronal fiber extension were also suppressed by the hindgut segment. These findings provide evidence for the repulsive activity of Sema3A before the entry of sacral NCCs to the hindgut. / The second part focused on the potential target genes of the transcription factor Sox10 which is expressed by migrating NCCs. A naturally occurring mouse mutant Dominant megacolon (Sox10Dom) which expresses a mutant Sox10 was used to identify candidate molecules which may possibly affect the NCC migration. After 24 hours in culture, vagal NCCs from Sox10Dom/Dom embryos showed retarded migration, abnormal cell differentiation and excessive cell death in vitro when compared to Sox10⁺/⁺ vagal NCCs. Results of microarray analyses revealed differentially expressed genes in Sox10Dom/Dom as compared to Sox10⁺/⁺ vagal NCCs after 24 hours in culture. Among these genes, Sox10 was able to bind to the promoter of Itga4, Lama4, and Gfra2 to induce their expression. Sox10 activated Gfra2 promoter by direct binding to the critical region located between -116bp and -58bp upstream of the Gfra2 transcription start site. Finally, re-expression of Gfra2 in Sox10Dom/Dom vagal NCCs resulted in decreased cell death, suggesting that down-regulation of Gfra2 in the mutant mice played an important role in early cell death of vagal NCCs. / In conclusion, before sacral NCCs entered into the hindgut, Sema3A inhibited the sacral NCC migration, and the spatiotemporal change of the Sema3A distribution regulated the entry of sacral NCCs into hindgut. Furthermore, retarded cell migration, abnormal cell differentiation, increased cell death and differential gene expression were found in Sox10Dom/Dom vagal NCCs as compared with those from Sox10⁺/⁺ embryos in vitro. The expression of Gfra2, a potential target gene of Sox10, promoted the cell viability of vagal NCCs. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Wang, Cuifang. / Thesis (Ph.D.) Chinese University of Hong Kong, 2014. / Includes bibliographical references (leaves 180-196). / Abstracts also in Chinese. / Wang, Cuifang.
| Identifer | oai:union.ndltd.org:cuhk.edu.hk/oai:cuhk-dr:cuhk_1077688 |
| Date | January 2014 |
| Contributors | Wang, Cuifang (author.), Chan, Wood-yee (thesis advisor.), Chinese University of Hong Kong Graduate School. Division of Biomedical Sciences, (degree granting institution.) |
| Source Sets | The Chinese University of Hong Kong |
| Language | English, Chinese |
| Detected Language | English |
| Type | Text, bibliography, text |
| Format | electronic resource], electronic resource, remote, 1 online resource (xi, 197 leaves) : illustrations, computer, online resource |
| Rights | Use of this resource is governed by the terms and conditions of the Creative Commons “Attribution-NonCommercial-NoDerivatives 4.0 International” License (http://creativecommons.org/licenses/by-nc-nd/4.0/) |
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