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標題: | Ran在斑馬魚視網膜發育的功能 Ran Functions in Retinal Development of Zebrafish |
作者: | Chien-Wei Lin 林建瑋 |
指導教授: | 蔡懷楨(Huai-Jen Tsai) |
關鍵字: | 斑馬魚,視網膜,胚胎發育, Ran,Arl6ip,zebrafish,retina, |
出版年 : | 2010 |
學位: | 碩士 |
摘要: | 在過去Ras-realated nuclear protein (Ran) 的研究主要探討如何透過tubulin排列影響細胞分裂以及核內外運輸的相關研究,但它在發育的過程中扮演的角色仍是未知。於是,我們利用斑馬魚在發育生物學上的優勢來研究Ran與眼部發育相關基因的表現情形。我們發現在原腸胚期前的斑馬魚胚胎中ran有全身性的表現,發育到咽期後則會局部表現在頭部、眼睛。若對斑馬魚胚胎注射Ran morpholino去knockdown Ran蛋白在胚胎的表現量,可以觀察到斑馬魚在眼睛及腦部的有顯著缺陷,例如會出現小眼症以及視網膜細胞無規則排列且無分化的情況。接著觀察眼部區域增生的情況,我們發現在ran-morphants中,眼部區域BrdU的signals會提早下降且細胞分裂的marker cyclinD1的表現也會提早降低,顯示細胞週期異常提早結束。在進行了TUNEL assay之後發現這些細胞不論早期(24 hpf) 或是晚期(72 hpf)都沒有異常細胞凋亡的訊號;同時我們也發現在ran-morphants中,視網膜細胞早期決定眼部區域的基因rx1及pax6的表現僅輕微降低,顯示這些在眼部區域中的細胞確實還是有特化成為視網膜前驅細胞。但是在觀察與視網膜發育相關基因的表現情形,發現ran-morphants視網膜分化中(48 hpf)、晚期的細胞其shh、six3a等視網膜細胞分化的基因不能正常地表現,且shh下游基因p57kip2也不會表現; 而HuC和neurolin視網膜神經元的表現蛋白質也都受到抑制,由此得知視網膜細胞未進行分化導致視網膜結構沒有出現。若利用deltaC觀察分化中、晚期這群沒有表現HuC和neurolin的細胞,發現deltaC沒有在眼部區域表現甚至連視網膜幹細胞的niche ciliary marginal zone也沒有表現,顯示這群未分化的細胞也不再是視網膜前驅細胞。說明在視網膜發育晚期這些視網膜細胞是處於沒有分裂但也沒有分化的狀態。進一步地偵測能決定最早出現的神經ganglion cell layer命運的proneural gene ath5,以及能決定amacrine cell和photoreceptor 命運的proneural gene neuroD的表現,發現ath5以及neuroD的表現大量地降低甚至有未開啟的情況。總結,當Ran蛋白缺失時,眼部區域早期有特化出視網膜前驅細胞,但由於細胞週期異常提早停止以及proneural genes 表現降低,影響視網膜細胞命運無法決定,進而影響中、晚期細胞無法分化,最後導致視網膜發育的異常。 Ras-realated nuclear protein (Ran) has been reported to be involved in cell division by modulating assembly of tubulin and regulating nucleocytoplasmic transport. However, the biological function of Ran in embryonic development is unknown. In this study, we take the advantage of zebrafish as an animal model in developmental biology to study the molecular mechanism that how Ran is involved in eyes development. Using whole mount in situ hybridization showed ran transcripts were ubiquitously expressed throughout the whole embryo before gastrula period, but restrictedly expressed in brain and eyes after the pharyngula. We injected the anitsense morpholino oligonucleotides (MO) into zebrafish embryos to specifically knockdown Ran translation, and observed defects in eyes and brain. Particularly, the occurrence of microphthalmos was extremely predominant, in which the order layers with differentiated retinal cells was not so pronounced as that in wild-type eyes. Furthermore, we observed both the BrdU signals and the expression of cyclinD1 were declined earlier in the eye filed in embryos injected with ran-MO, indicating that cell cycle exit in retina is defective in ran-morphants. No apoptotic signal in eye field was found either at early (24 hpf) stage or late (72 hpf) embryonic stage by TUNEL assay. The expressions of rx1 and pax6, which are markers of the eye field in early embryonic stage, were only slightly reduced in ran-morphants, indicating that the retinal cells of ran-morphants were mostly specified to neural progenitor cells. However, when we examined the expressions of some retinal differentiating genes such as shh, six3a and p57kip2, a gene down stream of shh, we found that these genes were not expressed in the ran-morphants either at middle (48 hpf) stage or late stage of retinal development. We also observed the retinal neuron proteins such as HuC and Neurolin were repressed. This line of evidences suggested that retinal cells in ran-morphants were undifferentiated, which leaded to failure of developing normal retinal structure. In addition, we found that there was no deltac expression in HuC- and neurolin-negative cells, even nor in ciliary marginal zone, indicating that these cells were no longer progenitor cells. In other words these cells were not only undifferentiated but also unproliferated at late stage. Furthermore, the proneural gene ath5, which is the first gene to determine the cell fate of developing ganglion cell layer, and neuroD, which is needed to determine the cell fate of amacrine cell and photoreceptor, were dramatically decreased or even unexpressed in retinae of ran-morphants. Taken together, we concluded that the loss of Ran function causes the decrease expression of proneural genes, resulting in the cell fate of retinal cells are not determined to go further differentiate in the middle and late developmental stages, which in turn, the retinal development is disrupted, although the eye field can perform specification and process to retinal progenitor cells in early developmental stage. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/22496 |
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顯示於系所單位: | 分子與細胞生物學研究所 |
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