利用Cullin 4b基因剔除小鼠研究Cullin 4b 在胚胎發育及智能遲緩的角色

Utilization of Cullin 4b knockout mice to study the role of Cullin 4b in embryonic development and mental retardation

陳軍宇(Chun-Yu Chen)

指導教授 ： 林淑華

國立臺灣大學/醫學院/醫學檢驗暨生物技術學研究所/博士(2012年)

https://doi.org/10.6342/NTU.2012.03408

摘要

在真核細胞中，蛋白質的降解系統主要作用於清除受損或是不需要的蛋白來維持細胞的正常生理。蛋白質降解受到嚴密的調控，以免對細胞內正在執行正常生理功能的蛋白造成損害。泛素 (ubiquitin) 為在真核細胞物種之間具備高度同源性的小分子蛋白。當細胞需要降解特定蛋白時，會利用一組特別的酵素系統將泛素連接到目標蛋白上。一旦目標蛋白重複被接上泛素而形成泛素鏈後，26S蛋白酶體會辨認出具有泛素鍵的蛋白將其分解。泛素連接到目標蛋白上需要靠泛素連結酶 (ubiquitin ligase, E3) 在正確的時間地點將泛素連結到目標蛋白上使其被26S蛋白酶體所分解。在真核細胞中眾多的泛素連結酶中，cullin蛋白為其中最大的家族。Cullin 4b (Cul4b)是cullin 家族的成員之一，位於X染色體上。在人類中，CUL4B基因突變後會導致X染色體遺傳性智能遲緩(X-linked mental retardation)。
本論文以條件式基因剔除策略，用不同的Cre基因轉殖小鼠建立Cul4b基因剔除小鼠來研究Cul4b的生理功能。利用Prm1-Cre基因轉殖小鼠來剔除Cul4b基因時，發現Cul4b基因剔除小鼠在胚胎發育早期便會死亡，顯示Cul4b基因對於胚胎發育的重要性。當利用Sox2-Cre基因轉殖小鼠在越過胚胎發育早期的時間點(第6.5~7.5天)後才剔除Cul4b基因時，此Cul4b基因剔除小鼠能夠存活。但此小鼠在經過動物行為測試及海馬迴神經樹突複雜度的測量後證實Cul4b基因剔除小鼠有智能遲緩的特徵。研究上述兩種Cul4b基因剔除小鼠的致病機制後，可以幫助我們了解Cul4b在胚胎發育及智能遲緩中所扮演的角色。

關鍵字

泛素 ； 泛素連結酶胚胎發育 ； 智能遲緩

並列摘要

In eukaryotes, the main function of protein degradation system is to degrade damaged or unneeded proteins to maintain the normal cellular physiology. Protein degradation is rigidly controlled to avoid damaging the proteins which are executing normal biological functions in cell. Ubiquitin is a small protein which is highly conserved among eukaryotic species. When specific proteins are needed to be degraded, ubiquitin will be covalently ligated to targeted protein via specific enzyme systems. Once the targeted proteins are ligated by ubiquitin repeatedly to form a poly-ubiquitin chain, 26S proteasome will recognize the targeted proteins which are labeled by poly-ubiquitin chains and then degrade them. The ligation of ubiquitin to targeted proteins and recognition of 26S proteasome in the appropriate time and space needs E3 ubiquitin ligases. Among a large amount of E3 ligases in eukaryotes, cullin proteins are the largest family. Cullin 4b (Cul4b) located on X chromosome is one of the members in cullin family. In human, mutation in CUL4B results in X-linked mental retardation.
This dissertation describes the conditional knockout strategy by using different Cre transgenic mice to study the biological function of Cul4b. Deletion of Cul4b by Protamine-1-Cre transgenic mice leading to early embryo lethal suggests that Cul4b plays an important role in mouse embryo development. When the Sox2-Cre transgenic mice are used to delete Cul4b beyond the time of early embryonic development (E6.5 to E7.5), Cul4b knockout mice are viable. Characterization of Cul4b knockout mice through behavioral test and examination of dendritic complexity demonstrate that Cul4b knockout mice represent the mental retardation syndrome. To study the pathogenic mechanism of two Cul4b knockout mice mentioned above helps us to understand the important role of Cul4b in embryonic development and mental retardation.

並列關鍵字

ubiquitin ； E3 ligase ； embryogenesis ； mental retardation

參考文獻

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