果蠅合子基因組啟動與胚胎多潛能分子機制之探討;Explore the molecular mechanism of Zelda in Drosophila zygotic genome activation and embryonic pluripotency

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Title:	果蠅合子基因組啟動與胚胎多潛能分子機制之探討;Explore the molecular mechanism of Zelda in Drosophila zygotic genome activation and embryonic pluripotency
Authors:	粘仲毅
Contributors:	國立中央大學生命科學系
Keywords:	胚胎發育;表觀遺傳;合子基因體啟動;基因調控;母代合子過渡;核小體佔據;胚胎多能分化性;;embryogenesis;zygotic genome activation;gene regulation;epigenetic;maternal-to-zygotic transition;nucleosome occupancy;embryonic pluripotency;Zelda;ehancer
Date:	2018-12-19
Issue Date:	2018-12-20 11:28:44 (UTC+8)
Publisher:	科技部
Abstract:	多數的動物受精卵發育初期，基因體幾乎保持在不表達的狀態，直到Maternal-to-zygotic transition，才開始活化，並主導胚胎的發育。我們在先前的研究中，以果蠅為動物模式，發現了第一個胚胎初期發育的重大轉錄因子Zelda(Zld)，透過與特定DNA序列模組結合，集體但有選擇性的活化子代基因體(Liang, et al., 2008)。當我們和其他研究團隊分別進行Zld的ChIP-Seq及大數據分析，發現Zld在果蠅胚胎中，有數以千計的核酸結合位點，並且與其他21個重要的早期轉錄因子的結合位點，及低密度核小體佔據是否足以引發果蠅細胞之染色質重組及有很高的關聯性(Sun, et al., 2015)。顯示Zld除了有能力直接活化基因，並具備先驅因子的作用模式，這類因子有能力進入並結合緊閉的染色質，調控染色質可及性，進而全面性的影響基因表達。 Zld的分子作用機制為何，又如何具備二元功能，尚待研究。因此在本研究中將進一步斛析Zld功能性結構，並發掘Zld共同作用因子，期將有助於了解Zld之二元作用模式。此外，脊椎動物的胚胎細胞在ZGA的同期，會經歷短暫的多能分化性時期，近似幹細胞的特性(Tadros & Lipshitz, 2009)，並伴隨著染色質結構的重組 (Vastenhouw, et al., 2010)。目前研究顯示有一組多能分化性因子(Nanog, Oct4 和 SoxB1)在纖維母細胞再程序化中，可能以先驅因子的方式引發細胞轉型成為幹細胞 (Souti, et al., 2012)。近期更進一步發現，他們在斑馬魚的同源基因，扮演類似Zld的角色活化ZGA (Lee, et al., 2013; Leichsenring, et al., 2013)。綜合上述，利用少數因子透過調節染色質的結構以活化子代整體基因組，同時建立胚胎之多能分化性，可能是保守的生物胚胎發育策略。因此在本研究計劃因此在本研究計劃中，將繼續研究Zld如何影響如何影響果蠅細胞的染色質重組，並測試是否是否足以引發多能分化性，從而對表觀遺傳、ZGA與胚胎多能分化性本研究為期三年，具體目標包含：(1) 測試 Zld是否足以引發果蠅細胞之染色質重組及多能分化性。(2) 解析Zld功能性結構，並定位其分別活化與降低核小體佔據之物理片段。(3)發掘可能分別負擔二元作用之合作因子 ;Almost in all animals, embryonic genome expression remains quiescent until the maternal-to-zygotic transition (MZT). During MZT, thousands of early zygotic genes are transcribed (zygotic genome activation, ZGA), along with the degradation of major maternal components. We previously identified a transcription factor, Zelda, which collectively and specifically activate zygotic genome through recognize the CAGGTAG-related motifs (Liang, et al., 2008). This is the first identified master regulator of ZGA. Extensive analysis of Zelda binding profile from us and others suggested that Zelda binds to thousands of loci, with a pattern correlated to high occupancy of early transcription factors and reduced nucleosome occupancy (Harrison, et al., 2011; Nien, et al., 2011; Sun, et al., 2015). This suggested that, in addition to direct activation, Zelda acts in a way similar to the concept of pioneer factors, which can bind to closed chromatin and regulate chromatin accessibility. However, the underlying molecular mechanism of Zelda remains unclear. Dissection of the functional domains of Zelda protein and identification of Zelda co-factors will help to further understand the dual function (direct activator and pioneer factors) of Zelda. Furthermore, it has been shown that vertebrate embryonic cells undergo a short pluripotent period, coinciding with ZGA (Tadros & Lipshitz, 2009), whereby the chromatin signature is established (Vastenhouw, et al., 2010). However, their relationships require more examination. Interestingly, a group of pluripotency factors, Nanog, Oct4 and SoxB1 family essential for fibroblast reprogramming were implicated to function as pioneer factors in introducing stem cells (Soufi et al., 2012). More recently, the orthologs of these factors were shown to initiate the first wave of ZGA in zebrafish (Lee et al., 2013; Leichsenring et al., 2013). Taken these together, it seems that the strategy of using one or a few factors to globally active early zygotic genome through modifying the chromatin landscapes could be a conserved strategy in ZGA and establishing embryonic pluripotency. In my study, I will test whether Zelda is sufficient to induce pluripotency in fly cells and explore the association between epigenetic modifications and embryonic pluripotency. Specific Aims include: (1) To test whether Zelda is sufficient to induce the pluripotency in Drosophila cells. (2) To dissect Zelda functional domains. (3) To identify potential cofactors of Zelda.
Relation:	財團法人國家實驗研究院科技政策研究與資訊中心
Appears in Collections:	[Department of Life Science] Research Project

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