鑑定Him基因於果蠅心臟發育的功能

Abstract

動物發育過程中，心臟是第一個有功能器官。生理上，心臟提供血液循環全身的動力，因此心臟是動物體最重要的器官之一，撇開形態上的差別，果蠅的心臟發育，在許多方面與脊椎動物的心臟發育是相似的，例如：兩者的心臟皆由中胚層衍生，參與控制心臟特化及分化的基因在不同物種間具有高度的演化保守性，如轉錄因子： tinman，gata4，mef2在果蠅及哺乳動物心臟發生的過程中表現的類似型態及相似功能。其中Homeobox gene tinman最為重要，tinman的突變果蠅，沒有背血管先驅細胞產生，也就是說不會有心臟的產生，在不同物種中如老鼠、青蛙、魚也找到與tinman相似的NKX2 group基因，且這些同源基因在心臟的發育上也扮演不可或缺的角色。研究顯示tinman籍由許多下游或平行基因的協同作用執行其在心臟發育的功能，而進一步探討這些基因間的相互關係，有助吾人對心臟發育全面的瞭解。本研究的主要目的在進一步分離更多與心臟發育有關的基因並闡明其在心臟發育的角色，籍由果蠅基因體計畫網站所提供的平台（Berkeley Drosophila Genome Project: Patterns of gene expression in Drosophila embryogenesis），我們鑑定出一個與心臟發育有關的候選基因Him，相較於tinman，Him略晚表現於中胚層為，晚期侷限於心臟與tinman相同，由於tinman為果蠅心臟發育上所必需的基因，him 與tinman 在表現形態的關係是否也反應兩者在心臟發育拌演的角色，則為本研究所要探討的問題。利用原位雜合（In situ hybridization）我們詳細確認Him表現於心肌及圍心細胞，以心臟特異性的分子標誌染色，我們發現 Him 功能缺失的果蠅突變株心肌細胞會增多，這樣的性狀也同樣的以RNAi的轉殖果蠅株得到証實，相反的在Him的功能獲效之果蠅株中，心肌細胞則增多。此外由啟動子的研究當中，我們確認了Him在中胚層的表現子，也証實其在中胚層的表現是受到Tinman、Pannier及Dmef2發育特定基因的調控。Abstract During animal embryogenesis, heart is the first funtional organ to be formed. Heart provides pulsative power for circulation of blood cells, therefore, heart is considered as one of the most important organs in animal. Despide the morphological difference, cardiogenesis in both Drosophila and vertebrates are quite similar. For instance: hearts of both fly and vertebrates are derived from mesoderm. Furthmore, most genes involved in cardogenesis, such as tinman, gata4 and mef2, are evolutionary conserved in different species. The homeobox containing gene, tinman plays a vital role in developing heart. The heart precursor cells are missing in tinamn mutant embryos, which leads to abolish of the mature heart. Tinman homologs, Nkx 2 group genes, were also discovered in dirrerence organisms, including mouse, Xenopus and Zerbra fish, which shown to play essential roles during heart development. Acummulate evidences suggested that tinman exerts its function by activating down-stream genes or acting synergistically with other genes to specify different cardial cell types. Disseting the interaction of these genes will assist us greatly in understanding the cardiogenesis of aninmals. The major objective of this study is to identified more cadiogenic genes, and elucidate their fndtion during heart development. From the platform of gene expression in Drosophila which is provided by Berkeley Drosophila Genome Project, we have identified a candidate gene, him, that may participate in heart development of Drosophila. Expression of Him in mesoderm is later than that of tinman. Later both tinman and Him are expressed restrictly in heart. As tinman is an essential gene in heart morphogenesis, we would like to address whether Him and tinman plays same roles as suggested by their expression profiles in this study. Using in situ hybridization we have found that Him is expressed in cardial and pericardial cells. Numbers of cardial cells are increased in loss-of-funtion embryos of Him. Similar phenotypes had been observed in him RNAi transgenic flies. In addition, we have characterized the mesoderm enhancer of Him and demonstrated that Him is regulated by tinman, pannier and Dmef2. Further studies are needed to show if Him is a direct target of these gene.