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Title: | 環節動物Xlox族同源區基因演化的探討 Evolution of Xlox family homeobox genes in Annelida |
Authors: | 石芝菁 |
Publication Year : | 2001 |
Degree: | 碩士 |
Abstract: | 同源區基因(homeobox gene)的表現與胚胎發育有關,且其同源區(homeobox)序列具有很高的保守性,所以常被用來研究演化發生學的課題。其中,Xlox族的同源區基因已被證實參與內胚層腸道分區的機制,由於此族基因在演化關係相差甚遠的環節動物(屬於原口類)和脊椎動物(屬於後口類)中均被發現,且參與內胚層腸道分區的機制也很類似,因此是研究各動物門內胚層腸道基本構造演化的良好題材。在環節動物門中,多毛綱是比蛭綱更原始的環節動物,且多毛綱動物的腸道沒有像蛭綱的嗉囊的複雜分化,因此可藉由比較多毛綱與蛭綱動物Xlox族同源區基因的序列,探討Xlox族同源區基因的演化與腸道構造演變的關係。 本研究利用PCR及GenomeWalker的方法,選殖出遊走活動的多毛綱動物腺帶刺沙蠶(Neanthes glandicincta)的Xlox族同源區基因,包含完整同源區在內、共長3405 bp的基因片段;及固著生活的華美盤管蟲(Hydroides elegans) Xlox族基因同源區的部分序列、長69 bp。將Xlox族基因同源區序列轉譯成的胺基酸序列和二種蛭綱動物及其他不同門類動物的序列,互相比對並進行親緣關係分析。結果顯示,環節動物的Xlox族基因不形成單系群(monophyleties),而是環節動物門多毛綱與海星、文昌魚成一群;另外蛭綱動物及脊堆動物各自成一群。這個結果顯示環節動物多毛類、棘皮動物和頭索動物等海生無脊椎動物的Xlox族基因同源區可能是較原始的序列,而環節動物水蛭和脊椎動物的Xlox基因同源區則發生了較多的改變。 Homeobox genes are important for establishing body plan and determining cell-type or cell-lineage throughout the metazoans. The homeobox genes of the Xlox family are essential for the early morphogenesis of the midgut region and cellular differentiation during embryonic development. Since homeobox sequences and expression patterns of Xlox family homeobox genes are highly conserved in organisms as diverse as leeches to vertebrates,these genes provide an excellent tool to study the evolution of endoderm-derived gut structure among animal phyla. In this study, I identified the homeobox sequences of Xlox family genes from two species of polychaete, Neanthes glandicincta and Hydroides elegans, using the GenomeWalker technique. Phylogenetic analyses of the Xlox homeodomain amino acid sequence show that there are 3 major clades: vertebrates, leeches, and a mixture of marine invertebrates, including amphioxus, starfish, and polychaetes. These results suggest that the Xlox homeodomain sequences of amphioxus, starfish, and polychaetes are more ancestral than those of vertebrates and leeches. Moreover,the Xlox homeodomain sequences of leeches evolved faster than that of polychaetes, implying that the complexity of the leech's gut structure may be related to the changes of the Xlox genes of the Annelida. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/75167 |
Fulltext Rights: | 未授權 |
Appears in Collections: | 漁業科學研究所 |
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