海綿動物是多細胞動物當中結構最簡單、形態最原始的一類。其細胞已經分化，但是還沒有形成組織和器官。海綿動物的分布及生存的棲地非常廣泛，多數種類發展出各種特殊的禦敵策略來適應環境。近年來學者們發現海綿含有一些特殊化學產物，有些醫學研究正以其特性發展抗癌藥物。然而我們對於海綿動物的生物學及生物多樣性的瞭解仍然非常缺乏。尤其是在海綿的分類上，依照傳統的型態來分類已到達了瓶頸。因此本研究利用Long PCR以及Primer walking得方式定序出澳洲球形海綿Cinachyrella australiensis的粒線體DNA，除了可供建立海綿的DNA資料庫協助海綿分類，並可以更進一步了解海綿的演化及親緣關係。澳洲球行海綿的粒線體總長為19444個鹼基對，其包含14個蛋白質基因，2 個核醣核酸基因(rRNA)，以及24個傳遞者核酸基因(tRNA)。本研究在此海綿上發現一些獨特的特徵，包括在粒線體DNA 細胞色素氧化脢次單元一(COI)之序列中發現有一intron的序列，及一種存在於植物、真菌及原生生物粒線體或動物細胞核中的蛋白質基因ATP9，在本研究中被發現存在於海綿粒線體中，及在海綿粒線體上的tRNA二級結構非常相似於細菌的結構，而異於一般無脊椎動物的結構。由以上證據顯示，後生動物的粒線體DNA 的分子量大小是與演化成反比。

Sponges (Porifera) are the most primitive multicellular animals that are highly diverse and complex associated with other organisms, microbes especially. Recently, sponges have received a lot of attention as they are a rich source of nature products with antiviral, antitumor, and antimicrobial activities. Sponges play such important roles in so many marine habitats but little is known about their diversity, biology and ecology as compared with most other animal groups. Moreover, due to limited information provided based on morphology, other method of classification is need. Mitochondrial DNA sequence may fulfill such purpose. The complete nucleotide sequence (19444 bp) of the mt genome of the Cinachyrella australiensis (Demospongiae: Spirophorida) was determined. The genome contains the two rRNA, 24 tRNA and 14 protein-coding genes. We found that poriferan mtDNAs resemble those of other animals in their compact organization, and a well-conserved animal-like gene order. However, this molecule has several unique features: the ATP 9 gene is the first found to be present in the mt genome of multicellular animals, the cytochrome c oxidase subunit I (COI) gene include a group I intron, and encode bacteria-like tRNA. The results represent that the evolution of metazoan mtDNA has been a multistep process to the reduction of tRNA and the introduction of multiple changes of the translation code.

Contents


Introduction………………………...……………..1
Materials and Methods……………………………8
Results…………………………………………...15
Discussion……………………………………….26
Reference………………………………………..32
Tables……………………………………………42
Figures…………………………………………..47
Supplementary…………………………………..77

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