臺灣海域瓶鼻海豚（Tursiops truncatus）第二型主要組織相容性複合體DQB基因之序列變異

Sequence Variation of MHC Class II DQB Gene in Bottlenose Dolphin (Tursiops truncatus) from Taiwanese Waters

主要組織相容性複合體（MHC）為一多基因家族，其轉譯之蛋白質於脊椎動物免疫反應的啟動扮演重要的角色。為了更了解繁衍興盛的海洋哺乳類之免疫多樣性，我們採集42隻瓶鼻海豚（Tursiops truncatus）分析其MHC DQB基因座中第二外顯子之序列變異。增幅之序列長為172個鹼基對，且每一個個體僅有一至兩條序列。高比例的非同義核酸取代與中等程度的變異暗示此基因座受到正向選汰壓的影響，而此現象反駁了海洋環境選汰壓較低的說法。瓶鼻海豚與其他鯨類DQB第二外顯子序列之系統發生關係與其分類關係並不吻合，顯示這裡出現跨物種演化模式。

The major histocompatibility complex (MHC) is a large multigene coding for glycoproteins that play a key role in the initiation of immune responses in vertebrates. For a better understanding of the immunologic diversity in thriving marine mammal species, the sequence variation of the exon 2 region of MHC DQB locus was analyzed in 42 bottlenose dolphins (Tursiops truncatus) collected from strandings and fishery bycatch in Taiwanese waters. The 172 bp sequences amplified showed no more than two alleles in each individual. The high proportion of non-synonymous nucleotide substitutions and the moderate amount of variation suggest positive selection pressure on this locus, arguing against a reduction in the marine environment selection pressure. The phylogenetic relationship among DQB exon 2 sequences of T. truncatus and other cetaceans did not coincide with taxonomic relationship, indicating a trans-species evolutionary pattern.