塞席爾果蠅抗辛酸基因之驗證

Abstract

塞席爾果蠅是唯一專食諾麗果的果蠅，而諾麗果對其他黃果蠅亞群卻是有毒的。之前的基因定位研究發現，塞席爾果蠅的第三號染色體當中有一段包含18個基因，長達169000 鹼基對的區域，與抵抗諾麗果主要的揮發成分辛酸有關。為了尋找影響辛酸抵抗能力的特定基因，我利用反轉錄聚合酶鏈鎖反應檢測塞席爾果蠅和其近源種，黃果蠅和擬黃果蠅。因為辛酸抵抗的能力在兩性皆存在，所以可以排除五個基因。利用hs-Gal4/UAS系統，分別在擬黃果蠅中，表現塞席爾果蠅的三個氣味結合蛋白（obp83cd, obp83ef和obp83g），發現這些轉基因果蠅都無法抵抗辛酸。我另外在黃果蠅中，分別降低與增加神經胜肽接受器(NPFR1)的基因表現，我發現增加神經胜肽接受器的表現，會降低黃果蠅對辛酸的抵抗力，但減少神經胜肽接受器基因表現量並沒有影響。這些結果顯示，塞席爾果蠅抵抗辛酸的能力，可能是由多個基因共同影響，或是由這次實驗沒有測試到的其他基因所造成。

Drosophila sechellia is the only species feeding on the Noni fruit, Morinda citrifola, which is toxic to the other Drosophila species. Previous genetic mapping indicated that a 169 kb D. sechellia genomic region spanning 18 genes on the third chromosome is responsible for resistance to the major toxic component, octanoic acid, of Noni fruit. To identify the candidate genes affecting octanoic acid resistance, I examined the expression patterns of 18 candidate genes in D. sechellia and two sibling species, D. melanogaster and D. simulans, by reverse transcription PCR. Because the octanoic acid resistance is shown in both sexes of D. sechellia, five genes were excluded to associate with the resistance. Over expression of three D. sechellia odorant binding protein (obp) genes namely, obp83cd, obp83e, and obp83g, in D. simulans by heat-shock Gal4 transgenes, does not increase the octanoic acid resistance. Moreover, I enhanced and reduced Neuropeptide F receptor (NPFR1) expression in D. melanogaster, respectively, and found that the NPFR1 overexpressed flies showed less resistance to octanoic acid than the wild type flies. The results suggest that octanoic acid resistance in D. sechellia might be contributed either by multiple genes or by the other candidate genes that were not investigated in this study.