Horizontal gene transfer of a vertebrate vasodilatory hormone into ticks

2018 Fiscal Year Final Research Report

• Project/Area Number: 16K15264
• Research Category: Grant-in-Aid for Challenging Exploratory Research
• Allocation Type: Multi-year Fund
• Research Field: Parasitology (including sanitary zoology)
• Research Institution: Tokyo Medical and Dental University (2017-2018); Mie University (2016)
• Principal Investigator: IWANAGA Shiroh 東京医科歯科大学, 大学院医歯学総合研究科, 教授 (20314510)
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: マダニ / 進化 / 遺伝子水平伝播

Outline of Final Research Achievements

In this study, we conducted the genomic analysis of Ornithodoros moubata and indicated that salivary vasodilator molecule, tick adrenomedullin (TAM), was transferred horizontally from host animals. This analysis showed that exons 1 and 2 of TAM were derived from exon 2 and 4 of vertebrate adrenomedullin. Interestingly, the exon3 which is not responsible for vasodilating activity of vertebrate adrenomedullin was completely disappeared from tick’s genome. In contrast, the structure of exons 2 and 4 are completely conserved between TAM and vertebrate adrenomedullin. These results indicated that the essential genomic structure are never changed, but the non-essential structure rapidly disappeared. The TAM is probably essential for the survival of ticks, and thus this would be a selective pressure during evolution.

Free Research Field

寄生虫・衛生動物学

Academic Significance and Societal Importance of the Research Achievements

通常、生物において遺伝情報は親から子へと受け継がれていく（遺伝子垂直伝播）。この過程で遺伝子に様々な変異が加わり、生物は漸次的に進化していく。一方、時として個体間や異種生物間で遺伝情報が偶発的に受け渡されることがあり、これを遺伝子水平伝播と呼ぶ。これまで多細胞生物においては遺伝子水平伝播が発見されておらず、その進化への影響が不明であった。本研究では宿主動物と外部寄生体（マダニ）間で遺伝子水平伝播が起こったことを証明し、その結果、新たな属の出現につながった可能性を示唆した。この成果は進化における遺伝子水平伝播の新たな意義を示すと考える。