鳥類のゲノムサイズと構造の起源は,鳥類以外の恐竜に由来する
Chris L Organ1, Andrew M Shedlock, Andrew Meade
1Museum of Comparative Zoology, Harvard University, 26 Oxford Street, Cambridge, Massachusetts 02138, USA. corgan@oeb.harvard.edu
Nature
|March 9, 2007
まとめ
小型の鳥類のゲノムは,鳥類の数百万年前にサウリスキア恐竜で進化した. これは,縮小された繰り返しDNAのような重要な鳥類の特徴が,鳥だけでなく,非鳥類の恐竜から生まれたことを示唆しています.
科学分野:
- 進化生物学の進化生物学について
- パレオゲノミクスとは
- 比較ゲノミクスとは
背景:
- 鳥類のゲノムは,他のアムニオットと比較して著しく小さく,効率化されており,反復性および非コーディングDNA要素が少なくなります.
- この簡素化されたゲノムは,飛行のための適応であり,大きなゲノムと細胞サイズに関連する代謝コストを削減すると仮定されています.
- 絶滅した種からのゲノムデータの希少性のために,ゲノム進化の研究は困難です.
研究 の 目的:
- 小型の鳥類のゲノムサイズの進化的起源を調査する.
- 絶滅した鳥類を含む絶滅した恐竜のゲノムサイズを,新しい比較方法を用いて推定する.
- 鳥類のゲノムに特徴的な繰り返しのDNAの減少が,恐竜の進化においていつ起こったかを決定する.
主な方法:
- 骨細胞の大きさを,現在存在する脊椎動物におけるゲノムサイズと相関させるための新しいベイジアン比較方法を利用した.
- この確立された関係を適用して,31種の絶滅した恐竜のゲノムサイズを推定しました.
- 絶滅した恐竜の系統における全ゲノムに散らばった移動要素の割合を推定するために,比較ゲノムデータを分析した.
主要な成果:
- この研究は,鳥類の飛行適応に特有の小さなゲノムが,2億3000万年から2億5000万年前のサウリスキア恐竜の系統で進化し,最初の鳥より先行したと推定しています.
- オーニチスキー族の恐竜は,かなり大きなゲノムを有していたと推論されており,恐竜類の祖先の条件を表している可能性が高い.
- 繰り返しのDNA (間隔の移動要素) は,オルニチスキアの恐竜 (7~19%) と比べて,サウリスキアの恐竜の全ゲノムのより小さな部分 (5~12%) を構成しており,前者の活動が低下していることを示しています.
結論:
- 鳥類の飛行に関連したゲノム精度化は,鳥類の進化よりずっと前に,非鳥類のサウリスキア恐竜に由来しました.
- この発見は,羽毛や高度な呼吸器系など,非鳥類の恐竜で進化した特徴のリストに,ゲノム特性を追加するものである.
- サウリスキアにおける重複要素の活動が低下することは,コンパクトな鳥類のゲノムに向けた重要な進化的ステップを意味する.
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