二枚貝におけるボディプラン進化機構の解明

阐明双壳类身体规划进化机制

• 批准号: 10J00511
• 负责人: 栗田 喜久
• 金额: $ 0.9万
• 依托单位: University of Tsukuba
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for JSPS Fellows
• 财政年份: 2010
• 资助国家: 日本
• 起止时间: 2010 至 2011
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-10J00511/
• 关键词: 軟体動物; 胚発生; 進化発生学; dpp; 遺伝子機能阻害; 卵割; 形態進化; 比較発生

軟体動物は極めて多様な外部形態を有する分類群であり、そのボディプランは「貝殻」の形に大きな影響をうける。しかしこれまで貝殻の形態を決定する発生プロセスに関する知見はほとんどなかった。そこで本研究では「2枚の殻」という特異的な殻形態を有する二枚貝の殻、および2枚の殻を機能的に利用するための筋肉の形成機構を明らかにし、二枚貝がカサガイ型の祖先から進化する際に生じた発生プロセスの変更の解明を試みた。二枚貝の殻形成については、二枚貝特有の卵割パターンでつくられるXL、XRと呼ばれる2つの割球の発生運命を、蛍光色素による細胞標識により追跡した。その結果、XLとXRは貝殻分泌腺の始原細胞であり、それぞれが貝殻分泌腺に分化することで、二枚貝では2つの貝殻分泌腺が形成されることが明らかになった。また先行研究から貝殻形成への関与が示唆されていたdpp遺伝子について、RNAiおよびモルフォリノオリゴによる機能阻害実験を行った結果、2枚の殻を分ける非石灰化領域「蝶つがい」の形成が阻害された。dpp遺伝子はカサガイでは貝殻の分泌に関与することが示されており、二枚貝ではdpp遺伝子が「蝶つがい」の形成という新規機能を獲得したことが示唆される。以上の結果から、二枚貝の「2枚の殻」の形成には(1)2つの貝殻腺始原細胞をつくる卵割パターンの変化、および(2)dpp遺伝子の機能的革新による「蝶つがい」の獲得、という2つの発生プロセスの変更が重要であったと考えられる。次に2枚の殻を閉じるための新奇筋肉「閉殻筋」の形成プロセスを、筋肉マーカー遺伝子をもちいた遺伝子発現解析で記載した。その結果、中胚葉細胞が筋肉へと分化する際に、他の軟体動物でもみられる牽引筋の原基の一部が、蝶つがいの方向へ分離し、その細胞集団が閉殻筋へ分化する様子がみられた。この結果は、「閉殻筋」と「蝶つがい」という2つの新奇形質形成機構の間に何らかのクロストークの存在を示唆する。

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