Signal transduction that controls gene expressions in the adult rudiment of echinoderms

2018 Fiscal Year Final Research Report

• Project/Area Number: 16K07368
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Developmental biology
• Research Institution: Kanazawa University
• Principal Investigator: Yamaguchi Masaaki 金沢大学, 生命理工学系, 教授 (60182458)
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: 棘皮動物 / 五放射体制 / 成体原基 / 半索動物 / AP map gene / FGFシグナリング / Hox複合体

Outline of Final Research Achievements

Hemichordates and echinoderms are sister taxa of the Ambulacraria clade, and share tripartite larvae. Hemichordates inherit the body plan (proboscis-collar-trunk) from larvae. In contrast, echinoderms form a pentaradial body plan in the adult rudiment and metamorphose into juveniles. The evolution of this unique body plan of echinoderms still remains a mystery in zoology.
We isolated sand dollar orthologs of anteroposterior (AP) map genes that control ectodermal patterning along the AP axis in hemichordates, and examined their expression in the sand dollar. Solely orthologs of collar AP map genes were expressed in ectoderm of the adult rudiment, and their expression was restricted to the future ambulacral ectoderm. I propose that the evolution of echinoderms was accompanied by loss of the proboscis and trunk from a common ancestor, concomitant with radial outgrowth from the collar. Co-linear expression of Hox complex suggests adult mouth-anus axis may represent AP axis of echinoderms.

Free Research Field

進化発生学

Academic Significance and Societal Importance of the Research Achievements

棘皮動物の特異な体制の進化は未だ動物学の謎である。その進化を幼生の体腔プランからの変形として捉え、それを分子的に提示したことに学術的な意義がある。ギボシムシの襟外胚葉で発現する前後軸マップ遺伝子は、ウニ成体原基において水腔から伸長する放射水管を覆う歩帯外胚葉で発現する。襟外胚葉と歩帯外胚葉は幼生の相同な体腔を内包しているので、ウニの五放射の歩帯外胚葉とギボシムシの襟外胚葉は相同であり、棘皮動物の放射線は、歩帯動物共通祖先の前後軸の重複ではなく、半索動物翼鰓類の触手器官のような付属突起であることを示唆する。Hox複合体の共線的発現は、棘皮動物の前後軸は成体の口-肛門軸と考えられる。