Delta/Notch訊息傳遞對海膽雛體初始管足發育的必要性

Abstract

棘皮動物門如海膽以成體具有獨特的五輻對稱性為人所知，但其實他們皆是從兩側對稱的幼生發育而來。在海膽中，五輻對稱性最早展現在幼生左側一個叫雛體 (adult rudiment) 的構造，但目前仍不知其背後形成的分子機制。先前在加州紫海膽 (Strongylocentrotus purpuratus) 中轉錄體分析發現部分參與Delta/ Notch 訊息傳遞的基因在幼生左側有較高的表現，因此我在此研究中進一步的了解Delta/Notch訊息傳遞在海膽雛體發育過程中的作用為何。我透過原位雜交實驗 (in situ hybridization) 釐清SpDelta、SpNotch、和SpHes和SpHet1基因在雛體中的表現，並發現以DAPT抑制Notch訊息傳遞會使雛體的初始管足 (primary podia) 構造無法正常發育。此外，為了瞭解雛體發育在演化上保守的分子機制，我比較加洲紫海膽和彩繪海膽 (Lytechinus pictus) 的雛體相關轉錄體，發現FGF、Wnt 以及 Notch 訊息傳遞路徑中的多個基因在兩物種中皆呈現差異性表現，顯示這些訊息途徑皆可能參與雛體發育的調控。最後，我確認 Notch 訊息傳遞的功能及其表現模式在彩繪海膽中具有保守性。綜合以上結果，本研究證實 Delta/Notch 訊息傳遞在海膽雛體形成過程中為初始管足發育所必須，並為理解棘皮動物雛體發育的分子機制提供了新的見解。

Echinoderms, such as sea urchins, are unique in possessing pentaradial symmetry as adults, despite developing from bilaterally symmetric larvae. In sea urchins, this transition first appears in the formation of the adult rudiment on the larval left side. However, the molecular mechanisms underlying rudiment development remain poorly understood. Preliminary transcriptomic analysis in Strongylocentrotus purpuratus revealed left-sided enrichment of several Delta/Notch signaling components, prompting further investigation into the role of this pathway. In this study, I examined the spatial expression of SpDelta, SpNotch, SpHes, and SpHey1 in rudiments using whole-mount in situ hybridization (WMISH), and demonstrated that Notch signaling inhibition via DAPT treatment disrupts primary podia formation. To explore evolutionary conserved regulatory programs, I analyzed rudiment-associated transcriptomes in S. purpuratus and Lytechinus pictus. Comparative analyses revealed differential expression of genes in the FGF, Wnt, and Notch pathways, suggesting their involvement in rudiment formation. Finally, I confirmed that Notch signaling function and expression patterns are conserved in L. pictus. These findings highlight Delta/Notch signaling as a key regulator essential for primary podia formation in sea urchin larvae and provide new insights into the molecular basis of rudiment development in echinoderms.