Wnt/β-catenin訊息傳遞路徑對文昌魚胚胎發育之影響

Abstract

訊息傳遞路徑在基因調控中扮演關鍵的角色，進而影響胚胎各胚層的分化與發育。在後生動物中，Wnt/β-catenin訊息傳遞路徑決定體軸的調控以及胚層的分化。先前研究指出，若在受精後的文昌魚胚胎中過度啟動Wnt/β-catenin訊息傳遞路徑會使中胚層和內胚層擴張，並使外胚層消失。然而在此過程中整體基因的表現以及變化仍然未知。透過核糖核酸定序，我們分析了文昌魚胚胎發育過程中過度啟動Wnt/β-catenin訊息傳遞路徑對下游基因的影響。我們使用1-azakenpaullone（GSK-3β的小分子抑制劑）在胚胎一細胞時期到神經胚期（neurula stage）過度啟動整顆胚胎的Wnt/β-catenin訊息傳遞路徑。我們發現，中胚層與內胚層的標誌基因（marker gene）受到正調控，而外胚層的標誌基因則受到負調控。在基因集富集分析(Gene Ontology enrichment analysis) 中發現受到過度啟動Wnt/β-catenin訊息傳遞路徑影響的基因與Wnt、BMP、Nodal、FGF和Notch等訊息傳遞路徑相關；而受到負調控的基因則與外胚層的纖毛和神經元等組織相關，暗示外胚層的組織分化受到了抑制。我們觀察到，在胚胎發育過程中，內胚層和中胚層的標誌基因擴張，而外胚層的標誌基因則消失。然而，在部分胚胎中，中胚層與內胚層的基因並未表現，暗示在過度啟動Wnt/β-catenin訊息傳遞路徑後，中胚層與內胚層的形成可能受到其他訊息傳遞路徑的調控。本研究證實在早期胚胎發育期間過度啟動Wnt/β-catenin訊息傳遞路徑會影響許多調控體軸與胚層的訊息傳遞路徑，並使中胚層與內胚層擴張和外胚層消失。

Signaling pathways comprise an essential part of developmental gene regulatory networks. The activities of signaling pathways lead to changes of the gene regulatory states, and consequently determine different cell fates in particular areas within a developing embryo. In a wide range of metazoan animals, the canonical Wnt/β-catenin pathway has been implicated in playing important functions for defining the initial axes and specifying different germ layers of the embryo. Previous studies showed that Wnt/β-catenin signaling is active in the nuclei of vegetal hemisphere in early amphioxus embryos. Overactivation of Wnt/β-catenin signaling greatly expands mesoderm and endoderm at the expense of ectoderm. However, changes of global gene expression profile after overactivation of Wnt/β-catenin signaling pathway during amphioxus embryogenesis remain unclear. Here we use RNA-seq approach to globally examine developmental genes downstream of Wnt/β-catenin signaling pathway during amphioxus embryogenesis. We used 1-azakenpaullone, which is a small molecule inhibitor of GSK-3β, to globally activate Wnt/β-catenin signaling pathway in amphioxus embryos at one-cell stage to early neurula stage. Our results showed that germ layer marker genes in mesoderm and endoderm were up-regulated, while ectoderm marker genes were down-regulated. Genes involved in Wnt, BMP, Nodal, FGF and Notch signaling pathways were influenced; while genes related to ectoderm derived structures such as cilia and neurons were down-regulated, signifying ectoderm loss. Overactivation of Wnt/β-catenin signaling led to mesoderm and endoderm expansion, accompanied by the loss of ectoderm. However, in some inhibitor-treated embryos, mesoderm and endoderm genes were not expressed, suggesting that the formation of these germ layers might be regulated by other signaling pathways following the overactivation of the Wnt/β-catenin pathway. Overactivation of Wnt/β-catenin signaling pathway during early embryo development influenced genes in Wnt, BMP, Nodal, FGF and Notch signaling pathways, and led to mesoderm and endoderm expansion at the expense of ectoderm.