Wnt 傳導路徑在果蠅神經元樹突修剪之調控

Abstract

樹突修剪為演化保留中一項神經重塑過程，神經元會藉此消除原先的突觸以完善新的神經迴路，此現象亦發生在果蠅變態過程的感覺神經元。先前的 RNA 干擾篩選中，我們發現當果蠅感覺神經元表現 dishevelled (dsh)雙股 RNA 時，會產生 樹突修剪的缺陷。而 dsh 是多個 Wnt 傳導路徑上中心分子，對於發育、再生、抑 或是神經發生而言皆不可或缺;然而 Wnt 傳導路徑是否參與在樹突修剪的調控仍屬未知。 dTCF 為特定存在 Wnt 經典傳導路徑下游的轉錄因子，藉由顯性抑制突變的 dTCF 的表現，我們證實了果蠅感覺神經元的樹突發育及修剪皆需要 dTCF 的作用。 在其他突變檢測中，我們認為 Frizzled 及 Arrow 是作為果蠅感覺神經元上 Wnt 傳導路徑的受體，以調控其樹突修剪。此外，當 Wnt 經典傳導路徑的負調控者 Axin 過度表現時，神經元的樹突修剪亦受到干擾。以持續表現活性之 β-catenin 救援神經細胞後，持續激活 Wnt 經典傳導路徑，受到 dsh 雙股 RNA 或 Axin 過度表現擾動的果蠅感覺神經元因而成功完成樹突修剪。以上，證實了Wnt 經典傳導路徑在 神經樹突修剪中扮演不可或缺的腳色。

Dendrite pruning is a conserved neuronal remodeling process, during which neurons would eliminate their dendrites to rectify neural connectivity. From our previous RNAi screening for the regulators of dendrite pruning in Drosophila sensory neurons, we observed pruning defects in the expression of dishevelled (dsh) double-stranded RNA. Dsh is the center molecule in multiple Wnt signaling essential for development and tissue regeneration, as well as neurogenesis; however, whether Wnt signaling modulates dendrite pruning remains unknown. By overexpressing the truncated transcription factor specific in Wnt canonical pathway, dTCF-∆N, we demonstrate that dTCF is essential to dendrite pruning and morphogenesis. In our mutational analysis, we propose that Frizzled and Arrow are the receptors for Wnt signaling in Drosophila sensory neurons regulating dendritic severing. Additionally, Axin, Wnt repressor, perturbs dendrite pruning in examined cells. After rescuing these neurons with constitutively-active β-catenin, which continuously activates Wnt canonical pathway, we ameliorate pruning phenotypes in neurons resulted from dsh RNAi or Axin overexpression. In conclusion, Wnt canonical pathway is required for dendrite pruning in Drosophila da neurons.