PI3K-FOXO信号调控涡虫干细胞自我更新和分化命运决定的机制研究

Blastema formation is critical to planarian regeneration and depends on the precise coordination of self-renewal and differentiation of somatic stem cells in planarian. During blastema formation, the stem cells in anterior blastema undergo differentiation into blastema cells, however, the stem cells in post-blastema region maintain the stem cell pool via self-renewal. What signals and mechanisms determine the difference in cell fate between stem cells in different locations? ERK signaling allows planarian stem cells to simultaneously exit from the self-renewal state and enter the differentiation state, but it remains ambiguous when, where, and how the signal is activated. In our previous study, we found that both of pi3k and foxO genes were indispensable for the blastema formation, but the expression distribution was different: pi3k was specifically expressed in the post-blastema region and inhibited ERK activation; while foxO expression showed the aggregated distribution in the anterior blastema, and promotes ERK activation. Therefore, we hypothesized that the pi3k and foxO genes may determine the fate of the planarian stem cells via the position-specific activation of ERK signaling, and synergistically contribute to blastema formation. In this proposal, we will employ in vivo model of the planarian regeneration and in vitro cell model to study the expression patterns, regulatory functions and molecular mechanisms of pi3k and foxO genes, in order to reveal the role and mechanism of PI3K-FOXO signaling in determining the fate of stem cells during blastema formation in planarian.

芽基是涡虫再生的关键，芽基形成依赖于涡虫干细胞自我更新和分化的精密协调：芽基前端的干细胞经历分化成为芽基细胞，芽基后区的干细胞通过自我更新维持干细胞储量。是什么信号和机制决定了干细胞在不同位置的命运差异？ERK信号可驱使干细胞退出自我更新状态并向芽基细胞分化，但该信号何时、何处、如何被激活尚未完全清楚。申请人前期研究发现：pi3k和foxO基因表达对涡虫芽基的形成不可或缺，但分布不同：pi3k在芽基后区表达，抑制ERK信号激活；foxO聚集于芽基前端表达，促进ERK信号激活。因此，本项目提出pi3k和foxO基因可能通过位置特异性地激活ERK信号来决定涡虫干细胞的命运，协同调节涡虫芽基形成。本项目拟采用涡虫再生模型和体外细胞模型，研究pi3k和foxO基因表达模式、调控功能和分子机制，以期揭示PI3K-FOXO信号在涡虫芽基形成过程中对干细胞命运决定的作用机制，为阐明涡虫再生机理提供参考。

涡虫具有强大的再生能力和丰富的成体干细胞，是研究动物再生和干细胞调控机制的理想模型。涡虫的再生依赖于成体干细胞自我更新和分化的精密协调，但该过程受何种信号和机制调控尚未阐明。本项目聚焦PI3K和FOXO信号对涡虫再生及干细胞命运决定的调控机制，重点开展了以下研究：(1)克隆并鉴定东亚三角涡虫PI3K和FOXO同源基因，探明其在涡虫再生过程中的时空表达模式；(2)利用小分子化合物和RNAi技术干预PI3K或FOXO信号通路，明确Djpi3k和DjfoxO基因参与调控涡虫再生及内稳态维持；(3)阐明PI3K信号通过调节干细胞自我更新和细胞凋亡反应调控涡虫再生的机制；(4)基于RNA-seq分析FOXO调控涡虫再生靶点，并阐明FOXO信号通过调节涡虫干细胞分化行为调控涡虫再生，且该进程与ERK信号的激活关系密切。上述研究结果进一步提示：PI3K和FOXO信号在涡虫组织再生和内稳态维持中发挥重要作用，Djpi3k和DjfoxO基因分别通过调节自我更新和分化行为决定涡虫干细胞命运，进而协调再生芽基形成及细胞谱系特化，有望为组织修复与再生提供干预靶点。