Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
Development. 2012 Feb;139(3):514-24. doi: 10.1242/dev.071746. Epub 2011 Dec 21.
Cilia are essential for normal development. The composition and assembly of cilia has been well characterized, but the signaling and transcriptional pathways that govern ciliogenesis remain poorly studied. Here, we report that Wnt/β-catenin signaling directly regulates ciliogenic transcription factor foxj1a expression and ciliogenesis in zebrafish Kupffer's vesicle (KV). We show that Wnt signaling acts temporally and KV cell-autonomously to control left-right (LR) axis determination and ciliogenesis. Specifically, reduction of Wnt signaling leads to a disruption of LR patterning, shorter and fewer cilia, a loss of cilia motility and a downregulation of foxj1a expression. However, these phenotypes can be rescued by KV-targeted overexpression of foxj1a. In comparison to the FGF pathway that has been previously implicated in the control of ciliogenesis, our epistatic studies suggest a more downstream function of Wnt signaling in the regulation of foxj1a expression and ciliogenesis in KV. Importantly, enhancer analysis reveals that KV-specific expression of foxj1a requires the presence of putative Lef1/Tcf binding sites, indicating that Wnt signaling activates foxj1a transcription directly. We also find that impaired Wnt signaling leads to kidney cysts and otolith disorganization, which can be attributed to a loss of foxj1 expression and disrupted ciliogenesis in the developing pronephric ducts and otic vesicles. Together, our data reveal a novel role of Wnt/β-catenin signaling upstream of ciliogenesis, which might be a general developmental mechanism beyond KV. Moreover, our results also prompt a hypothesis that certain developmental effects of the Wnt/β-catenin pathway are due to the activation of Foxj1 and cilia formation.
纤毛对于正常发育是必需的。纤毛的组成和组装已经得到很好的描述，但是调控纤毛发生的信号和转录途径仍然研究得很少。在这里，我们报告 Wnt/β-连环蛋白信号直接调控斑马鱼 Kupffer 囊（KV）中的纤毛发生转录因子 foxj1a 的表达和纤毛发生。我们表明 Wnt 信号在时间上和 KV 细胞自主地作用以控制左右（LR）轴的确定和纤毛发生。具体而言，减少 Wnt 信号导致 LR 模式的破坏、纤毛变短和变少、纤毛运动丧失以及 foxj1a 表达下调。然而，这些表型可以通过 KV 靶向过表达 foxj1a 来挽救。与先前被认为参与调控纤毛发生的 FGF 途径相比，我们的上位研究表明 Wnt 信号在调控 KV 中 foxj1a 表达和纤毛发生方面具有更下游的功能。重要的是，增强子分析表明，foxj1a 的 KV 特异性表达需要存在推定的 Lef1/Tcf 结合位点，表明 Wnt 信号直接激活 foxj1a 转录。我们还发现，受损的 Wnt 信号导致肾脏囊肿和耳石组织紊乱，这可归因于 foxj1 表达的丧失以及在发育中的肾前导管和耳石囊中纤毛发生的破坏。总之，我们的数据揭示了 Wnt/β-连环蛋白信号在纤毛发生之前的一个新作用，这可能是 KV 之外的一种普遍发育机制。此外，我们的结果还提示了一个假设，即 Wnt/β-连环蛋白途径的某些发育效应是由于 Foxj1 的激活和纤毛形成。
