Wnt/β-catenin signaling directly regulates Foxj1 expression and ciliogenesis in zebrafish Kupffer’s vesicle

Abstract

SUMMARYCilia 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/-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/-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/-catenin pathway are due to the activation of Foxj1 and cilia formation. KEY WORDS: Wnt/-catenin signaling, Ciliogenesis, Foxj1, Kupffer's vesicle ZebrafishWnt/-catenin signaling directly regulates Foxj1 expression and ciliogenesis in zebrafish Kupffer's vesicle

ERK7 regulates ciliogenesis by phosphorylating the actin regulator CapZIP in cooperation with Dishevelled

“…Because Wnt signalling is known to be important for head formation 38 , there may be a link between ERK7 and Wnt signalling. Interestingly, FoxJ1 expression has been shown to be regulated by canonical Wnt signalling 39,40 . Thus, a canonical Wnt signalling pathway may regulate ERK7 expression levels through FoxJ1.…”

Context-Dependent Regulation of Wnt Signaling through the Primary Cilium

“…A theme that has gained recent attention is the notion that Wnt signaling may be upstream of ciliogenesis and that components of the canonical Wnt pathway regulate cilia formation. [54][55][56] Although some Wnt signal transducing proteins may govern the expression of genes essential for cilia formation and possibly the polarity of cilia, it is still unclear why Wnt3a is required for left-right asymmetry but not normal ciliogenesis at the node. 56 To shed some light on this issue and perhaps to address an ongoing debate whether there is a functional link between Wnt signaling and the cilium, contextspecific regulation is perhaps most prevalent when thinking about the conflicting data published to date.…”

Laminin β1a controls distinct steps during the establishment of digestive organ laterality

“…Activation of Wnt/β-catenin signaling results in loss of cardiac asymmetry, and affects morphology of the KV, with larger KV and increased cilia number. By contrast, reduction of Wnt3 or Wnt8 results in shorter cilia and randomization of spaw expression, with effects on both heart and digestive organs sidedness (Nakaya et al, 2005;Lin and Xu, 2009;Caron et al, 2012). In addition, the Rho kinase Rock2b controls anterior-posterior asymmetric placement of ciliated cells in the KV, and subsequently L-R patterning of the embryo (Wang et al, 2011).…”