Wnt Signaling Is Required for Early Development of Zebrafish Swimbladder

Ao Yin,Svitlana Korzh,Cecilia L Winata,Vladimir Korzh,Zhiyuan Gong,Hector Escriva

doi:10.1371/journal.pone.0018431

Ao Yin, Svitlana Korzh + Show 4 more

Open Access

https://doi.org/10.1371/journal.pone.0018431

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Abstract

BackgroundWnt signaling plays critical roles in mammalian lung development. However, Wnt signaling in the development of the zebrafish swimbladder, which is considered as a counterpart of mammalian lungs, have not been explored. To investigate the potential conservation of signaling events in early development of the lung and swimbladder, we wish to address the question whether Wnt signaling plays a role in swimbladder development.Methodology/Principal FindingsFor analysis of zebrafish swimbladder development, we first identified, by whole-mount in situ hybridization (WISH), has2 as a mesenchymal marker, sox2 as the earliest epithelial marker, as well as hprt1l and elovl1a as the earliest mesothelial markers. We also demonstrated that genes encoding Wnt signaling members Wnt5b, Fz2, Fz7b, Lef1, Tcf3 were expressed in different layers of swimbladder. Then we utilized the heat-shock inducible transgenic lines hs:Dkk1-GFP and hs:ΔTcf-GFP to temporarily block canonical Wnt signaling. Inhibition of canonical Wnt signaling at various time points disturbed precursor cells specification, organization, anterioposterior patterning, and smooth muscle differentiation in all three tissue layers of swimbladder. These observations were also confirmed by using a chemical inhibitor (IWR-1) of Wnt signaling. In addition, we found that Hedgehog (Hh) signaling was activated by canonical Wnt signaling and imposed a negative feedback on the latter.Significance/ConclusionWe first provided a new set of gene markers for the three tissue layers of swimbladder in zebrafish and demonstrated the expression of several key genes of Wnt signaling pathway in developing swimbladder. Our functional analysis data indicated that Wnt/β-catenin signaling is required for swimbladder early development and we also provided evidence for the crosstalk between Wnt and Hh signaling in early swimbladder development.

Highlights

The common evolutionary origin of the teleost swimbladder and tetrapod lung has been long recognized, but the vast anatomical and functional differences between the two organs weaken the common origin assumption [1]
We first identified a new set of molecular markers for all the three tissue layers of zebrafish swimbladder, with sox2 as the earliest epithelial marker, hprt1l and elovl1a as the earliest mesothelium markers, and has2 as a new mesenchyme marker
By using the two heat-shock inducible Wnt inhibition transgenic zebrafish lines, hs:Dkk1-GFP and hs:DTcf-GFP, we demonstrated that the expression of GFPtagged Dkk1/Tcf was induced in the swimbladder

Summary

Introduction

The common evolutionary origin of the teleost swimbladder and tetrapod lung has been long recognized, but the vast anatomical and functional differences between the two organs weaken the common origin assumption [1]. Wnt signaling pathway has been reported to play critical roles in mammalian lung development [5]. Studies have shown that Wnt signaling only plays roles in late lung development by regulating lung epithelium and mesenchyme proliferation. Whereas loss of b-catenin or overexpression of Wnt inhibitor dkk in lung epithelium after lung specification inhibits distal airway epithelial development and a global proximalization [6], mesenchymespecific inhibition of b-catenin results in reduced mesenchymal proliferation [7,8]. It has been shown that Wnt signaling is required for lung endoderm specification and progenitor fate determination [15]. Wnt signaling plays critical roles in mammalian lung development. Wnt signaling in the development of the zebrafish swimbladder, which is considered as a counterpart of mammalian lungs, have not been explored.

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