Copper impairs zebrafish swimbladder development by down-regulating Wnt signaling

Copper nanoparticles (CuNPs) are used widely in different fields due to their attractive and effective abilities in inhibiting bacteria and fungi, but little information is available about their biological effects and potential molecular mechanisms on fish development. Here, CuNPs and copper (II) ions (Cu²⁺) were revealed to inhibit the specification and formation of three layers of zebrafish embryonic posterior swimbladder and impair its inflation in a stage-specific manner. CuNPs and Cu²⁺ were also revealed to down-regulate Wnt signaling in embryos. Furthermore, Wnt agonist 6-Bromoindirubin-3'-oxime (BIO) was found to neutralize the inhibiting effects of CuNPs or Cu²⁺ or both on zebrafish swimbladder development. The integrated data here provide the first evidence that both CuNPs and Cu²⁺ act on the specification and growth of the three layers of swimbladder and inhibit its inflation by down-regulating Wnt signaling in a stage-specific manner during embryogenesis.