Wnt Signaling In Embryos Research Articles

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.

HMGB factors are required for posterior digit development through integrating signaling pathway activities

The chromatin factors Hmgb1 and Hmgb2 have critical roles in cellular processes, including transcription and DNA modification. To identify the function of Hmgb genes in embryonic development, we generated double mutants of Hmgb1;Hmgb2 in mice. While double null embryos arrest at E9.5, Hmgb1(-/-) ; Hmgb2(+/-) embryos exhibit a loss of digit5, the most posterior digit, in the forelimb. We show that Hmgb1(-/-) ; Hmgb2(+/-) forelimbs have a reduced level of Shh signaling, as well as a clear downregulation of Wnt and BMP target genes in the posterior region. Moreover, we demonstrate that hmgb1 and hmgb2 in zebrafish embryos enhance Wnt signaling in a variety of tissues, and that double knockdown embryos have reduced Wnt signaling and shh expression in pectoral fin buds. Our data show that Hmgb1 and Hmgb2 function redundantly to enhance Wnt signaling in embryos, and further suggest that integrating Wnt, Shh, and BMP signaling regulates the development of digit5 in forelimbs.

Wnt signaling and the evolution of pattern formation

Evolution of gastrulation was crucial for metazoan diversification, but the molecular origins of developmental polarity that led to the onset of gastrulation mechanisms are unknown. Nuclear ß‐catenin marks the site of gastrulation in cnidarians and several bilaterians, raising the possibility that evolution of mechanisms to asymmetrically activate Wnt signaling in embryos may have been causal in evolution of gastrulation. We have shown that localized activation of Dishevelled (Dsh), a key regulator of Wnt/ß ‐catenin signaling, plays a crucial role in germ layer segregation and gastrulation in sea urchins and in the cnidarian Nematostella vectensis. Dsh also regulates the Wnt/Planar Cell Polarity (PCP) pathway, which mediates vertebrate gastrulation movements. In Nematostella, blocking Dsh signaling in the PCP pathway, or blocking Strabismus function using morpholinos blocks gastrulation, suggesting that Wnt/PCP signaling mediated gastrulation movements in the last common ancestor to cnidarians and bilaterians. Because Dsh can regulate multiple Wnt pathways, it may have been a critical link between evolution of cell fate specification and evolution of gastrulation morphogenesis. Our results also support the hypothesis that one ancient function of PCP signaling was to mediate the developmental asymmetry that led to the evolution of gastrulation. (Supported by NSF grants IOS 0720365 and IOS 0754323)

The Tumor Suppressor PRDM5 Regulates Wnt Signaling at Early Stages of Zebrafish Development

PRDM genes are a family of transcriptional regulators that modulate cellular processes such as differentiation, cell growth and apoptosis. Some family members are involved in tissue or organ maturation, and are differentially expressed in specific phases of embryonic development. PRDM5 is a recently identified family member that functions as a transcriptional repressor and behaves as a putative tumor suppressor in different types of cancer. Using gene expression profiling, we found that transcriptional targets of PRDM5 in human U2OS cells include critical genes involved in developmental processes, and specifically in regulating wnt signaling. We therefore assessed PRDM5 function in vivo by performing loss-of-function and gain-of-function experiments in zebrafish embryos. Depletion of prdm5 resulted in impairment of morphogenetic movements during gastrulation and increased the occurrence of the masterblind phenotype in axin+/− embryos, characterized by the loss of eyes and telencephalon. Overexpression of PRDM5 mRNA had opposite effects on the development of anterior neural structures, and resulted in embryos with a shorter body axis due to posterior truncation, a bigger head and abnormal somites. In situ hybridization experiments aimed at analyzing the integrity of wnt pathways during gastrulation at the level of the prechordal plate revealed inhibition of non canonical PCP wnt signaling in embryos overexpressing PRDM5, and over-activation of wnt/β-catenin signaling in embryos lacking Prdm5. Our data demonstrate that PRDM5 regulates the expression of components of both canonical and non canonical wnt pathways and negatively modulates wnt signaling in vivo.