Wnt'er in liver: Expression of Wnt and frizzled genes in mouse

The Writ signaling pathway is essential for a wide array of developmental and physiological processes. Writs are extracellular ligands that hind to frizzled (Fz) receptors at the membrane, canonically inducing beta-catenin nuclear translocation and activation. Although beta-catenin has been shown to be critical in liver biology, the expression of the 19 Wnt and 10 Fz genes in liver remains undetermined. We report comprehensive analysis of Wnt and Fz expression in whole liver as well as individual cell types: freshly isolated and plated hepatocytes, biliary epithelial cells, normal and activated stellate and Kupffer cells, and sinusoidal endothelial cells (SECs). Oligonucleotides for the 19 Writ, 10 frizzled receptors genes, and secreted Frizzled-related protein-1 (sFRP or Fzb) were synthesized based on the available sequences. A total of 11 Writs and 8 Fz genes and Fzb were expressed in normal liver. Although only 6 Wnt and 5 Fz genes were expressed in freshly isolated hepatocytes, 8 Writ genes, 7 Fz genes, and Fzb were expressed in plated hepatocytes. Although 12 Writ and 7 Fz genes were expressed in biliary tree, additional Fz9 and Fzb were only expressed in cultured biliary epithelial cells. The same 14 Wnt and 7 Fz genes were expressed in both activated and normal stellate and Kupffer cells; only Fzb was expressed in their activated state. Also, 11 Writ, seven Fz, and Fzb genes were expressed in SECs. Conclusion: These data indicate that most Wnt and frizzled genes are expressed in the liver and might be playing important roles in liver pathobiology via canonical and noncanonical pathways.