A model of signaling events regulating zebrafish fin regeneration. A model of signaling events regulating zebrafish fin regeneration. We propose that injury of the tail fin activates as yet unknown signals that result in upregulation of wnt10a and wnt5b. wnt5b expression is also regulated by Wnt/β-catenin signaling activated by wnt10a. Wnt10a activates a β-catenin-dependent signaling pathway that positively regulates fgf20a expression, which has been shown to be required for blastema formation and subsequent regeneration (Whitehead et al., 2005). In addition to its role in regulating fgf20a expression, Wnt/β-catenin signaling might also regulate other genes that are required for blastema formation and proliferation (gray arrow). We propose that wnt5b employs a β-catenin-independent signaling pathway that antagonizes Wnt/β-catenin signaling. However, we cannot exclude the possibility that such β-catenin-independent pathways also inhibit regeneration without impairing Wnt/β-catenin signaling (gray arrow). Arrows do not imply direct events. Cristi L. Stoick-Cooper et al. Development 2007;134:479-489 © 2007.