Figure 2

Dkk1 Controls Organization of Filamentous Actin

(A) Single-plane confocal images of the axis in Tg(gsc:GFP) embryos (green axis) labeled with phalloidin (red) at the tail bud (TB) stage show disruption of filamentous actin organization in Dkk1-expressing embryos (n = 12). Expansion of axial cell fate induced by knock down (KD) of the nodal antagonists Lefty1 and Lefty2 (n = 6) or upregulation of Wnt target gene transcription by Tcf3 KD (n = 7) has no effect on axial polarity. Conversely, the loss of Dkk1 (n = 5) results in a compact hyperpolarized axis. Scale bar, 20 μm.

(B) The loss of filamentous actin boundary organization induced by Dkk1 is not dependent on planar cell polarity (PCP) signaling. Single-plane confocal images of Tg(gsc:GFP) embryos (green axis) labeled with phalloidin (red) at the late tail bud (LB) stage show a distinct convergence extension phenotype in Vangl2 knock down (Vangl KD) embryos (n = 8) compared to control embryos (n = 11), distinct from the Dkk1-induced phenotype (n = 9). Vangl KD embryos injected with low levels of Dkk1 RNA display an additive phenotype (n = 11). Scale bar, 20 μm.

(C) Axial boundary straightness was quantified in phalloidin-labeled Tg(gsc:GFP) embryos at the late tail bud (LB) stage. Downregulation of Vangl2 (n = 16 boundaries) results in a straighter axial boundary than control (n = 22 boundaries). Reduction of boundary straightness in Dkk1-RNA-injected embryos (n = 18 boundaries) is not rescued by downregulation of Vangl2 (n = 16 boundaries). p > 0.05, ns, not significant, ^∗p < 0.05, ^∗∗∗p < 0.001. Scale bar: 20 μm.