Figure 6

Figure 6

Ubiquitous Expression of GFP-Tagged Dkk1 Reveals Polarized Distribution of Dkk1 Protein at Tissue and Subcellular Levels

(A) Live Tg(hsp70l:dkk1b-GFP) embryos expressing Dkk1 (green) at different epiboly (EB) stages. On the right panel, higher magnification single-plane confocal image, of the area highlighted by the dashed frame, shows exclusion of Dkk1GFP from the axis, despite abundant extracellular Dkk1GFP in the surrounding non-axial tissue. The extracellular non-bound pool of Dkk1GFP is not detectable after fixation. See also Figure S2. Scale bar, 20 μm.

(B) Subcellular localization of Dkk1GFP in 80% epiboly (EB) and tail bud (TB) stage fixed embryos. Single-plane high magnification confocal images are shown of the region of interest in dashed white frames. Localization of Dkk1GFP to actin-rich membrane junctions was visualized by coexpression with red fluorescent protein-tagged actin-binding utrophin (RFP-UTR, red). Arrow highlights Dkk1GFP and RFP-UTR colocalization at a cell-cell junction. n = 6 for each condition. Scale bar, 20 μm.

(C) Dkk1GFP colocalizes with plasma membrane-associated β-catenin (red)-positive puncta. Embryos were fixed shortly after heat shock. Arrowheads highlight β-catenin positive puncta (red), which colocalize with Dkk1GFP (arrows).

(C’) Quantification of colocalization (n = 10). Mean Pearson’s R value is 0.60 for Dkk1-β-catenin and 0.03 for the randomized control. Scale bar, 20 μm.