Fig. 1

Non-hepatic endodermal cells are directly converted into hepatoblasts upon Wnt8a overexpression.

(A,B) Wild-type or Tg(hs:wnt8a) embryos were heat-shocked at 26hpf, harvested at 40hpf, and processed for immunostaining with anti-Prox1 (green) and anti-Pdx1 (red) antibodies. Ectopic hepatoblasts were present in the endoderm posterior to the liver-forming region in Wnt8a-overexpressing embryos (B, bracket). (C,D) anti-Prox1 and anti-Pdx1 staining of wild-type embryos at 26hpf and a schematic representation. Prox1 is expressed in endodermal cells at the 1^st to 3^rd somite levels, but not at the 4^th to 6^th somite levels. S1–S6 denotes the 1^st–6^th somite; the pink region indicates the dorsal pancreas (DP). Dashed lines in D outline the Pdx1⁺ region beneath the liver. (E) Cartoons illustrating cell-lineage tracing experiments. (F,G) Wild-type or Tg(hs:wnt8a) embryos were co-injected with sox32 and kikume mRNA into a single cell at the 32-cell stage, resulting in the mosaic expression of Kikume in the endoderm. Endodermal cells at the 5^th somite level were photoconverted at 25.5hpf and then heat-shocked. Excited cells emit red fluorescence (Kik^Red) instead of green (Kik^Green). The embryos were harvested at 40hpf and processed for immunostaining. To reveal the entire endoderm morphology including the dorsal pancreas (dotted lines), both Pdx1 and Kik^green expression, which was detected using the same laser, are shown. Kik^Red+ cells expressed Prox1 (green) in Wnt8a-overexpressing embryos (G, open arrowheads), but not in controls (F, arrowheads). (H–H3) Higher magnification images of the square region in G. (I) Cartoon incorporating all lineage-tracing data. Green and blue lines outline Prox1⁺ and Pdx1⁺ domains, respectively, and n indicates the number of embryos. Dotted lines outline the dorsal pancreas (DP). All confocal images are ventral views with anterior up. Scale bars, 20µm.