Fig. 4

Decrease in Bmp Signaling Leads to a Decrease in Liver Tissue and Increase in pdx1 Expressing Cells

(A–D) Dorsal views of hhex (A and B) and pdx1 (C and D) expression, comparing wild-type (A and C) and alk8 mutants (B and D) at 28 hpf. hhex is expressed in the liver (black arrow) as well as the dorsal pancreatic bud (white arrow) (A). hhex expression is greatly reduced in the liver forming region (black arrow) of alk8 mutants but appears unaffected in the dorsal pancreatic bud (white arrow) (B). pdx1 expression is expanded in alk8 mutants (D) compared to wild-type (C).

(E–F′) Confocal projections of Tg(gutGFP)^s854 wild-type (E and E′) and alk8 mutants (F and F′) at 28 hpf, stained for Pdx1 (red, outlined by yellow dashed line in E′ and F′) and Prox1 (white). The dorsal pancreatic bud (arrows; outlined by white dashed line) is also Pdx1 positive. Compared to wild-type (E and E′), in alk8 mutants (F and F′), the Pdx1 expression domain has expanded into the Prox1 expression domain, which is itself reduced.

(G and H) Dorsal views of pdx1 expression, comparing wild-type (G) and alk8 mutants (H) at 18 hpf. pdx1 is expressed at high levels in the most medial cells (asterisks) and at low levels in lateral cells (arrows) (G). In alk8 mutants (H), low levels of pdx1 expression were expanded laterally (the percentage of alk8 mutants showing a substantial lateral expansion of pdx1 expression was 54%, n = 7/13).

(I and J) Dorsal views of hhex expression comparing wild-type (I) and bmp2b MO-injected alk8 heterozygous (J) embryos at 28 hpf. Compared to wild-type (I), hhex expression was greatly reduced in the liver-forming region (black arrows) of most (n = 16/23) alk8 heterozygous embryos injected with bmp2b MO (J). hhex expression in the dorsal pancreatic bud (white arrows) appears unaffected.