Retinoic Acid-Activated Ndrg1a Represses Wnt/β-catenin Signaling to Allow Xenopus Pancreas, Oesophagus, Stomach, and Duodenum Specification
Figure 2
RA directly activates ndrg1a expression in Xenopus archenteron roof endoderm cells.
(A–O) RA signaling is necessary and sufficient to activate ndrg1a expression in the archenteron roof endoderm cells as well as in the pancreas, oesophagus, stomach, and duodenum primordia. Embryos were treated with 0.25 µM BMS453 or 5 µM RA at stage 10 for one hour, collected at stages indicated in the control panels, and subjected to whole mount in situ hybridization analyses of ndrg1a expression. (A–I) Whole mount in situ hybridization on bisected embryos, anterior toward the left. (J–O) Lateral view, head toward the left. Red arrows in panels K and N and red triangles in panels L and O point to the loss or expansion of ndrg1a expression in pancreas, oesophagus, stomach, and duodenum upon BMS453 or RA treatment, respectively. (P–S) RA directly activates ndrg1a expression in Xenopus archenteron roof endoderm cells. Embryos were treated with cycloheximide (CHX, 10 µg/ml), 5µM RA, or both at stage 15 for one hour, fixed at stage 20, and bisected for whole mount in situ hybridization analyses of ndrg1a expression. For the combined treatment, CHX was added 15 min before the application of RA. Anterior is toward the left. The numbers of embryos showing the illustrated phenotypes are given in the corresponding images.