Fig. 5. The posterior limit of endodermal expression of AmphiIslet (A-I), AmphiFoxA2 (J-R), and AmphiHh (S-X) is not affected by altered levels of RA signaling. Anterior to left. Arrowheads indicate the posterior limit of endodermal expression. Scale bars=50 µm. (A-I) AmphiIslet is expressed in the anterior three-quarters of the endoderm in controls at all stages. Expression is not changed by RA or BMS009. (J-R) The posterior limit of AmphiFoxA2 is at the posterior end of the endoderm in DMSO controls and in RA- and BMS009-treated embryos at all stages. (S-X) AmphiHh is expressed strongly in the extreme anterior endoderm and more weakly throughout the remainder of the endoderm in DMSO controls at all stages (S,T). In mid-neurula embryos, the posterior limit of the region of weak endodermal expression is not affected by RA (U) or BMS009 (W). At this stage, AmphiHh expression in the endoderm of RA-treated embryos is largely downregulated (V), while expression in embryos treated with BMS009 appears to be slightly upregulated. A,D,G,J,M,P,S,U,W=20 hours. B,E,H,K,N,Q=24 hours. C,F,I,T,V,X=30 hours. L,O,R=48 hours.