Fig. 5

Histone deacetylase function is required during late somitogenesis for liver specification and differentiation. TSA was applied at various time points, and digestive tract morphogenesis, liver specification and differentiation were examined by foxA1, hhex, prt/wnt2bb, and cp expression, respectively. 600 nM TSA produced the closest phenocopy of the hdac1^s436 phenotype when assessed by foxA1 expression (compare panel B and C). This concentration was used in subsequent experiments. Horizontal bars show an expansion of the digestive tract in both TSA treated and hdac1 mutants when compared to wild type embryos (compare panels B, C with A). (D–I) Hepatoblast specification in TSA treated embryos was assessed by hhex expression. Application of TSA at 14 hpf resulted in an absence of hepatic hhex expression at both 24 and 48 hpf (E, H). However, treatment at 18 hpf resulted in wild type expression of hepatic hhex at 24 hpf (bracket, F), although strongly reduced at 48 hpf (arrowhead, I). (J–L) prt/wnt2bb expression was assessed in TSA treated embryos. TSA treatment at 16 hpf resulted in an absence of prt/wnt2bb expression in the LPM abutting the organ-forming endoderm (K), however application of TSA at 18 hpf resulted in wild type-like expression of prt/wnt2bb (bracket, L). (M–O) Hepatocyte differentiation in TSA treated embryos was assessed by cp expression. Embryos treated with TSA at 14 hpf showed no cp expression at 48 hpf (N), however embryos treated at 18 hpf express cp, but in a reduced domain (arrow, O). DMSO was added as a control in all cases (A, D, G, J, M), asterisk indicates position of the pancreas. Anterior to the top.