Fig. 4

Activity of pancreatic ptf1a enhancers relative to the intact locus. Activity of the early +1ptf1a (B, D, G) and the autoregulatory (E, H) enhancers was assayed in transgenic embryos by in situ hybridization for egfp. For comparison, egfp expression is also shown for the intact locus in ptf1a:egfp^jh1 transgenic embryos (A, C, F). At 30 hpf, none of the embryos had detectable expression in pancreatic precursors (data not shown). At 34 hpf (A, B) and 38 hpf (C–E), all ptf1a:EGFP^jh1 embryos (n=24 and 40) showed a group of positive cells stretched across the midline from left anterior to right posterior (A, C), a subset of embryos transgenic for the early enhancer showed smaller groups of positive cells, in the left anterior endoderm (B, D), while all embryos transgenic for the autoregulatory enhancer lacked expression, shown at 38 hpf (E). At 42 hpf, ptf1a:egfp^jh1 embryos had larger, less scattered groups of positive cells (F), while both the early enhancer (G) and the autoregulatory enhancer (H) were active in a subset of cells in the same domain. For all photographs, yolk was dissected away and the endoderm is shown from the ventral side; embryos are oriented with anterior to the left and left to the top.