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To better understand the relationship between the endocrine and exocrine cell types in the Xenopus pancreas, we have cloned the Xenopus amylase cDNA and compared its expression profile with that of four other pancreatic markers: insulin, glucagon, elastase and trypsinogen. Our results demonstrate that the first pancreatic marker to be expressed is insulin, exclusively in the dorsal pancreas. These insulin-expressing cells form small groups which resemble islets, but no insulin is detected in the ventralpancreas until stage 47. In contrast, the exocrine markers, amylase, elastase and trypsinogen are first expressed only in the ventralpancreas beginning at stage 41; by stage 45 their expression extends into the dorsal pancreas. Glucagon, on the other hand, is not expressed in the pancreas until stage 45. In the endocrine cell clusters we do not find glucagon-expressing cells surrounding insulin-expressing cells, either in the tadpole or in the mature frog pancreas.
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11960704
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Fig. 2. Exocrine gene expression in isolated whole guts. (A–C) Amylase expression. Expression of amylase is first detected in the ventralpancreas at stage 41. By stage 45, however, expression has spread throughout both the dorsal and ventralpancreas. (D–F) Elastase expression. As seen with amylase, elastase is first detected in the ventralpancreas and thereafter throughout the whole pancreas. (G–I) Trypsinogen expression. The time course of trypsinogen expression is identical to amylase. (A,D,G) Stages 40–41. (B,E,H) Stages 42–44. (C,F,I) Stages 45–46.
Fig. 3. Endocrine gene expression in isolated whole guts (A–D) Insulin expression. Initially expression is only seen in the dorsal (d) pancreas at stage 41. At stage 45 insulin expression is detected in several large groups of cells in the dorsal pancreas. By stage 47 expression is also seen in the ventral (v) pancreas. (E–H) Glucagon expression. Glucagon-expressing cells are first detected at stage 41 in the stomach. No expression is seen in the pancreas until stage 45, and by stage 47 large numbers of glucagon-expressing cells are present throughout the whole pancreas as well as the stomach and the intestine. Labels in figures are d for dorsal pancreas and v for ventralpancreas. (A,E) Stages 40–41. (B,F) Stages 42–44. (C,G) Stages 45–46. (D,H) Stages 47–48.
Fig. 4. Comparison of insulin and glucagon expression in the pre- and post-metamorphic pancreases. (A,D,E,F) Insulin expression (B,C) Glucagon expression. At late stages, insulin is expressed throughout the whole pancreas in much larger groups of cells in the dorsal pancreas than in the ventralpancreas. (B) Insulin in red and glucagon in blue. Glucagon and insulin-expressing cells form discrete groups of cells that do not overlap. No islets are seen with glucagon cells surrounding insulin cells. (C) Section through a stage 47 pancreas showing glucagon expression in small groups on the periphery of the pancreas. (D–F) Serial sections through a late pancreas, around stage 47. Every other section is shown and therefore each section is 15 μm apart. Note the discrete groups of insulin cells on the periphery and the lighter internal staining cells (arrowhead). Also note the hollow center in the insulin groups (F, arrow). (G–I) Double in situ hybridization for insulin (magenta) and glucagon (blue). (G) Stage 54 tadpolepancreas. (H,I) Froglet pancreas. As seen in earlier stages, glucagon-expressing cells do not surround the insulin-expressing cells (arrows). Glucagon-expressing cells are found exclusively at the periphery of the pancreas, while insulin-expressing cells form large interconnected groups throughout the whole pancreas. H and I are sections from the same froglet pancreas 42 μm apart.
