Identification of the dorsal pancreas progenitors.

<p><b>A–B.</b>A cartoon depicting a 9–11 SS embryo labeled over the third somite and slightly lateral on the right side (A) and a bright field/fluorescence merged image of the actual 9 SS embryo revealing the DiI (red) labeled cells (B). <b>C.</b> After culture, the merged image reveals that the resultant 25 SS embryo contained DiI labeled descendants in the dorsal gut (lower red) as well as a smaller patch of visible descendants in the ventral/lateral gut tube (upper red). <b>D–E.</b> Transverse sections as indicated by the dashed lines in (C) revealed the co-localization of DiI (red) in the PDX1-positive (green) dorsal pancreas bud (dp, E) but not in the ventral pancreas bud (vp, D). <b>F–H.</b> A cartoon representing a 5 SS embryo labeled over the third somite pair, as indicated in the cartoon (F) and shown in the actual labeled 5 SS embryo (G) that was cultured to the 20 SS (H). <b>I.</b> Section analysis of the embryo indicated in (H) with PDX1 (green) reveals DiI labeled descendants throughout the dorsal pancreas (arrowheads in I’, boxed region in I is magnified in I’). <b>J.</b> A cartoon of a 5 SS embryo labeled over the left first and second somite, cultured through the 20 SS and processed as above. <b>K–M.</b> Transverse sections through this embryo are aligned in a rostral to caudal manner as indicated by the arrow. DiI labeled descendants (red) are found in the dorsal endoderm rostral to the dorsal pancreas (K) and only slightly overlap with the rostral-most portion of the PDX1-positive dorsal pancreas bud (arrowhead in L). All of the more caudal sections of the dorsal pancreas (green) do not contain DiI labeled cells (M). <b>N.</b> A cartoon depicting a 5 SS embryo labeled in the endoderm over the caudal most fourth and much of the fifth somite. <b>O–Q.</b> Section analysis of the resultant 23 SS embryo, arranged in a rostral to caudal manner as indicated by the arrow, revealed that DiI labeled cells were absent from the rostral regions of the dorsal pancreas bud (green, O) but overlapped slightly with the caudal portion of the dorsal bud (arrowhead, P) and extend into gut tube caudal to the dorsal pancreas bud (red cells in Q). In all sections the arrowheads indicate region of DiI overlap with the dorsal pancreas bud.