Fig. 1. Pancreatic anatomy, lineages and genes. (A) The dorsal and ventral pancreata (dp and vp, respectively) arise at approximately E8.5 in the mouse (top), from two strips of gut endoderm (marked dp, vp) that are located adjacent to the forming liver (li) within the developing gut endoderm. At E10.5 (middle), the pancreatic primordia bud out into the surrounding mesenchyme and occupy a position between the stomach (st) and intestine (in). Subsequent gut rotation, from E12.5 onward (bottom), brings the two lobes into closer apposition, although each maintains its original ductal connection to the intestine and/or common bile duct (cbd). (B) Lineage tracing indicates that all mature pancreatic cell types derive from progenitors that express Pdx1 and/or Ptf1a (purple), and that a subset of these progenitors go on to express Ngn3 and differentiate into islet cells. Genes listed in red are required for various aspects of the indicated steps, as described in the text.