A cascade of transcription factors expressed in endocrine cell development. Tags that mapped unambiguously to transcription factors and met our count and specificity thresholds were identified and their normalized counts obtained in each of the SAGE libraries that represent the development of the endocrine lineage. (a) A heatmap, generated using the multi-experiment viewer as described in the Materials and methods, of these results is shown. Tags are organized by the order of their expression in the libraries. The libraries shown include: Pdx1 EGFP+ TS17 (P+ TS17); Pdx1 EGFP+ TS19 (P+ TS19); Neurog3 EGFP+ TS20 (N+ TS20); Neurog3 EGFP+ TS21 (N+ TS21); Neurog3 EGFP+ TS22 (N+ TS22); adult isolated islets (Islets). (b) A transcription factor network in β-cell development. The network was generated as described in the materials and methods using Biotapestry to visualize the network . Ins1 and Ins2 are shown as the final products expressed in mature β-cells. Literature reported interactions [8,41] are included with arrow heads indicating positive regulation and perpendicular lines repression. Interactions in pancreatic progenitors (PP), endocrine progenitors (EP) and mature β-cells are shown. (c) The fold enrichment of predicted Foxa2 binding sites, as detected by qPCR, in the promoters of Pdx1, Myt1, Myt3, Neurod1, Nkx2-2, Nkx6-1, and of two sites not predicted to contain a Foxa2 site (NegF1 and NegF2) in ChIP experiments using an anti-Foxa2 antibody compared to IgG. (d) The fold enrichment of predicted Pdx1 binding sites, as detected by qPCR, in the promoters of Foxa2, Ins1, Myt1, Neurod1, Nkx2-2, Nkx6-1, and of two sites not predicted to contain a Pdx1 site (NegP1 and NegP2) in ChIP experiments using an anti-Pdx1 antibody compared to IgG. The data shown are averages of the results obtained from three separate ChIP experiments each with duplicate reactions. Error bars indicate the standard deviation of the averaged replicates.