Fig. 1. Scheme of the temporal and spatial gene expression analysis for four stages of islet development. The red box highlights the temporal gene expression comparison and the green boxes highlight the spatial expression comparisons. (1) At E7.5, endoderm (black arrowhead) and mesectoderm (red arrowhead) were manually separated and analyzed. (2) At E10.5, the eGFP⁺ cells from pancreatic buds (red dashed lines), stomach/duodenum (white dashed lines; two solid white lines indicate the approximate borders of dissection), and eGFP^– cells from Pdx1-eGFP transgenic animals were separated by FACS and analyzed. (3) At E13.5, endocrine progenitor cells expressing Ngn3-eGFP were separated by FACS from eGFP^– cells (yellow arrowhead, primarily exocrine and ductal cells) and both eGFP⁺ and eGFP^– cells were analyzed. Adult islets were hand picked and used for direct analysis (green dashed lines. The blue staining within the islet is from Pdx1-lacZ). cRNA probes for each sample were hybridized to Affymetrix microarrays Mu11K, Mu74Av1 or Mu74Av2 (Materials and methods). Temporal analysis (the red box) compared the gene expression patterns of endoderm, pancreatic progenitors (Pdx1-eGFP⁺), endocrine precursors (Ngn3-eGFP⁺), and adult islets. Spatial analysis (green boxes 1, 2 and 3) compared different samples from the same stages, e.g. genes expressed in E7.5 endoderm versus mesoderm + ectoderm.