Distribution of TFs as a function of their expression profiles. The colored regions of the pie chart highlight the TFs categorized as consistently expressed in a single organ system (red), temporally restricted early or late in embryonic development to a single organ system (shades of green), or expressed in multiple organ systems (blue). The segments of the pie chart shaded in grey from light to dark are: not expressed (25 TFs), maternally expressed only (34 TFs) and ubiquitously expressed only (114 TFs), respectively. TFs restricted to a single organ system both early and late are listed on the left with the associated organ system. The time line on the right shows the division of early and late development with diagram illustrating development of organ systems at stages 5 (early body plan determination and organ specification), 9 (organ specification nearly complete), and 16 (organ system differentiation).