Tissue specificity of site-specific transcription factors. (a) Proportion of ubiquitously expressed genes along the developmental time axis, separated into TFs and non-TFs. The expression patterns of TFs and non-TFs are significantly different between stages 4 and 12 (P < 10-4), with less ubiquitous and more restricted expression patterns for the TFs. (b) Adult specificity. Gene expression clusters with adult tissue-specificity were queried for their specificity in late embryonic development (BDGP dataset stages 13 to 16). Shown is the expression breadth as the number of anatomical structures used in the annotation, as well as the percentage of genes with frequently encountered annotations. For example, for the 40 TFs primarily expressed in adult head, crop and gut, there is embryonic expression information for 23 of them. These genes are most frequently annotated for expression in the midgut (35%) and dorsal epidermis (35%). Interestingly, very frequently, adult tissue-specific TFs are involved in embryonic nervous system development. CNS: central nervous system; SNS: stomatogastric nervous system; VNC: ventral nerve cord.