Patterns of temporal utilization of site-specific transcription factors. (a) Binary representation of TF expression according to the BDGP in situ database: black, expressed; white, not expressed. Expression behavior can be roughly categorized into six classes, no embryonic expression, diverse expression, early TFs, late TFs, those with continuous zygotic expression and continuous expression (including maternal contribution). The four largest classes are detailed in the main text. (b) Temporal utilization for different TF families. Absolute numbers of expressed TFs are provided underneath each panel. Note that roughly half of the TFs per family have been covered by the BDGP. HTH: helix-turn-helix.