Fig. 5. Permissive model for oenocyte specification by abdA. At stage 10, Ato activates rho transcription in C1. Rho may or may not (?) process mSpi to sSpi in the Golgi apparatus at this stage, either way the response in the dorsal ectoderm is blocked (cross). By stage 11, the dorsal ectoderm acquires the full oenocyte prepattern and becomes competent for induction. At this time, Ato is no longer present but AbdA and its co-factor Exd maintain rho transcription, thus keeping sSpi available to activate the EGFR and in turn the hierarchy of oenocyte differentiation genes including: pointed (pnt), argos, spalt (sal), seven up (svp), ventral veins lacking (vvl), Hepatocyte nuclear factor 4 (Hnf4) and delta-aminolevulinate synthase (Alas).