Figure 1. Specification and development of SG cell types.

(A) Gene network involved in specifying SGs to form in the ventral domains of PS2 and in the activation and maintenance of key TFs and signaling pathways involved in cell fate choices within the SG and in maintaining those cell fates. Green indicates factors involved in positive regulation of SGs and genes expressed in secretory cells. Red indicates factors involved in negative regulation of SGs or expressed in salivary duct cells. Notch (yellow) signaling is required to specify imaginal ring cells. (B) Secretory, duct and imaginal ring cells of the SG arise from different dorsal ventral positions within the primordia. The more dorsal cells form the secretory tubes (green cells). The most ventral cells form the salivary duct (red cells). The cells in between become the imaginal ring (yellow cells).