The distinction between the dorsal and ventral wing surfaces is a critical one in insect development. This is especially true in the case of butterflies, where the dorsal and ventral wings can have markedly different pigmentation patterns. Many of the signals involved remain undiscovered, but an outline of dorsal-ventral wing formation can be pieced together. This multistep process is shown in Figure 1.
Apterous protein activates the fringe gene in the future dorsal wing region of the imaginal disc.
The Fringe protein is placed on the membrane of these cells. The activated Fringe protein signals the synthesis of the Serrate protein. The Serrate protein is placed in the cell membrane of these cells, and it binds to its receptor, Notch. The Notch protein signals the synthesis of the Wingless and Vestigial proteins. The Wingless protein is synthesized and secreted from the cell.