Notch signaling is not sufficient to define the affinity boundary between dorsal and ventral compartments

The developing limbs of Drosophila are subdivided into distinct cells popul ations known as compartments. Short-range interaction between cells in adja cent compartments induces expression of signaling molecules at the compartm ent boundaries. In addition to sewing as the sources of long-range signals, compartment boundaries prevent mixing of the adjacent cell populations. On e model for boundary formation proposes that affinity differences between c ompartments are defined autonomously as one aspect of compartment-specific cell identity. An alternative is that the affinity boundary depends on sign aling between compartments. Here, we present evidence that the dorsal selec tor gene apterous plays a role in establishing the dorsoventral affinity bo undary that is independent of Notch-mediated signaling between dorsal and v entral cells.