A permissive role of Notch in maintaining the DV affinity boundary of the Drosophila wing.

Cell affinities can contribute to organizing cells into tissues and organs. Drosophila limbs and the vertebrate central nervous system are subdivided into adjacent populations that do not mix. These cell populations are called compartments. Cell interactions mediated by receptor Notch have been implicated in the specification of compartment boundaries. However, the contribution of Notch in this process remains controversial. The instructive role of Notch and the transcriptional requirement of the pathway have been questioned in the last few years. Due to its central role in making developmental boundaries in vertebrates and invertebrates, we have reevaluated the contribution of Notch and its signaling pathway in the maintenance of an affinity difference between dorsal (D) and ventral (V) compartments in the Drosophila wing. Here we present evidence that unrestricted, low levels of Notch are sufficient for the formation of a stable DV affinity boundary. Cleavage of the Notch protein, release of the intracellular domain and a transcriptional function of Notch via the Suppressor of Hairless transcription factor are required and sufficient in this process. Our data support a permissive role of Notch in maintaining the DV affinity boundary. This contrasts with the instructive role of Notch in executing the organizing activity of the DV boundary.