Figure 1.

(a) Patterning of the Drosophila notum. Drosophila pupal hemi-notum expressing shotgun-GFP (shgGFP, labels all apical cell boundaries) and neuralized-GMCA (GFP-tagged F-actin reporter expressed in SOPs). At the onset of patterning (12 h after pupariation (AP)), few cells are neuralized-GMCA positive. By 24 h AP, the tissue is patterned with a sparse, ordered distribution of SOPs. Scale bar, 50 µm. Anterior is to the right in all images. (b) Visualization of basal protrusions in SOPs. Basal z-projections (less than or equal to 10 µm) of SOPs expressing a GFP-tagged F-actin reporter under the neuralized-GAL4 driver. Scale bar, 10 µm. (c) Schematic of Delta (purple) Notch (green) and Notch reporter (R) interactions. When Delta (D) binds to Notch (N) in trans, it activates the intracellular part of the Notch receptor (R) to inhibit Delta production in the receiving cell. Notch–Delta interactions within the same cell (cis interactions) lead to inactivation of both the ligand and the receptor. (d) Notch–Delta interactions engaged in trans-inhibition instead of trans-activation of the Notch receptor. (e) Notch–Delta-mediated lateral inhibition gives rise to salt-and-pepper spatial patterns. Protrusion signalling results in sparser patterns. (f) Schematic of protrusions in our model. (g) Modelling protrusion polarization and interactions. (i) A scenario where the protrusions of two cells are within range of one another, but do not overlap due to polarization. (ii) Successful protrusion-mediated interactions between two cells. The area of potential contact is shaded. More details are provided in the Methods section.