Fig. 2: Delta represses Notch activity at the wavefront.

a N activity (NRE-dVenus, white) is elevated in cells adjacent to Dl-expressing clones (Ay-Gal4 UAS-Dl, magenta), and is autonomously repressed (arrows). Yellow arrow indicates endogenous Dl expression at the wavefront (Lsc, blue). White and magenta signals are enhanced. b, c Results of numerical simulations using step function (b) and Hill function (c). Left panels show the two-dimensional patterns of N and D. Right panels are the one-dimensional plots of N (green), D (magenta), E (black), and A (blue; y = 13). The values of N, D, and E are 30, 10, and 10 times multiplied, respectively. Reduced production rate of D causes single peak of N activity (a_d = 0.5). d optix-Gal4 expression in the dorsal and ventral subdomains of the optic lobe (green). e, f Changes in N activity (NRE-dVenus, green) upon Dl RNAi under the control of optix-Gal4. Dl (magenta) and Lsc (blue). The signal intensities of NRE-dVenus, Dl, and Lsc within the white (control) and yellow boxes (Dl RNAi) are plotted in the right panels. Asterisks indicate the optix-Gal4 positive areas outlined by white lines. e Partial Dl knockdown causes the fusion of the twin peaks of N activity (yellow box, arrows). f Strong Dl knockdown causes the loss of Dl expression and N activity (yellow box). g A schema illustrating trans-activation and cis-inhibition at the wavefront. h Expression level of full-length N (white) is reduced behind the wavefront (Lsc, blue). Signal intensities of N (black) and Lsc (blue) within the white box are plotted in the right panel. Arrows indicate the reduction of N expression level. i, j Expression level of full-length N (white) is upregulated in Dl mutant clones visualized by the absence of GFP (green in i, blue in j) behind the wavefront (Lsc, blue). i Signal intensities of N (black) within the dotted box are plotted in the right panel. Arrow indicates the upregulation of N expression level. j N (magenta) is accumulated along the cell membrane (Ecad, green) in Dl mutant clones. The dotted box is magnified in the right panel. Scale bars indicate 20 μm.