Fig. 3: Opposing gradients of Imp and Syp temporally pattern the OPC NE.

a–c Imp (green) and Syp (red) expression in the early (a), mid (b) and late third instar (c) larval brain. White dashed lines outline the OPC NE, yellow arrowheads indicate optic lobe (OL) NBs, and white arrowheads indicate central brain (CB) NBs. Schematics (a”’, b”’, c”’) have been created in BioRender. d Quantification of Imp (green) and Syp (red) intensities in the OPC NE from 48 to 96 h ALH. Plot illustrates the mean relative fluorescence intensity of Imp and Syp at each time point (48 h ALH n = 5 optic lobes; 60 h ALH n = 7 optic lobes; 72 h ALH n = 5 optic lobes; 84 h ALH n = 12 optic lobes; 96 h ALH n = 10 optic lobes). Error bars denote SEM. Source data are provided as a Source Data file. e–h Expression of Imp (green) and Syp (red) in the OPC NE (Arm, gray), and NBs (Dpn, magenta) in the early (e and f) and late third instar (g and h) larva. Yellow arrows denote the propagation direction of the proneural wave, and white arrowheads indicate NBs. i–n Imp (green, i), Syp (red, j), Chinmo (cyan, k), Mamo (yellow, l), Br (blue, m) and E93 (magenta, n) expression in the OPC NE (white dashed lines) at different developmental stages. Optic lobe neurons (asterisk) and the youngest neuroblast (arrowheads) are also labeled. o Schematic summary of the Imp, Syp and NE tTF expression windows in the OPC NE during medulla neurogenesis. p Schematic modeling how temporal gradients of Imp (green) and Syp (red) assign unique identities to NBs and neurons over the course of neurogenesis. Neurons are pseudo-colored based on the stage of neurogenesis in which they were generated. In all images and schematics: Medial is left. Dorsal is up in (a–c). Scale bar: 15 µm.