Figure 3. Temporal window of origin and birth order of medulla neurons.
(a) Left: Frontal view of L3 medulla NBs sequentially expressing the indicated tTFs. Right: Schematic of tTF expression as medulla neuroblasts age, based on immunostaining. Dashed lines represent predicted temporal windows.
(a’) Left: Sagittal section of L3 medulla cortex showing the expression of the concentric genes Bsh, Run, Vvl and Toy, and the tTF Slp. Early born neurons are located closer to the medulla neuropil, while later born neurons are farther. Right: Schematic of concentric gene expression in medulla neurons activated and maintained through different temporal windows.
(b) Sagittal sections of optic lobes showing the expression of concentric genes at L3 stage. Anterior is to the right and posterior to the left. Earlier born neurons are located closer to the medulla neuropil (dashed crescent). Early, middle and late subdivisions are based on the predicted temporal windows when a given concentric gene starts to be expressed. Medulla neurons that express the corresponding concentric gene are indicated below each panel. Tj (ix) and Fork head (Fkh:GFP) (x) expression is restricted to specific regions of the medulla cortex. Hbn (xii) is also expressed in lamina wide-field neurons (Lawf1-2, arrowheads) that originate from the Dpp regions of the lamina neuroepithelium and migrate along the medulla neuropil38. Dll (xiv) is also expressed in medulla neuropil glia (mng, arrowhead)22.
(c) UMAP plot showing differently colored medulla clusters from the P15 dataset indicating groups that share concentric gene expression within a given temporal window. Cluster identity is indicated when known.
(d) Schematic representing tTF expression in medulla NBs and GMCs and downstream concentric gene expression in neurons. Neurons and glia predicted to be generated in each temporal window are indicated. Neurons sharing the same Notch status generated in the same temporal window express the same neurotransmitter (NT).
Scale bar: 10 μm