Figure 3:

Medulla development:

(a) Representation of the larval brain showing the OPC lying on the lateral surface of the brain, below the eye disc.

(b) In the OPC neuroepithelium cells are converted into neuroblasts that express a temporal sequence of transcription factors that generates neuronal diversity. During each window, different subtypes of neurons are produced (represented in colors). A Notch binary fate decision further increases diversity of each progeny by producing two distinct fates (striped vs non-striped neurons).

(c) Cross section of the developing larval optic lobe showing the sequential formation of the medulla. The first neuroblast produces the most posterior medulla column. Over time more neuroepithelial cells are converted into neuroblasts that will add columns to the medulla anteriorly. (d) Overlay of the temporal patterning of neuroblasts and the sequential production of medulla columns.

(e and f) Larval (e) and adult (f) schematics of the medulla representing how the regionalization of the OPC increases neuronal diversity. The uni-columnar neuron Mi1 is produced all along the OPC independently of the spatial compartments, whereas the three multi-columnar neurons Pm1,2 and 3 are only produced by progenitors from specific domains.