Figure 2:

Building the retinotopic map in the lamina:

(a) Retinotopic organization of the visual system. Colors represent three different retinotopic points along the A-P axis. Examples of neurons from the different neuropiles that are retinotopically organized (L2 in the lamina, Mi1 in the medulla and T4 and T5 in the lobula complex).

(b) Sequence of lamina differentiation during larval development: the entry of photoreceptor axons into the lamina lead to the division of Lamina Precursors Cells (LPCs) and their assembly into lamina columns. This is followed by the entry of wrapping glia cell processes that will direct the differentiation of LPCs into differentiated lamina monopolar cells. As the eye disc grows more photoreceptor axons (in red) and glial cells enter the lamina leading to more columns being assembled posteriorly following a front of differentiation. Note that L5 neurons at the bottom of the lamina follow a different sequence than the other lamina neurons and do not depend on signaling from wrapping glia.

(c) Schematic of the signaling activities required for the formation and differentiation of lamina neurons. (d) Schematic of the adult lamina. Note that each lamina cartridge is composed of one copy of each of the 5 lamina monopolar cells and 6 outer photoreceptors (R1-6).