(A) Schematic of the adult morphologies of R7 and R8 photoreceptors and lamina neurons L1–L5. The visual system comprises topographically matched modules (i.e., ommatidia, cartridges and columns). Adapted from .
(B) Axons of R7, R8, and L1–L5 are shown together within a single column as determined from serial EM reconstruction. The color of different neurons is the same as in (A). Dotted lines represent layer boundaries. Arrowheads indicate the plane of section shown in electron micrographs in (D) and (E). Courtesy of S. Takemura, I. Meinertzhagen, and L. Scheffer (JRC/HHMI).
(C) Examples of three general classes of medulla neurons that are synaptic targets for R7, R8, and L1–L5 neurons (two examples are shown for each class). Within each class, there are many cell types that display similar morphologies and branch in different layers. Adapted from .
(D and E) Cross-sections through medulla columns reconstructed by serial EM within the M2 and M3 layers (see arrows in B). Axons are colored as in (A) and (B). Each column contains processes from over 100 different neuronal cell types (A. Nern, personal communication). Scale bar, 2 µm. Courtesy of S. Takemura, I. Meinertzhagen, and L. Scheffer (JRC/HHMI).
(F and G) Isolation of R8 neurons at 40 hr APF using fluorescence-activated cell sorting (FACS). Only R8 neurons express both retinal-specific TdTom and R8-specific GFP. Senseless is an R8-specific transcription factor. Scale bars, 10 µm. In (F), arrows indicate double-labeled cells in developing tissue and the asterisks indicate single GFP-labeled cells of different cell types (i.e., contaminants).
(H and I) Isolation of L3 neurons at 40 hr APF using FACS. Only L3 neurons express lamina-specific TdTom and L3-specific GFP. Scale bars, 10 µm. In (H), arrows indicate double-labeled cells in developing tissue and the asterisks indicate single GFP-labeled cells of different cell types (i.e., contaminants). See Experimental Procedures for purification protocols for other cells and additional details.