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Fig. 1 Mature retinal ganglion cells project dendritic arbors apically toward presynaptic partners. (A) Schematic showing retinal ganglion cells (RGCs) in the adult vertebrate retina orient their arbors toward their presynaptic partners, amacrine cells (ACs) and bipolar cells (BCs). Their synaptic contacts are confined to the inner plexiform layer (IPL). RGC axons exit basally from the cell bodies before traversing along the inner limiting membrane (ILM) and exiting the eye. Ph, photoreceptors; HC, horizontal cell; OLM, outer limiting membrane. (B) RGCs were imaged from less differentiated regions of the retina (′early′) and compared to those from more differentiated regions (′late′). Less differentiated regions were distinguished from more differentiated regions by the absence or presence, respectively, of an IPL visualized in the background of Q01 transgenic animals (red; maximum projection of three optical planes centered at the RGC soma). RGCs were labeled by transient expression of isl2b:MGFP (greyscale). Dotted line, ILM. The images in the top and bottom panels were acquired at 51 hours post-fertilization (hpf) and 60 hpf, respectively. (C) Dendritic tips, neurites > 1 μm, for the examples in (B) are marked by colored dots. The horizontal line runs parallel to the ILM and crosses the approximate center of the cell body (black dot). (D) Summary of the spatial distributions of dendritic tips for the measured population (n = number of cells). Each color represents a different cell.