Figure 4.

Tiling and column formation in the vertebrate retina. The retina develops into a laminated structure with the cell bodies, axons, and dendrites of specific cells segregated to specific layers. The IPL is further subdivided into multiple lamina labeled S1–S5 as done in [35••]. In general, the dendrites of cells of the same type do not overlap and the cell somas are evenly space, forming a mosaic that tiles the retina. (Top) In classes of ACs this is due to a repellent activity of DSCAM. (Middle) HCs have evenly spaced cell soma, although the dendrites significantly overlap. Huckfeldt et al. show that HCs make vertical, transient projections that repel each other such that they become evenly spaced. (Bottom) The chick IPL can be divided into five layers. Lock and Key models for lamination predict that each pre-synaptic and post-synaptic cell expresses complementary adhesion molecules. Homotypic adhesions are expressed in specific lamina and have been shown to be necessary and sufficient for proper lamination. These four proteins cannot explain all of lamination; other mechanisms remain to be elucidated. (ONL: Outer Nuclear Layer; OPL Outer Plexiform Layer; INL: Inner Nuclear Layer; IPL: Inner Plexiform Layer; GCL: Ganglion Cell Layer; PRs: photoreceptors; HCs: horzontal cells; BPCs: bipolar cells; ACs: amacrine cells; RGCs: retinal ganglion cells). Bottom left adapted from [35••].