Patterning the vertebrate retina: the early appearance of retinal mosaics

The vertebrate retina is an extraordinary example of the modular design of the nervous tissue. Retinal neurons are organized in layers and, within each layer, cells of the same type commonly form orderly planar arrays - the retinal mosaics - which provide the basis for powerful parallel processing of the visual scene. Recent evidence indicates that the assembly of neuronal mosaics is an early event in retinal development, a finding with important implications for the control of genesis, fate determination, migration and death of developing retinal neurons.