Figure 2. Recognition events requiring cell identity.

A neuron's identity specifies its proper position in a circuit. Neurons in the retina must recognize appropriate heterotypic cells in order to form functional connections within the retina (B) and in central targets (D). They must also recognize homotypic cells in order to maintain mosaic spacing (C). These recognition events require cell-type specific molecules, and the molecules required for each type of recognition may be different. Therefore, homotypic cells share a repertoire of cell-type specific recognition and adhesion molecules. At interactions between homotypic cells, inappropriate adhesions must masked to prevent excessive fasciculation and to maintain proper dendrite arborization.