Roles of proteoglycans in neuronal circuit formation of retinotectal projections

The formation of neuronal circuits has long been considered as one of the basic problems in the developmental neurobiology; projections from the retina to their higher center, the tectum in nonmammalian vertebrates and the superior colliculus in mammals, are the most feasible for the experimental approaches. The recent investigations have shown that a series of guidance cues along the pathways sequentially navigates the retinal axons step by step. At the decision points along the retinal pathway, steering of the retinal axons is controlled by proteoglycans and their carbohydrate chains: chondroitin sulfate proteoglycans and heparan sulfate proteoglycans.