Cell and molecular mechanisms that control cortical layer formation in the brain

Various classes of neurons in the mammalian central nervous system (CNS) migrate from their sites of origin to their final positions, where they are arranged in elaborate laminar structures. These precise patterns of neuronal alignment are disrupted in several human diseases and mouse mutants. Among them, reeler, an autosomal recessive mouse mutant discovered half a century ago, has been studied as a valuable material for investigations of neuronal layer formations. Recent identification of a gene mutated in reeler (reelin), and subsequent characterizations of other genes underlying mouse and human brain malformations have rapidly expanded our knowledge of the molecular programs underlying the normal brain layer formation. In this review, we summarize the cellular and molecular mechanisms that establish highly ordered structures in the brain, in particular in the cerebral cortex.