Development of the commissural plate and its role in forebrain commissure development

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During development, neurons in one hemisphere of the brain connect and communicate with neurons in the opposite hemisphere. Such neural connections between the two hemispheres are called commissures, which are large bundles of axons (neural-wires) that cross the midline of the brain. There are three commissures in the forebrain: the corpus callosum, the hippocampal commissure and the anterior commissure. This wiring of the brain is essential to its proper function. When these connections don't form, the brain cannot integrate and process information in fundamental ways. Over 50 different human congenital disorders are associated with the malformation of one or more of these forebrain commissures. This proposal investigates the hypothesis that a midline structure, called the commissural plate (CP), regulates the development of all forebrain commissures. The CP was first described anatomically at the turn of the 20th century in a number of different species, and in humans in 1968. However, since this time, no papers have been published on the CP. Experiments in this proposal will use modern neuroanatomical techniques, particularly magnetic resonance imaging, molecular and mouse mutagenesis techniques, and axon guidance assays, to study the CP. We will test the hypothesis that there is something fundamentally unique about the CP as the midline crossing point for all commissural axons. We generate mouse mutants that disrupt only dorsal CP formation and then determine whether the subsequent development of the dorsal commissures occurs. We also perform molecular expression, and imaging analyses on human foetal brains. Our goal is to provide an understanding of what developmental events are disrupted in human congential disorders resulting in midline brain malformations and agenesis of the forebrain commissures. Understanding the basis of these disorders will lead to more accurate diagnoses and potentially their prevention through genetic counseling.