L1 Interactions in Retino-Collicular Targeting

University Of North Carolina At Chapel Hill, Chapel Hill NC

Investigators

Abstract

Abstract Guidance and targeting of neuronal axons from the eye to the brain is orchestrated through a diverse set of cues by molecular mechanisms that are just beginning to be elucidated. This proposal focuses on the mechanism by which the neural cell adhesion molecule L1, regulates the retinotopic map of retinal ganglion cell axons to targets in the brain. The specific hypothesis to be tested is that L1 linkage to the cytoskeleton through ankyrin is an esssential mechanistic determinant by which ganglion cell axons are mapped to topographically specific targets in the superior colliculus to specify visual connectivity. The role of L1 interactions with the neuronal cytoskeleton in synaptic targeting will be tested in a novel L1 mutant mouse L1(Y1229H), which lacks the capability to bind ankyrin, an adapter that links L1 to the actin cytoskeleton. This mutant is the first example of a point mutation disrupting a specific cytoskeletal linkage that perturbs topographic axon mapping. In Aim 1 axon tracing of retinal ganglion cell axons to topographic targets in the superior colliculus of L1(Y1229H) knock-in mice will be carried out to define the pattern of retinotopic mapping along both the anteroposterior and mediolateral axes in order to obtain insight into the role of L1 anchorage to the cytoskeleton in axonal outgrowth and synaptic targeting. In Aim 2, cellular and biochemical assays will identify the protein interactions governed by L1 binding to the cytoskeleton necessary for axonal targeting and synaptic contact formation. Specific experiments are designed to analyze L1-ankyrin binding effects on modulation of integrin-dependent cell adhesion and attractive or repulsive axon guidance to ephrins and Eph receptors (both A and B classes). The interaction of L1 neural adhesion molecules with ankyrin and ephrin/Eph receptors is a novel concept that will advance a molecular understanding of mechanisms that regulate neuronal wiring. This study has broad significance for understanding fundamental mechanisms of neuronal wiring, because L1 is the prototype of a family of adhesion receptors that are widely expressed in the brain, where they may mediate synaptic connections through different ankyrin isoforms. Educational benefits will include training of 2 undergraduates, 2 graduate students, and a postdoctoral scientist. The grant will increase the participation of women in research, enhancing diversity and minority representation, as all of the trainees are women. General benefits to the society at large will include provision of new knowledge that will increase understanding of fundamental mechanisms of neuronal connectivity. This knowledge will impact broadly on larger areas of nerve regeneration and nerve grafting, and may suggest new means to improve the life and health of animals and human beings.