Guidance of Oligodendrocyte Processes: The Role of Local Protein Synthesis

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DESCRIPTION (provided by applicant): During development of the central nervous system (CNS) post-migratory cells of both neuronal and oligodendroglial origin send out processes that navigate through the parenchyma in search for a target signal that induces their maturation, i.e. synapse formation for neuronal and myelin sheath formation for oligodendroglial cells. The regulation of this process navigation has been well characterized for neuronal cells, where a sensorimotor structure, the neuronal growth cone, located at the process tip is the "organelle" that senses environmental cues. In contrast, surprisingly little is known about oligodendroglial process pathfinding and targeting. Our preliminary data demonstrate that oligodendrocyte processes possess at their distal ends "organelles" that structurally and functionally resemble neuronal growth cones and that we will refer to as oligodendroglial growth cone-like structures (OLG-growth cones). In neurons, mRNA transport and locally restricted protein synthesis within the growth cone are considered main regulators of axon/neurite pathfinding and targeting. Our preliminary data suggest that similar regulatory mechanisms may be important for the pathfinding and targeting of oligodendrocyte processes. Thus, we formulate the central hypothesis that premyelinating, post-migratory oligodendrocytes possess OLG-growth cones that contain mRNAs, the locally restricted translation of which is critical for the regulation of oligodendroglial process pathfinding and targeting, i.e. myelination. This hypothesis will be tested in two specific aims. 1) We will determine the role of locally restricted protein synthesis for OLG-growth cone pathfinding and in particular for chemotropic turning in response to non-permissive cues. In this set of experiments the extent to which locally restricted protein synthesis occurs in pathfinding OLG-growth cones will be determined. In addition, chemotropic turning of separated processes will be analyzed after inhibition of protein synthesis. It is expected that inhibition of locally restricted protein synthesis will perturb OLG- growth cone chemotropic turning responses. 2) Using a microarray approach, we will identify mRNAs that are present in OLG-growth cones specifically in response to axonal targeting signals. This set of experiments is expected to reveal candidate proteins that are important for OLG-growth cone targeting, i.e. the initiation of myelin sheath formation. In continuing studies based on the findings of the present proposal, we are planning to further characterize these proteins. The proposed studies thus represent a first step into a set of experiments designed to better understand the regulation of oligodendrocyte process pathfinding and targeting. Such advancement in knowledge is of particular interest since deficiencies in process outgrowth and axon recognition appear to be among the main limiting factors for repair of lesions present in the CMS of patients suffering from the major demyelinating disease in humans, Multiple Sclerosis.