Regulation of Neurofilament Expression During Axon Outgrowth

Suny At Albany, Albany NY

Investigators

Abstract

Frogs, along with fish and other amphibians, can successfully recover from brain injuries that would leave mammals (including humans) permanently disabled. Successful recovery from such injuries requires neurons to coordinate the expression of multiple functionally inter-related proteins that participate in rebuilding the damaged nerves. Understanding which of these changes in gene expression are important for successful nerve regrowth is facilitated by comparing nerve regeneration with development. The visual system of the South African claw-toed frog is a good system for such studies because its optic nerve can regenerate throughout life and a large amount of baseline data already exist for both optic nerve regeneration and development. Neurofilaments are one of the major intracellular structural components of neurons. They are made from subunit proteins whose expressions emerge successively in a characteristic pattern during both nerve regeneration and development. During nerve outgrowth, expression of the different neurofilament proteins must be tightly coordinated to avoid the formation of harmful aggregates. One neurofilament subunit protein found in virtually all vertebrate species is the middle-sized subunit, more commonly known as NF-M. In all vertebrates that successfully repair injuries to the brain and spinal cord (i.e., lampreys, fishes, and frogs), NF-M expression changes in a characteristic pattern not seen in animals that fail to recover from such injuries (i.e., birds, reptiles, and mammals). The premise of this proposal is that understanding at the molecular level how this changing expression is controlled during successful optic nerve regeneration and development will lead to a deeper understanding of how neurons successfully reactivate developmental programs that lead to successful recovery from trauma. The first experimental objective is to evaluate during optic nerve regeneration the control points in NF-M gene expression that are most active, from the initial reading of the gene to the synthesis of the protein itself. Preliminary data indicate significant changes occur at the level of protein synthesis and have implicated the involvement of several proteins known to regulate protein synthesis in other systems. After the analysis is completed for NF-M, it will be repeated for the other neurofilament subunit proteins to identify shared regulatory mechanisms and proteins. The second objective is to evaluate the effects of suppressing during development the expression of one of the proteins already implicated in controlling NF-M expression. Preliminary data indicate that without this protein, developing neurons not only fail to make NF-M protein, but also fail to make nerves. How this happens at the molecular level, as well as the functional consequences during nerve development of blocking expression of other proteins implicated in NF-M expression will also be examined. Results are expected to provide new insights into how the nervous system reactivates developmental programs that lead to successful repair of brain injury. The broader educational impacts of this work are that it will contribute to the nation's scientific infrastructure through the training of two PhD students and undergraduates at a public institution with a culturally diverse student body. Spinoffs from this work will have an impact on student exercises in an undergraduate laboratory course in Developmental Biology, and on the lectures, readings, and discussions of three courses in Molecular Biology, Developmental Neurobiology, and Molecular Neurobiology taught by the principal investigator.