Department of Neuroscience
Professor of Neuroscience
College of Medicine
Department of Neuroscience
Rightmire Hall Room 060
Research Lab: Brown Lab
Research Area: We are investigating axonal transport and the cytoskeleton of nerve cells.
Most cytoskeletal and cytosolic proteins are synthesized in the cell body of nerve cells and transported along their axons by slow axonal transport. This movement is essential for axonal growth and survival and continues throughout the life of neurons, but the mechanism is poorly understood.
Our research focuses on neurofilaments, which are one of three classes of cytoskeletal polymers that comprise the neuronal cytoskeleton. Neurofilaments, which are the intermediate filaments of nerve cells, are structural elements that play a major role in the expansion of axonal caliber. In large myelinated axons they are the most abundant cytoplasmic structure, occupying most of the axonal volume.
In addition to this structural role, we have shown that neurofilaments are also cargoes of axonal transport, unique among the known cargoes of axonal transport because they are flexible protein polymers just 10 nm in diameter but many micrometers in length. These polymers move rapidly both forwards and backwards along microtubule tracks, powered by kinesin and dynein motors. The movements are fast but the average velocity is slow because the polymers spend most of their time pausing. Thus the balance of movements and pauses is a critical determinant of neurofilament distribution along axons.
Recently we have discovered that the moving and pausing behavior of neurofilaments is influenced by their length, and that this in turn is regulated by a dynamic cycle of severing (which shortens the polymers) and end-to-end joining (which lengthens them). We are fascinated by the relationship between these novel dynamic properties of neurofilaments and their structural role in axonal architecture and morphology.
The transport and organization of axonal neurofilaments are also of clinical interest because these polymers accumulate abnormally in axons in many neurodegenerative diseases, leading to axonal swellings. We believe that such accumulations arise due to perturbations of the kinetics of neurofilament transport. Mutations in neurofilament protein also cause one form of Charcot-Marie-Tooth disease, which is the most common form of inherited peripheral neuropathy, but the molecular mechanism is unknown.
Currently we are using state-of-the-art live-cell fluorescence imaging techniques in combination with molecular, biochemical and ultrastructural approaches to investigate the movement and organization of neurofilaments in cultured nerve cells and in vivo. Our long-term goal is to understand the mechanisms that regulate the transport and function of axonal neurofilaments in health and disease.
Microscopy: wide-field and confocal fluorescence, phase contrast and DIC microscopy of living cells; immunofluorescence light microscopy; transmission electron microscopy
Digital imaging: multi color time-lapse fluorescence imaging; kymograph and motion analysis; movie processing; quantification of fluorescence; general digital image processing and analysis
Cell culture: culture of central and peripheral neurons from rats and from wild type and mutant mice; myelinating co-cultures; nuclear and cytoplasmic microinjection; transfection with plasmid expression vectors
Ex vivo imaging: confocal fluorescence microscopy of peripheral nerves from transgenic mice expressing fluorescent proteins
Biochemistry: purification and covalent modification of cytoskeletal proteins; SDS-PAGE; Western blotting; co-immunoprecipitation assays
Molecular biology: construction of plasmid vectors encoding fluorescent-fusion proteins; site directed mutagenesis
Education and Training:
PhD, King’s College, University of London, 1987
Postdoctoral Training: Case Western Reserve University and Temple University, 1987-1993