Molecular Specializations of the Axonal Cytoskeleton

S. T. Brady, Ph.D.The neuron represents a unique model for addressing fundamental questions in cell and molecular biology. The size, shape, and specialized functions of neurons permit analyses of cell differentiation and intracellular dynamics.

Our research addresses four areas:

1) Molecular Mechanisms of Axonal Transport;
2) Specialization of the Neuronal Cytoskeleton;
3) Glial Modulation of Neuronal Function; and
4) Effects of Physiological Stress on Neurons.

These studies illuminate mechanisms underlying neuronal function, regeneration, pathogenesis in neurodegenerative diseases, and neuronal responses to environmental factors or in diseases such as multiple sclerosis.Neuronal and nonneuronal cells require ordered transport and targeting of membrane organelles. We discovered a new class of mechanochemical enzymes, kinesins, which serve as motors for organelle transport. Current research addresses basic questions regarding the cell and molecular biology, biophysics, and neurobiology of the kinesins. Projects include expression of kinesin isoforms; mutagenesis of kinesin subunits for biochemical and structural features; identification of kinesin receptor(s); and characterization of regulatory mechanisms for both kinesin motility and binding to organelles; and roles played by kinesin related proteins in neuronal differentiation.

Specialization of the neuronal cytoskeleton is critical to establishment of connections and maturation of the nervous system. Our studies focus on molecular specializations of the axonal cytoskeleton, including unique posttranslational modifications of tubulin. Such specializations affect axonal plasticity and neuronal morphologies. Quantitative and qualitative changes in the axonal cytoskeleton are being evaluated with a goal of understanding molecular mechanisms in neuronal cytoskeletal function and neuropathology.Communication between glia and axon is more complex than previously recognized, suggesting that glia play major roles in sculpting the functional architecture of neurons. We previously showed that myelination affects slow axonal transport, regeneration and neurofilament organization. Microenvironmental cues from glia and target cells may also target proteins to specific domains of a neuron, including delivery of synaptic vesicles to terminals and sodium channels to nodes of Ranvier. Glial modulation of neuronal function is being evaluated. Comparing the effects of CNS and PNS myelination on neurons shows how different glial environments affect the nervous system. Mutant and transgenic mouse models are being used to define interactions between glia and neurons and to identify signal transduction pathways for modulation of neuronal function by myelinating glia.

Finally, neurological problems have been associated with chronic stress and extended exposure to elevated glucocorticoids, which include persistent changes in motor, hypothalamic and sensory function. Such changes may involve both functional and morphological alterations in the brain, but underlying mechanisms are unclear. Physiological stress is commonly associated with a wide range of human activities, but much less attention has been paid to the effects of modest chronic stress than of acute stress. Stress may alter homeostatic mechanisms for maintaining neuronal function and many stress-related effects resemble changes in the aging nervous system. These studies analyze the effects of elevated corticosteroids on the dynamics of the neuronal cytoskeleton, synaptic function and vesicle trafficking in a mouse model.

Selected References

Morfini, G., Szebenyi, G., Brown, H., Pant, H. C., Pigino, G., DeBoer, S., Beffert, U., and Brady, S. T. (2004). A novel CDK5-dependent pathway for regulating GSK3 activity and kinesin-driven motility in neurons. EMBO J 23: 2235-2245.

U.Beffert, E. Weeber, G. Morfini, J. Ko, S.T. Brady, L.-H. Tsai, J.D. Sweatt, and J. Herz (2004) Reelin and Cdk5 dependent signals cooperate in regulating neuronal migration and synaptic transmission. J. Neurosci. 24:1897-1906

G. Pigino, G. Morfini, M.P. Mattson, S.T. Brady, and J. Busciglio (2003) Alzheimer’s Presenilin 1 Mutations Impair Kinesin-based Axonal Transport. J. Neurosci. 23:4499–4508

G. Szebenyi, G. Morfini, A. Babcock, M. Gould, K. Selkoe, D.L. Stenoien, P. Faber, M. MacDonald, M. McPhaul, and S.T. Brady (2003) Neuropathogenic Forms of Huntingtin and Androgen Receptor Inhibit Fast Axonal Transport. Neuron 40:41-52.

G. Morfini, G. Szebenyi, R. Elluru, N. Ratner, and S.T. Brady (2002) Glycogen Synthase Kinase 3 Phosphorylates Kinesin Light Chains and Negatively Regulates Kinesin-based Motility. EMBO J. 23:281-293

M.J. Donelan, G. Morfini, R. Julyan, S. Sommers, L. Hays, H. Kajio, I. Briaud, R.A. Easom, J.D. Molkentin, S.T. Brady, and C. J. Rhodes (2002) Ca2+-Dependent Dephosphorylation of Kinesin Heavy Chain on ß-Granules in Pancreatic ß-cells: Implications for Regulated ß-granule Transport and Insulin Exocytosis. J. Biol. Chem. 277: 24232-24242

U. Beffert, G. Morfini, H. Bock, H. Reyna, S.T. Brady and J. Herz (2002) Reelin Mediated Signaling Locally Regulates PKB/Akt and GSK-3ß. J. Biol. Chem 277:49958–49964

G. Pigino, G. Morfini, M.P. Mattson, S.T. Brady, and J. Busciglio (2003) Alzheimer’s Presenilin 1 Mutations Impair Kinesin-based Axonal Transport. J. Neurosci. 23:4499–4508

G. Szebenyi, G. Morfini, A. Babcock, M. Gould, K. Selkoe, D.L. Stenoien, P. Faber, M. MacDonald, M. McPhaul, and S.T. Brady (2003) Neuropathogenic Forms of Huntingtin and the Androgen Receptor Inhibit Fast Axonal Transport. Neuron (in press).

S. Roy, P. Coffee, G. Smith, R.K.H. Liem, S.T. Brady and M.M. Black (2000) Neurofilaments are Transported Rapidly but Intermittently in Axons: Implications for Slow Axonal Transport. J. Neuroscienc 20:6849-6861.

M.-Y. Tsai, G. Morfini, G. Szebenyi and S.T. Brady (2000) Modulation of Kinesin-Vesicle Interactions by Hsc70: Implications for Regulation of Fast Axonal Transport. Molec. Biol. Cell 11:2161-2173.

S.T. Brady, L.L. Kirkpatrick, A. Witt, S. de Waegh, C. Readhead, P.H. Tu and V.M.-Y. Lee (1999) Formation Of Compact Myelin Is Required For Maturation of the Axonal Cytoskeleton. J. Neuroscience 19:7278-7288

J.D. Huang, S.T. Brady, B.W. Richards, D. Stenoien, J.H. Resau, N.G. Copeland, and N.A. Jenkins (1999) Direct Interaction of Microtubule- and Actin-based Transport Motors. Nature 397:267-270.

N. Ratner, G.S. Bloom, and S.T. Brady (1998) A Role for Cdk5 Kinase in Fast Anterograde Axonal Transport: Novel Effects of Olomoucine and the APC Tumor Suppressor Protein. J. Neuroscience 18:7717-7726.

Sack, S., J. Muller, A. Marx, M. Thormahlen, E. M. Mandelkow, S. T. Brady and E. Mandelkow (1997) X-ray structure of motor and neck domains from rat brain kinesin. Biochemistry 36:16155-16165.

D.S. Stenoien and S.T. Brady (1997) Immunochemical analysis of kinesin light chain function. Molec. Biol. Cell 8:675-689.

S.T. Brady (1995) Biochemical and Functional Diversity of Microtubule Motors in the Nervous System. Curr. Opinion Neurobiol 5:551-558.


Professor and Head Anatomy & Cell Biology
B.S., MIT, 1973.
Ph.D., University of Southern California, 1978.

Scott T. Brady, Ph.D.