Robert Sealock, PhD
Professor

Education:

PhD, Purdue University 1972

Cell Biology of the Neuromuscular Junction and of Dystrophin -Associated Proteins

We are interested in two mutually reinforcing problems of the cell biology of skeletal muscle surface membrane, or sarcolemma. The first is the cell biology of the formation and maintenance of the neuromuscular junction: recruitment of acetylcholine receptors and other specialized proteins, proper localization of these proteins on the postsynaptic membrane, identification of the associated submembrane protein machinery, and elaboration of the junctional folds and their functions.  The second concerns the functions of dystrophin, utrophin, and the proteins of the dystrophin/utrophin-associated complex.  Dystrophin is the protein whose absence causes Duchenne muscular dystrophy, a major human genetic disease of muscle wasting. A large cytoskeletal protein, it is a key element in linking cortical actin skeleton in the muscle cell to extracellular basal lamina via a large complex of cytoplasmic and transmembrane proteins including the dystrobrevins, the dystroglycans, and the sarcoglycans.  Mutations in many of these dystrophin-associated proteins also cause human muscular dystrophies.  Agrin, a protein secreted by motor nerves which causes assembly of acetylcholine receptors at the junction site, interacts with dystroglycan, and a close homolog of dystrophin, utrophin, is precisely localized within the neuromuscular junction.  Finally, multiple gene targeting deletions in mice have established the importance of several dystrophin/utrophin-associated proteins for proper structure and function of the junction.  Thus, our studies have the potential to contribute to two major questions in cell biology and human health simultaneously.

(click for larger image and description)

Our efforts are now focused on the roles of these protein families in postnatal maturation and maintenance of the NMJ using a fusion of a genetic approach with our historical morphological approaches. The particular focus at present is on the syntrophin family of dystrophin-, utrophin- and dystrobrevin-associated scaffolding proteins. The genetic approach involves rescue of aberrant development caused by gene targeting (knockout) of critical proteins and perturbation of normal postnatal development of the junction. The rescue aims are accomplished by controlled-level and controlled-timing transgenic expression in null mice of full length versions of rescue proteins or selected domains, homologs, or chimeras thereof. The results are analyzed biochemically and morphologically (conventional and confocal light microscopy, electron microscopy, immunolocalization and quantitation of proteins, etc.). The perturbation experiments likewise involve transgenic expression of dominant negative forms of proteins believed to function in postnatal maturation and maintenance of the junction. With these approaches, we expect to dissect signaling pathways and cytoskeletal networks at the NMJ and to contribute to identification of the activities of the dystrophin-associated protein families which are so critical to human skeletal muscle health.

Publications:

Jenkins SM, Kizhatil K, Kramarcy NR, Sen A, Sealock R, Bennett V (2001). FIGQY phosphorylation defines discrete populations of L1 cell adhesion molecules at sites of cell-cell contact and in migrating neurons. J Cell Sci. 114(Pt 21):3823-35.

Adams, M. E., N. R. Kramarcy, S. P. Krall, S. Rossi, R. L. Rotundo, R. Sealock, and S. C. Froehner (2000). Absence of a-syntrophin leads to structurally aberrant neuromuscular synapses deficient in utrophin. Journal of Cell Biology 150:1385-1398.

Kramarcy, N. R., and R. Sealock (2000). Syntrophin isoforms at the neuromuscular junction: Developmental time course and differential localization. Molecular and Cellular Neuroscience 15:262-274.

Peters, M. F., H. M. Sadoulet-Puccio, R. M. Grady, N. R. Kramarcy, L. M. Kunkel, J. R. Sanes, R. Sealock, and S. C. Froehner (1998). Differential membrane localization and intermolecular associations of a-dystrobrevin isoforms in skeletal muscle. Journal of Cell Biology 142:1269-1278.

Gee, S. H., R. Madhavan, S. R. Levinson, J. H. Caldwell, R. Sealock, and S. C. Froehner (1998). Interaction of muscle and brain sodium channels with multiple members of the syntrophin family of dystrophin-associated proteins.  Journal of Neuroscience 18:128-137.

Sealock, R., and S. C. Froehner (1996). The dystrophin family, agrin, and the construction of the neuromuscular junction. In: Dystrophin: Gene, Protein, and Cell Biology. S. Brown and J. A. Lucy, eds. Cambridge University Press, Cambridge, UK. pp. 139-162.

Kramarcy, N. R., A. Vidal, S. C. Froehner, and R. Sealock (1994). Association of utrophin and multiple dystrophin short forms with the mammalian M_r 58,000 dystrophin-associated protein (syntrophin). Journal of Biological Chemistry 269:2870-2876.

Sealock, R., and S. C. Froehner. (1994). Dystrophin-associated proteins and synapse formation: Is a-dystroglycan the agrin receptor? Cell 77:617-619.