Genes and Therapies for Centronuclear Myopathies

The long term goals of this proposal are to identify and characterize newskeletal muscle sarcomeric genes and proteins and to understand how abnormalities of theseproteins contribute to the pathophysiology of human neuromuscular diseases. This project includescomplementary approaches to address these issues from both a basic science and reverse geneticperspective. The first involves characterization of six novel genes identified in a yeast two-hybridscreen using skeletal muscle α-actinins as bait. Characterization of one of these, called myozenin,reveals that it binds α -actinin in a number of in vitro biochemical assays and that it co-localizes atsarcomeric Z lines. Indirect immunofluorescence analysis of muscle from patients with nemalinemyopathy (NM) reveals that myozenin is abnormally localized within the nemaline rods. Additionalbiochemical and yeast two-hybrid studies on myozenin and the other new proteins will provide newinsights into Z line and thin filament structure and function. A complementary approach tounderstand these structures is to use reverse genetics to identify and characterize genes mutatedin patients with NM, a clinically and genetically heterogeneous group of inherited neuromusculardiseases distinguished by variably progressive skeletal muscle weakness and characteristic rods inmuscles of affected individuals. We have identified NM mutations in three sarcomeric genes (α-tropomyosin, nebulin and actin) to date, and have genetic data that one or more additional NMgenes must exist. Each new sarcomeric gene identified above, as well as a group of knownsarcomeric candidate genes, will be tested for mutations in NM. Finally, it is not clear how mutationsin each of the known NM genes relate to the extremely variable clinical and pathologicalphenotypes seen in this disease. To address this question of pathogenesis, global gene expressionprofiles of NM skeletal muscle from human patients and transgenic mouse models of NM will bedeveloped and interesting new skeletal muscle genes whose expression is perturbed will bestudied. Success in this project will enable accurate diagnostic and prognostic testing for all NMpatients and will shed new light on the structure and function of normal and abnormal Z lines andthin filaments in skeletal muscle.