Download a zebrafish model of myotubular myopathy

A ZEBRAFISH MODEL OF MYOTUBULAR MYOPATHY.
JJ Dowling, AP Vreede, EM Gibbs, EL Feldman. University of Michigan, Ann Arbor, MI
Background: Myotubular Myopathy is a congenital myopathy that is one of the most severe neurologic
disorders of childhood. It is caused by mutations in the myotubularin (MTM1) gene. In vitro, MTM1
functions as a lipid phosphatase that dephosphorylates specific phosphoinositides (PIs). Via its ability to
modify PIs, MTM1 serves as a critical regulator of several processes, most notably endocytosis and
membrane trafficking, in several cell culture and invertebrate systems. However, its function in vertebrates
and specifically in muscle development and homeostasis is poorly understood. MTM1 is a member of a
large group of homologous proteins referred to as myotubularin related proteins (MTMRs). Several
MTMRs are also associated with neurologic disease, and these conditions are part of a growing group of
disorders that are due to abnormalities in proteins that regulate membrane trafficking processes. As with
MTM1, there remains a limited understanding of the association between the proposed functions of these
proteins, normal development, and the pathogenesis of disease.
Objectives: Using the zebrafish as a model system, determine the function(s) of MTM1, the relationship of
these functions with the development of muscle disease, and the redundancy of MTMRs.
Design/Method: Knockdown of MTM1 is accomplished using morpholino antisense technology in
developing zebrafish embryos. Morphant embryos are compared to controls using various histopathologic
metrics to determine MTM1 gene function. Morpholinos are combined with MTMR RNAs to determine
functional redundancy.
Results: We demonstrate that MTM1 is required for muscle development and muscle function in the
zebrafish. Loss of MTM1 causes histopathologic changes reminiscent of myotubular myopathy. It also
results in increases in PI3P levels. In addition, we show that MTMR1 but not MTMR2 can functionally
compensate for the loss of MTM1.
Conclusions: Morpholino knockdown of MTM1 in the zebrafish reproduces the features of myotubular
myopathy. Using this model system, we demonstrate that MTM1 is required for specific aspects of muscle
function and acts as a lipid phosphatase. Additionally, we address the question of functional redundancy
among MTMRs by showing that MTMR1 and not MTMR2 can rescue the morphant phenotype.