Motoneuron diseases are devastating in that they rob individuals of the ability to move and are often fatal due to denervation of the respiratory system. Spinal muscular atrophy (SMA) is an autosomal recessive disease that causes motoneuron dysfunction leading to paralysis and in severe cases death making it a leading genetic cause of infant/toddler mortality. Analysis of SMA animal models reveals, motor axon defects, immature neuromuscular junctions (NMJs), and denervation suggesting that changes at the motor nerve terminal may initiate disease. The survival motor neuron (SMN) gene is the genetic cause of SMA and has a clearly defined role in assembling RNAs and proteins needed for mRNA splicing (snRNP assembly). Data from our lab and others, however, suggest that SMN may have other functions that are compromised when SMN levels are decreased. Using zebrafish as a model system, we have shown that SMN has an snRNP independent function important for normal motor axon outgrowth. Moreover, we have shown that plastin 3, an actin binding protein and the first identified modifier of human SMA, can rescue motor axon defects in zebrafish caused by low Smn levels. In addition, zebrafish smn mutants have severely reduced plastin 3 levels. In this proposal we will test the hypothesis that plastin 3 acts with SMN via an snRNP independent pathway to facilitate normal motoneuron development and function. To directly test this hypothesis, we will ask whether other SMA phenotypes are rescued by plastin 3 (Aim 1). This includes motoneuron and NMJ electrophysiology, SV2 protein at the NMJ, and survival. We will determine how plastin 3 is functioning with respect to SMN by performing a structure/function analysis (Aim 2). For these experiments we will use both plastin 3 and SMN mutants to define relevant domains. We will also test the hypothesis that plastin 3 is unique in its ability to modify SMA phenotypes by examining other actin binding proteins. We will test the hypothesis that the SMN plastin 3 interaction is independent of the snRNP function of SMN (Aim 3). Lastly, we will use live imaging to ask where SMN and plastin 3 proteins localize in motoneurons and does decreasing Smn change the levels and/or cellular localization of plastin 3 (Aim 4). Data derived from these Aims will directly address the relationship between SMN and plastin 3 as it relates to SMA using a combination of electrophysiology, molecular genetics, biochemistry, cell biology, and imaging. Moreover, it would establish an snRNP- independent mechanism of SMN that directly affects motoneuron function thus greatly advancing our understanding of this disease and revealing new therapeutic targets. Using zebrafish is a strength in that we can directly analyze motoneurons in vivo in SMA models that we have developed and easily generate novel transgenics to ask specific questions. This is a unique feature of this model system and thus these studies are highly relevant and will advance our understanding of how low Smn levels cause SMA.

Public Health Relevance

Spinal muscular atrophy (SMA) is a motoneuron degenerative disease that is a leading cause of infant/toddler mortality. Low levels of the survival motor neuron (SMN) protein cause SMA, but how this happens is unclear. Recently a modifier of SMA, the actin binding protein plastin 3, was identified. Experiments in this proposal will directly test the hypothesis that SMN stabilized plastin 3 thus promoting normal motor axon outgrowth and synapses. The proposed experiments will elucidate the interaction and function of plastin 3 as it relates to SMN and has the potential to reveal novel therapeutic targets.

Agency
National Institute of Health (NIH)
Type
Research Project (R01)
Project #
5R01NS050414-10
Application #
8663318
Study Section
Neurodifferentiation, Plasticity, and Regeneration Study Section (NDPR)
Program Officer
Nuckolls, Glen H
Project Start
Project End
Budget Start
Budget End
Support Year
10
Fiscal Year
2014
Total Cost
Indirect Cost
Name
Ohio State University
Department
Neurosciences
Type
Schools of Medicine
DUNS #
City
Columbus
State
OH
Country
United States
Zip Code
43210
Biswas, Sayantanee; Emond, Michelle R; Duy, Phan Q et al. (2014) Protocadherin-18b interacts with Nap1 to control motor axon growth and arborization in zebrafish. Mol Biol Cell 25:633-42
Lyon, Alison N; Pineda, Ricardo H; Hao, le Thi et al. (2014) Calcium binding is essential for plastin 3 function in Smn-deficient motoneurons. Hum Mol Genet 23:1990-2004
McGown, Alexander; McDearmid, Jonathan R; Panagiotaki, Niki et al. (2013) Early interneuron dysfunction in ALS: insights from a mutant sod1 zebrafish model. Ann Neurol 73:246-58
Hao, Le T; Duy, Phan Q; Jontes, James D et al. (2013) Temporal requirement for SMN in motoneuron development. Hum Mol Genet 22:2612-25
Hao, Le T; Wolman, Marc; Granato, Michael et al. (2012) Survival motor neuron affects plastin 3 protein levels leading to motor defects. J Neurosci 32:5074-84
Akten, Bikem; Kye, Min Jeong; Hao, Le T et al. (2011) Interaction of survival of motor neuron (SMN) and HuD proteins with mRNA cpg15 rescues motor neuron axonal deficits. Proc Natl Acad Sci U S A 108:10337-42
Ramesh, Tennore; Lyon, Alison N; Pineda, Ricardo H et al. (2010) A genetic model of amyotrophic lateral sclerosis in zebrafish displays phenotypic hallmarks of motoneuron disease. Dis Model Mech 3:652-62
Workman, Eileen; Saieva, Luciano; Carrel, Tessa L et al. (2009) A SMN missense mutation complements SMN2 restoring snRNPs and rescuing SMA mice. Hum Mol Genet 18:2215-29
Boon, Kum-Loong; Xiao, Shu; McWhorter, Michelle L et al. (2009) Zebrafish survival motor neuron mutants exhibit presynaptic neuromuscular junction defects. Hum Mol Genet 18:3615-25
Oprea, Gabriela E; Krober, Sandra; McWhorter, Michelle L et al. (2008) Plastin 3 is a protective modifier of autosomal recessive spinal muscular atrophy. Science 320:524-7

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