title: Interaction of survival of motor neuron (SMN) and HuD proteins with mRNA cpg15 rescues motor neuron axonal deficits.
abstract: Spinal muscular atrophy (SMA), caused by the deletion of the SMN1 gene, is the leading genetic cause of infant mortality. SMN protein is present at high levels in both axons and growth cones, and loss of its function disrupts axonal extension and pathfinding. SMN is known to associate with the RNA-binding protein hnRNP-R, and together they are responsible for the transport and/or local translation of β-actin mRNA in the growth cones of motor neurons. However, the full complement of SMN-interacting proteins in neurons remains unknown. Here we used mass spectrometry to identify HuD as a novel neuronal SMN-interacting partner. HuD is a neuron-specific RNA-binding protein that interacts with mRNAs, including candidate plasticity-related gene 15 (cpg15). We show that SMN and HuD form a complex in spinal motor axons, and that both interact with cpg15 mRNA in neurons. CPG15 is highly expressed in the developing ventral spinal cord and can promote motor axon branching and neuromuscular synapse formation, suggesting a crucial role in the development of motor axons and neuromuscular junctions. Cpg15 mRNA previously has been shown to localize into axonal processes. Here we show that SMN deficiency reduces cpg15 mRNA levels in neurons, and, more importantly, cpg15 overexpression partially rescues the SMN-deficiency phenotype in zebrafish. Our results provide insight into the function of SMN protein in axons and also identify potential targets for the study of mechanisms that lead to the SMA pathology and related neuromuscular diseases.
authors.affiliation: The F.M. Kirby Neurobiology Center, Department of Neurology, Children's Hospital Boston, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Bikem
authors.initials: B
authors.lastname: Akten
authors.forename: Min Jeong
authors.initials: MJ
authors.lastname: Kye
authors.forename: Le T
authors.initials: le T
authors.lastname: Hao
authors.forename: Mary H
authors.initials: MH
authors.lastname: Wertz
authors.forename: Sasha
authors.initials: S
authors.lastname: Singh
authors.forename: Duyu
authors.initials: D
authors.lastname: Nie
authors.forename: Jia
authors.initials: J
authors.lastname: Huang
authors.forename: Tanuja T
authors.initials: TT
authors.lastname: Merianda
authors.forename: Jeffery L
authors.initials: JL
authors.lastname: Twiss
authors.forename: Christine E
authors.initials: CE
authors.lastname: Beattie
authors.forename: Judith A J
authors.initials: JA
authors.lastname: Steen
authors.forename: Mustafa
authors.initials: M
authors.lastname: Sahin
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001369:Axons / Q000378:metabolism* / Q000473:pathology*; D002478:Cells, Cultured; D051959:ELAV Proteins / Q000235:genetics / Q000378:metabolism*; D000067779:ELAV-Like Protein 4; D004622:Embryo, Mammalian / Q000033:anatomy & histology / Q000502:physiology; D058851:GPI-Linked Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D051379:Mice; D009046:Motor Neurons / Q000166:cytology / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism; D009479:Neuropeptides / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D055533:Survival of Motor Neuron 1 Protein / Q000235:genetics / Q000378:metabolism*; D015027:Zebrafish / Q000196:embryology / Q000502:physiology
chemical_list: D051959:ELAV Proteins; D000067779:ELAV-Like Protein 4; C498011:Elavl4 protein, mouse; D058851:GPI-Linked Proteins; C484539:NRN1 protein, human; D009419:Nerve Tissue Proteins; D009479:Neuropeptides; C484377:Nrn1 protein, mouse; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; C526472:Smn1 protein, mouse; D055533:Survival of Motor Neuron 1 Protein