QNQKE targeting motif for the SMN-Gemin multiprotein complexin neurons

Department of Cell Biology, Emory University, Atlanta, Georgia, United States
Journal of Neuroscience Research (Impact Factor: 2.59). 09/2007; 85(12):2657-67. DOI: 10.1002/jnr.21308
Source: PubMed


Spinal muscular atrophy (SMA) is a heritable neurodegenerative disease affecting motor neurons that is caused by the impaired expression of the full-length form of the survival of motor neuron protein (SMN), which may have a specialized function in neurons related to mRNA localization. We have previously shown that a population SMN complexes contain Gemin ribonucleoproteins and traffic in the form of granules to neuronal processes and growth cones of cultured neurons. A QNQKE sequence within exon 7 has been shown to be necessary for both cytoplasmic localization of SMN and axonal function. Here we show that the QNQKE sequence can influence the nucleocytoplasmic distribution of the SMN-Gemin complex and its localization into neuronal processes. QNQKE exerted a stronger effect on SMN localization in primary neurons compared with COS-7 cells. By using double-label fluorescence in situ hybridization and immunofluorescence, SMN granules within neuronal processes colocalized with poly-(A) mRNA and PABP. These findings provide further evidence in support of a neuronal function for SMN and motivation to investigate for impaired assembly and/or localization of mRNP complexes as an underlying cause of SMA.

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Available from: Gary Bassell, Aug 04, 2014
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    • "Gemin2 tightly associates with SMN to form the cytoplasmic SMN complex to mediate snRNP assembly [12], [13]. Syncrip and Pabp-C1 are associated with Smn granules and have been suggested to be involved in axonal mRNA transport [19], [28], [29]. Only Cop-α, but not Pabp-C1, Gemin2, or Syncrip, had a similar staining pattern to mSmn, suggesting that Cop-α, a protein involved in coating vesicles during secretion from the Golgi apparatus, may be involved in mSmn granule secretion. "
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    ABSTRACT: Proximal spinal muscular atrophy (SMA) is a neurodegenerative disorder caused by deficiency of the ubiquitous Survival of Motor Neuron (SMN) protein. SMN has been shown to be transported in granules along the axon and moved through cytoskeletal elements. However, the role and nature of SMN granules are still not well characterized. Here, using immunocytochemical methods and time-lapse studies we show that SMN granules colocalize with the Golgi apparatus in motor neuron-like NSC34 cells. Electron microscopy clearly revealed that SMN granules are transported into the Golgi stack and aggregate in the trans-Golgi apparatus. SMN granules are characterized as either coated or un-coated and behave like regulated secretory granules. Treatment of cells with monensin to disrupt Golgi-mediated granule secretion decreased SMN expression in neurites and caused growth cone defects similar to those seen in SMN knockdown cells. Knockdown of Cop-α, the protein that coats vesicles transporting proteins between the Golgi compartments, caused SMN granule accumulation in the Golgi apparatus. In addition to the well-studied role of SMN in small nuclear ribonucleoprotein (SnRNP) assembly, this work links SMN granules with the Golgi network and thus sheds light on Golgi-mediated SMN granule transport.
    Full-text · Article · Dec 2012 · PLoS ONE
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    • "Hsp70: RFP-hSMN construct—The RFP-hSMN (Zhang et al., 2007) in pCS2 was digested with Bam HI and Not I and cloned into pBluescript vector that contained 2 SceI sites (RFP-hSMN/pBluescripSceI plasmid). The 1.5 kb heat shock 70 promoter (hsp70) was released from the pHSP70/4 EGFP-1 plasmid (Halloran et al., 2000) using the Bam HI site and cloned into the RFP-hSMN/pBluescript plasmid containing I-SceI sites to enhance transgenesis (Thermes et al., 2002). "
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    ABSTRACT: The actin-binding protein plastin 3 (PLS3) has been identified as a modifier of the human motoneuron disease spinal muscular atrophy (SMA). SMA is caused by decreased levels of the survival motor neuron protein (SMN) and in its most severe form causes death in infants and young children. To understand the mechanism of PLS3 in SMA, we have analyzed pls3 RNA and protein in zebrafish smn mutants. We show that Pls3 protein levels are severely decreased in smn(-/-) mutants without a reduction in pls3 mRNA levels. Moreover, we show that both pls3 mRNA and protein stability are unaffected when Smn is reduced. This indicates that SMN affects PLS3 protein production. We had previously shown that, in smn mutants, the presynaptic protein SV2 is decreased at neuromuscular junctions. Transgenically driving human PLS3 in motoneurons rescues the decrease in SV2 expression. To determine whether PLS3 could also rescue function, we performed behavioral analysis on smn mutants and found that they had a significant decrease in spontaneous swimming and turning. Driving PLS3 transgenically in motoneurons rescued both of these defects. These data show that PLS3 protein levels are dependent on SMN and that PLS3 is able to rescue the neuromuscular defects and corresponding movement phenotypes caused by low levels of Smn suggesting that decreased PLS3 contributes to SMA motor phenotypes.
    Preview · Article · Apr 2012 · The Journal of Neuroscience : The Official Journal of the Society for Neuroscience
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    ABSTRACT: Spinal muscular atrophy (SMA) is an autosomal recessive neurodegenerative disease. Loss of the survival motor neuron (SMN1) gene, in the presence of the SMN2 gene causes SMA. SMN functions in snRNP assembly in all cell types, however, it is unclear how this function results in specifically motor neuron cell death. Lack of endogenous mouse SMN (Smn) in mice results in embryonic lethality. Introduction of two copies of human SMN2 results in a mouse with severe SMA, while one copy of SMN2 is insufficient to overcome embryonic lethality. We show that SMN(A111G), an allele capable of snRNP assembly, can rescue mice that lack Smn and contain either one or two copies of SMN2 (SMA mice). The correction of SMA in these animals was directly correlated with snRNP assembly activity in spinal cord, as was correction of snRNA levels. These data support snRNP assembly as being the critical function affected in SMA and suggests that the levels of snRNPs are critical to motor neurons. Furthermore, SMN(A111G) cannot rescue Smn-/- mice without SMN2 suggesting that both SMN(A111G) and SMN from SMN2 undergo intragenic complementation in vivo to function in heteromeric complexes that have greater function than either allele alone. The oligomer composed of limiting full-length SMN and SMN(A111G) has substantial snRNP assembly activity. Also, the SMN(A2G) and SMN(A111G) alleles in vivo did not complement each other leading to the possibility that these mutations could affect the same function.
    Full-text · Article · Apr 2009 · Human Molecular Genetics
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