scholarly journals The SMN Complex Is Associated with snRNPs throughout Their Cytoplasmic Assembly Pathway

2002 ◽  
Vol 22 (18) ◽  
pp. 6533-6541 ◽  
Author(s):  
Séverine Massenet ◽  
Livio Pellizzoni ◽  
Sergey Paushkin ◽  
Iain W. Mattaj ◽  
Gideon Dreyfuss
Keyword(s):  
Motor Neurons ◽  
Muscular Atrophy ◽  
Sm Proteins ◽  
Assembly Pathway ◽  
Smn Complex ◽  
Complex Functions ◽  
Survival Of Motor Neurons ◽  
The Common ◽  
Smn Protein ◽  
Cytoplasmic Assembly

ABSTRACT The common neurodegenerative disease spinal muscular atrophy is caused by reduced levels of the survival of motor neurons (SMN) protein. SMN associates with several proteins (Gemin2 to Gemin6) to form a large complex which is found both in the cytoplasm and in the nucleus. The SMN complex functions in the assembly and metabolism of several RNPs, including spliceosomal snRNPs. The snRNP core assembly takes place in the cytoplasm from Sm proteins and newly exported snRNAs. Here, we identify three distinct cytoplasmic SMN complexes, each representing a defined intermediate in the snRNP biogenesis pathway. We show that the SMN complex associates with newly exported snRNAs containing the nonphosphorylated form of the snRNA export factor PHAX. The second SMN complex identified contains assembled Sm cores and m3G-capped snRNAs. Finally, the SMN complex is associated with a preimport complex containing m3G-capped snRNP cores bound to the snRNP nuclear import mediator snurportin1. Thus, the SMN complex is associated with snRNPs during the entire process of their biogenesis in the cytoplasm and may have multiple functions throughout this process.

scholarly journals The Survival of Motor Neurons Protein Determines the Capacity for snRNP Assembly: Biochemical Deficiency in Spinal Muscular Atrophy

2005 ◽  
Vol 25 (13) ◽  
pp. 5543-5551 ◽  
Author(s):  
Lili Wan ◽  
Daniel J. Battle ◽  
Jeongsik Yong ◽  
Amelie K. Gubitz ◽  
Stephen J. Kolb ◽  
...  
Keyword(s):  
Spinal Muscular Atrophy ◽  
Motor Neurons ◽  
Muscular Atrophy ◽  
Protein Levels ◽  
Small Nuclear Ribonucleoprotein ◽  
Cell Extracts ◽  
Smn Complex ◽  
Survival Of Motor Neurons ◽  
Smn Protein ◽  
Nuclear Ribonucleoprotein

ABSTRACT Reduction of the survival of motor neurons (SMN) protein levels causes the motor neuron degenerative disease spinal muscular atrophy, the severity of which correlates with the extent of reduction in SMN. SMN, together with Gemins 2 to 7, forms a complex that functions in the assembly of small nuclear ribonucleoprotein particles (snRNPs). Complete depletion of the SMN complex from cell extracts abolishes snRNP assembly, the formation of heptameric Sm cores on snRNAs. However, what effect, if any, reduction of SMN protein levels, as occurs in spinal muscular atrophy patients, has on the capacity of cells to produce snRNPs is not known. To address this, we developed a sensitive and quantitative assay for snRNP assembly, the formation of high-salt- and heparin-resistant stable Sm cores, that is strictly dependent on the SMN complex. We show that the extent of Sm core assembly is directly proportional to the amount of SMN protein in cell extracts. Consistent with this, pulse-labeling experiments demonstrate a significant reduction in the rate of snRNP biogenesis in low-SMN cells. Furthermore, extracts of cells from spinal muscular atrophy patients have a lower capacity for snRNP assembly that corresponds directly to the reduced amount of SMN. Thus, SMN determines the capacity for snRNP biogenesis, and our findings provide evidence for a measurable deficiency in a biochemical activity in cells from patients with spinal muscular atrophy.

SMN complexes of nucleus and cytoplasm: A proteomic study for SMA therapy

2010 ◽  
Vol 1 (4) ◽  
Author(s):  
Heidi Fuller ◽  
Glenn Morris
Keyword(s):  
Motor Neurons ◽  
Muscular Atrophy ◽  
Ubiquitin Proteasome System ◽  
Neuromuscular Disorder ◽  
Nuclear Extracts ◽  
Smn Complex ◽  
Proteomic Study ◽  
Ubiquitin Proteasome ◽  
Survival Of Motor Neurons ◽  
Smn Protein

AbstractReduced levels of the survival of motor neurons protein (SMN), cause the inherited neuromuscular disorder, spinal muscular atrophy (SMA). The majority of therapeutic approaches to date have been focused on finding ways to increase expression of functional SMN protein, though stabilization of SMN protein may also be an important consideration. SMN interacts, directly or indirectly, stably or transiently, with a large number of other proteins, some of which contribute to SMN stability and may therefore be potential targets for SMA therapy. We recently characterized the nuclear SMN interactome using LC-MALDI-TOF/TOF analysis of anti-SMN pull-downs and identified myb-binding protein-1a (Mybbp1a) as a novel partner. In light of interest in cytoplasm-specific roles of the SMN complex, we have applied the same approach to characterise the cytoplasmic SMN interactome. We now show that SMN complexes from HeLa cytoplasmic extracts differ significantly from those found in nuclear extracts, with gemin5, importinbeta and annexin A2 easily detected only in the cytoplasmic extracts, whereas interaction of SMN with Mybbp1a appears to occur only in the nucleus. SMN is ubiquitinylated and we also found proteins of the ubiquitin-proteasome system associated with SMN in the cytoplasm.

Small nuclear RNAs and mRNAs: linking RNA processing and transport to spinal muscular atrophy

2013 ◽  
Vol 41 (4) ◽  
pp. 871-875 ◽  
Author(s):  
Judith Sleeman
Keyword(s):  
Spinal Muscular Atrophy ◽  
Motor Neurons ◽  
Muscular Atrophy ◽  
Early Stage ◽  
Cell Type Specificity ◽  
Sm Proteins ◽  
Spinal Motor Neurons ◽  
Survival Of Motor Neurons ◽  
Smn Protein ◽  
Multicellular Organisms

The splicing of pre-mRNA by the spliceosome is a characteristic feature of eukaryotic cells, dependent on a group of snRNPs (small nuclear ribonucleoproteins). These splicing snRNPs have a complex assembly pathway involving multiple steps that take place in different regions of the cell, which is reflected in their complex subcellular distribution. Vital to the assembly of splicing snRNPs is the protein SMN (survival of motor neurons). In multicellular organisms, SMN acts in the cytoplasm, together with its associated protein complex to assemble a heptameric ring of proteins called the Sm proteins as an early stage in splicing snRNP assembly. A deficiency of the SMN protein results in the inherited neurodegenerative condition SMA (spinal muscular atrophy), a leading cause of infant mortality specifically affecting spinal motor neurons. It has long been a puzzle how lowered levels of a protein required for a process as fundamental as splicing snRNP assembly can result in a condition with such a definite cell-type-specificity. The present review highlights recent research that points to wider roles in RNA metabolism for both SMN itself and the Sm proteins with which it is linked.

scholarly journals Gemin3

1999 ◽  
Vol 147 (6) ◽  
pp. 1181-1194 ◽  
Author(s):  
Bernard Charroux ◽  
Livio Pellizzoni ◽  
Robert A. Perkinson ◽  
Andrej Shevchenko ◽  
Matthias Mann ◽  
...  
Keyword(s):  
Motor Neurons ◽  
Muscular Atrophy ◽  
Critical Role ◽  
Interacting Protein ◽  
Dead Box ◽  
Core Proteins ◽  
Smn Complex ◽  
Survival Of Motor Neurons ◽  
Smn Gene ◽  
Smn Protein

The survival of motor neurons (SMN) gene is the disease gene of spinal muscular atrophy (SMA), a common motor neuron degenerative disease. The SMN protein is part of a complex containing several proteins, of which one, SIP1 (SMN interacting protein 1), has been characterized so far. The SMN complex is found in both the cytoplasm and in the nucleus, where it is concentrated in bodies called gems. In the cytoplasm, SMN and SIP1 interact with the Sm core proteins of spliceosomal small nuclear ribonucleoproteins (snRNPs), and they play a critical role in snRNP assembly. In the nucleus, SMN is required for pre-mRNA splicing, likely by serving in the regeneration of snRNPs. Here, we report the identification of another component of the SMN complex, a novel DEAD box putative RNA helicase, named Gemin3. Gemin3 interacts directly with SMN, as well as with SmB, SmD2, and SmD3. Immunolocalization studies using mAbs to Gemin3 show that it colocalizes with SMN in gems. Gemin3 binds SMN via its unique COOH-terminal domain, and SMN mutations found in some SMA patients strongly reduce this interaction. The presence of a DEAD box motif in Gemin3 suggests that it may provide the catalytic activity that plays a critical role in the function of the SMN complex on RNPs.

scholarly journals Lymphotropic Herpesvirus saimiri Uses the SMN Complex To Assemble Sm Cores on Its Small RNAs

2005 ◽  
Vol 25 (2) ◽  
pp. 602-611 ◽  
Author(s):  
Tracey J. Golembe ◽  
Jeongsik Yong ◽  
Daniel J. Battle ◽  
Wenqin Feng ◽  
Lili Wan ◽  
...  
Keyword(s):  
Motor Neurons ◽  
Small Rnas ◽  
Herpesvirus Saimiri ◽  
New World Monkeys ◽  
Infectious Agents ◽  
Sm Proteins ◽  
General Utility ◽  
Smn Complex ◽  
Survival Of Motor Neurons ◽  
Very High

ABSTRACT The lymphotropic Herpesvirus saimiri (HVS) causes acute leukemia, T-cell lymphoma, and death in New World monkeys. HVS encodes seven small RNAs (HSURs) of unknown function. The HSURs acquire host Sm proteins and assemble Sm cores similar to those found on the spliceosomal small nuclear RNPs (snRNPs). Here we show that, like host snRNPs, HSURs use the SMN (survival of motor neurons) complex to assemble Sm cores. The HSURs bind the SMN complex directly and with very high affinity, similar to or higher than that of host snRNAs, and can outcompete host snRNAs for SMN-dependent assembly into RNPs. These observations highlight the general utility of the SMN complex for RNP assembly and suggest that infectious agents that engage the SMN complex may burden SMN-dependent pathways, possibly leading to a deleterious reduction in available SMN complex for essential host functions.

scholarly journals SMN-independent Subunits of the SMN Complex

2007 ◽  
Vol 282 (38) ◽  
pp. 27953-27959 ◽  
Author(s):  
Daniel J. Battle ◽  
Mumtaz Kasim ◽  
Jin Wang ◽  
Gideon Dreyfuss
Keyword(s):  
Motor Neurons ◽  
Atp Hydrolysis ◽  
Muscular Atrophy ◽  
Small Nuclear Rna ◽  
Small Nuclear Ribonucleoprotein ◽  
Cell Extracts ◽  
Smn Complex ◽  
Small Nuclear Rnas ◽  
Survival Of Motor Neurons ◽  
Nuclear Ribonucleoprotein

The survival of motor neurons (SMN) complex is essential for the biogenesis of small nuclear ribonucleoprotein (snRNP) complexes in eukaryotic cells. Reduced levels of SMN cause the motor neuron degenerative disease, spinal muscular atrophy. We identify here stable subunits of the SMN complex that do not contain SMN. Sedimentation and immunoprecipitation experiments using cell extracts reveal at least three complexes composed of Gemin3, -4, and -5; Gemin6, -7, and unrip; and SMN with Gemin2, as well as free Gemin5. Complexes containing Gemin3-Gemin4-Gemin5 and Gemin6-Gemin7-unrip persist at similar levels when SMN is reduced. In cells, immunofluorescence microscopy shows differential localization of Gemin5 after cell stress. We further show that the Gemin5-containing subunits bind small nuclear RNA independently of the SMN complex and without a requirement for exogenous ATP. ATP hydrolysis is, however, required for displacement of small nuclear RNAs from the Gemin5-containing subunits and their assembly into snRNPs. These findings demonstrate a modular nature of the SMN complex and identify a new intermediate in the snRNP assembly process.

scholarly journals Composition of the Survival Motor Neuron (SMN) complex in Drosophila melanogaster

2018 ◽  
Author(s):  
A. Gregory Matera ◽  
Amanda C. Raimer ◽  
Casey A. Schmidt ◽  
Jo A. Kelly ◽  
Gaith N. Droby ◽  
...  
Keyword(s):  
Drosophila Melanogaster ◽  
Motor Neuron ◽  
Muscular Atrophy ◽  
Structural Similarity ◽  
Survival Motor Neuron ◽  
Sm Proteins ◽  
Native Promoter ◽  
Smn Complex ◽  
Biological Studies ◽  
Smn Protein

AbstractSpinal Muscular Atrophy (SMA) is caused by homozygous mutations in the human survival motor neuron 1 (SMN1) gene. SMN protein has a well-characterized role in the biogenesis of small nuclear ribonucleoproteins (snRNPs), core components of the spliceosome. SMN is part of an oligomeric complex with core binding partners, collectively called Gemins. Biochemical and cell biological studies demonstrate that certain Gemins are required for proper snRNP assembly and transport. However, the precise functions of most Gemins are unknown. To gain a deeper understanding of the SMN complex in the context of metazoan evolution, we investigated the composition of the SMN complex in Drosophila melanogaster. Using a stable transgenic line that exclusively expresses Flag-tagged SMN from its native promoter, we previously found that Gemin2, Gemin3, Gemin5, and all nine classical Sm proteins, including Lsm10 and Lsm11, co-purify with SMN. Here, we show that CG2941 is also highly enriched in the pulldown. Reciprocal co-immunoprecipitation reveals that epitope-tagged CG2941 interacts with endogenous SMN in Schneider2 cells. Bioinformatic comparisons show that CG2941 shares sequence and structural similarity with metazoan Gemin4. Additional analysis shows that three other genes (CG14164, CG31950 and CG2371) are not orthologous to Gemins 6-7-8, respectively, as previously suggested. In D.melanogaster, CG2941 is located within an evolutionarily recent genomic triplication with two other nearly identical paralogous genes (CG32783 and CG32786). RNAi-mediated knockdown of CG2941 and its two close paralogs reveals that Gemin4 is essential for organismal viability.

scholarly journals A subset of SMN complex members have a specific role in tissue regeneration via ERBB pathway-mediated proliferation

2019 ◽  
Author(s):  
Wuhong Pei ◽  
Lisha Xu ◽  
Zelin Chen ◽  
Claire C Slevin ◽  
Kade P Pettie ◽  
...  
Keyword(s):  
Motor Neurons ◽  
Tissue Regeneration ◽  
Hair Cells ◽  
Muscular Atrophy ◽  
Essential Gene ◽  
Genetic Diseases ◽  
Rna Seq ◽  
Genetic Pathways ◽  
Smn Complex ◽  
Survival Of Motor Neurons

AbstractSpinal Muscular Atrophy (SMA) is the most common genetic disease in childhood. SMA is generally caused by mutations in SMN1. The Survival of Motor Neurons (SMN) complex consists of SMN1, Gemins (2–8) and Strap/Unrip. We previously demonstrated smn1 and gemin5 inhibited tissue regeneration in zebrafish. Here we investigated each individual SMN complex member and identified gemin3 as another regeneration-essential gene. These three genes are likely pan-regenerative since they affect the regeneration of hair cells, liver and caudal fin. RNA-Seq and miRNA-Seq analyses reveal that smn1, gemin3, and gemin5 are linked to a common set of genetic pathways, including the tp53 and ErbB pathways. Additional studies indicated all three genes facilitate regeneration by inhibiting the ErbB pathway, thereby allowing cell proliferation in the injured neuromasts. This study provides a new understanding of the SMN complex and a potential etiology for SMA and potentially other rare unidentified genetic diseases with similar symptoms.

scholarly journals Gemin4

2000 ◽  
Vol 148 (6) ◽  
pp. 1177-1186 ◽  
Author(s):  
Bernard Charroux ◽  
Livio Pellizzoni ◽  
Robert A. Perkinson ◽  
Jeongsik Yong ◽  
Andrej Shevchenko ◽  
...  
Keyword(s):  
Motor Neurons ◽  
Muscular Atrophy ◽  
Critical Role ◽  
Direct Interaction ◽  
Nuclear Bodies ◽  
Dead Box ◽  
Core Proteins ◽  
Smn Complex ◽  
Smn Protein

The survival of motor neurons (SMN) protein, the product of the neurodegenerative disease spinal muscular atrophy (SMA) gene, is localized both in the cytoplasm and in discrete nuclear bodies called gems. In both compartments SMN is part of a large complex that contains several proteins including Gemin2 (formerly SIP1) and the DEAD box protein Gemin3. In the cytoplasm, the SMN complex is associated with snRNP Sm core proteins and plays a critical role in spliceosomal snRNP assembly. In the nucleus, SMN is required for pre-mRNA splicing by serving in the regeneration of spliceosomes. These functions are likely impaired in cells of SMA patients because they have reduced levels of functional SMN. Here, we report the identification by nanoelectrospray mass spectrometry of a novel component of the SMN complex that we name Gemin4. Gemin4 is associated in vivo with the SMN complex through a direct interaction with Gemin3. The tight interaction of Gemin4 with Gemin3 suggests that it could serve as a cofactor of this DEAD box protein. Gemin4 also interacts directly with several of the Sm core proteins. Monoclonal antibodies against Gemin4 efficiently immunoprecipitate the spliceosomal U snRNAs U1 and U5 from Xenopus oocytes cytoplasm. Immunolocalization experiments show that Gemin4 is colocalized with SMN in the cytoplasm and in gems. Interestingly, Gemin4 is also detected in the nucleoli, suggesting that the SMN complex may also function in preribosomal RNA processing or ribosome assembly.

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