Reduced U snRNP assembly causes motor axon degeneration in an animal model for spinal muscular atrophy

Winkler, Christoph; Eggert, Christian; Gradl, Dietmar; Meister, Gunter; Giegerich, Marieke; Wedlich, Doris; Laggerbauer, Bernhard; Fischer, Utz

doi:10.1101/gad.342005

Cited by 210 publications

(202 citation statements)

References 45 publications

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“…8). These data indicate that purified human snRNPs are catalytically active in zebrafish embryos, consistent with a prior study 34 . Moreover, rescue of mRNA levels by human snRNPs confirms that the mRNA-loss in coilin morphants was caused specifically by the snRNP deficit.…”

Section: Mature Human Spliceosomal Snrnps Rescue the Coilin Morphantsupporting

confidence: 91%

Coilin-dependent snRNP assembly is essential for zebrafish embryogenesis

Strzelecka

Trowitzsch

Weber

et al. 2010

Nat Struct Mol Biol

153

164

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0 3 a r t i c l e sIn eukaryotes, organelles delimited by lipid bilayers support the organization of cellular functions, as exemplified by the segregation of chromatin into the cell nucleus. However, many subcellular compartments-nucleoli, Cajal and PML bodies, polar granules, stress granules, P bodies and others-lack membranes. How these structures contribute to cellular physiology is largely unknown 1 . The Cajal body (CB) is a 0.5-to 1-µm nuclear compartment initially described by Ramon y Cajal in silver-stained sections of vertebrate cerebral cortex 2 . Because the CB is conserved in evolution and is uniquely marked by the protein coilin, it has served as a general model for subnuclear structure and function 1,2 . Numerous factors essential for pre-mRNA splicing, histone mRNA 3′-end processing, telomere maintenance and rRNA processing are concentrated in CBs. Yet CB components exchange rapidly with the nucleoplasm, where most of these processes occur 3 . The challenge, therefore, has been to identify the function of CBs.Despite the localization of splicing machinery in CBs, they are not the sites of pre-mRNA splicing 4,5 . Splicing occurs throughout the nucleus and is catalyzed by the spliceosome, a macromolecular complex formed on pre-mRNA from five essential snRNPs 6 . Each spliceosomal snRNP comprises a unique 100-to 200-nucleotide snRNA (U1, U2, U4, U5 and U6) that is post-transcriptionally modified and associated with a number of snRNP-specific proteins 6,7 . Several roles for CBs in spliceosomal snRNP biogenesis have been proposed based on the localization of specific steps in snRNP assembly in the CBs of cultured cell lines. After transcription and export to the cytoplasm, U1, U2, U4 and U5 snRNAs receive a heteroheptameric ring of Sm proteins assembled by the SMN complex; subsequently, their 5′ ends are hypermethylated 8 . The Sm ring and trimethylguanosine (TMG) cap are signals for snRNP reimport into the nucleus, where these still-immature core snRNPs first concentrate in CBs 9-12 . CBs contain scaRNAs, which then guide site-specific modification of the snRNAs 13 . Importantly, intermediates in the final snRNP maturation steps, reflecting RNA structural rearrangements and the recruitment of snRNP-specific proteins, are highly concentrated in CBs 14-17 . These observations have led to the proposal that CBs are the sites of snRNP assembly, but an essential role for CBs in this process has not been shown.The coilin protein may hold the key to CB function. Immunoelectron microscopy studies of CBs reveal thread-like, coilin-positive aggregates, suggesting that coilin is integral to CB structure 2 . Consistent with this, coilin resides longer in CBs than any other examined component in vivo 3,18 . Notably, depletion of coilin results in the dispersal of many CB components. Without coilin, spliceosomal factors become nucleoplasmic, and other classes of CB-localized factors (for example, SMN, fibrillarin and small Cajal body-specific RNAs (scaRNAs)) continue to self-associate in discrete 'residual bodies' ...

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Section: Mature Human Spliceosomal Snrnps Rescue the Coilin Morphantsupporting

confidence: 91%

Coilin-dependent snRNP assembly is essential for zebrafish embryogenesis

Strzelecka

Trowitzsch

Weber

et al. 2010

Nat Struct Mol Biol

153

164

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“…Nuclear SMN is critical in the assembly of many different classes of small ribonucleoprotein particles (snRNPs); thus, SMN has a housekeeping role in snRNP biogenesis and in pre-mR-NA splicing [9,10]. Although a decrease of snRNP biogenesis has been observed in vitro [11], its connection to pathological changes in spinal motor neurons in SMA is not understood. Recent studies reveal that, besides being located in the nucleus, SMN protein also accumulates in the dendrites and axons of neurons and is associated with microtubules [12,13].…”

Section: Introductionmentioning

confidence: 99%

Recapitulation of spinal motor neuron-specific disease phenotypes in a human cell model of spinal muscular atrophy

Wang

Zhang

2012

Cell Res

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Establishing human cell models of spinal muscular atrophy (SMA) to mimic motor neuron-specific phenotypes holds the key to understanding the pathogenesis of this devastating disease. Here, we developed a closely representative cell model of SMA by knocking down the disease-determining gene, survival motor neuron (SMN), in human embryonic stem cells (hESCs). Our study with this cell model demonstrated that knocking down of SMN does not interfere with neural induction or the initial specification of spinal motor neurons. Notably, the axonal outgrowth of spinal motor neurons was significantly impaired and these disease-mimicking neurons subsequently degenerated. Furthermore, these disease phenotypes were caused by SMN-full length (SMN-FL) but not SMN-∆7 (lacking exon 7) knockdown, and were specific to spinal motor neurons. Restoring the expression of SMN-FL completely ameliorated all of the disease phenotypes, including specific axonal defects and motor neuron loss. Finally, knockdown of SMN-FL led to excessive mitochondrial oxidative stress in human motor neuron progenitors. The involvement of oxidative stress in the degeneration of spinal motor neurons in the SMA cell model was further confirmed by the administration of N-acetylcysteine, a potent antioxidant, which prevented disease-related apoptosis and subsequent motor neuron death. Thus, we report here the successful establishment of an hESC-based SMA model, which exhibits disease gene isoform specificity, cell type specificity, and phenotype reversibility. Our model provides a unique paradigm for studying how motor neurons specifically degenerate and highlights the potential importance of antioxidants for the treatment of SMA.

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“…In addition to larval Smn mutants, our laboratory has previously reported SMA-like phenotypes in adult flies containing a hypomorphic Smn E33 mutation (Rajendra et al, 2007). Thus, although it is clear that perturbations in the SMN complex can indeed result in neuromuscular dysfunction, the contribution that snRNP biogenesis plays in the etiology of these phenotypes remains a subject of ongoing investigation (Shpargel and Matera, 2005;Wan et al, 2005;Winkler et al, 2005;Gabanella et al, 2007). Further complicating interpretation of the various SMA models is the fact that the SMN complex appears to function in tissue-specific pathways involved in both neuronal (McWhorter et al, 2003;Zhang et al, 2006;Bowerman et al, 2007) and muscular development (Shafey et al, 2005;Rajendra et al, 2007).…”

Section: Gemin3 Smn and Neuromuscular Functionmentioning

confidence: 99%

“…Depletion of Smn in zebrafish embryos by morpholino injection elicits defects in motor axon outgrowth, although the primary versus secondary nature of the reported Smn phenotypes is unclear and the results seem to depend on the extent of depletion (McWhorter et al, 2003;Winkler et al, 2005;Carrel et al, 2006;McWhorter et al, 2007). Interestingly, depletion of Gemin2 is reported to have conflicting effects on motor axon development, possibly because of differences in the levels of gene inhibition or in the methods of phenotypic analysis (Winkler et al, 2005;McWhorter et al, 2007).…”

Section: Gemin3 Smn and Neuromuscular Functionmentioning

confidence: 99%

Gemin3Is an Essential Gene Required for Larval Motor Function and Pupation inDrosophila

Shpargel

Praveen

Rajendra

et al. 2009

MBoC

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The assembly of metazoan Sm-class small nuclear ribonucleoproteins (snRNPs) is an elaborate, step-wise process that takes place in multiple subcellular compartments. The initial steps, including formation of the core RNP, are mediated by the survival motor neuron (SMN) protein complex. Loss-of-function mutations in human SMN1 result in a neuromuscular disease called spinal muscular atrophy. The SMN complex is comprised of SMN and a number of tightly associated proteins, collectively called Gemins. In this report, we identify and characterize the fruitfly ortholog of the DEAD box protein, Gemin3. Drosophila Gemin3 (dGem3) colocalizes and interacts with dSMN in vitro and in vivo. RNA interference for dGem3 codepletes dSMN and inhibits efficient Sm core assembly in vitro. Transposon insertion mutations in Gemin3 are larval lethals and also codeplete dSMN. Transgenic overexpression of dGem3 rescues lethality, but overexpression of dSMN does not, indicating that loss of dSMN is not the primary cause of death. Gemin3 mutant larvae exhibit motor defects similar to previously characterized Smn alleles. Remarkably, appreciable numbers of Gemin3 mutants (along with one previously undescribed Smn allele) survive as larvae for several weeks without pupating. Our results demonstrate the conservation of Gemin3 protein function in metazoan snRNP assembly and reveal that loss of either Smn or Gemin3 can contribute to neuromuscular dysfunction.

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Reduced U snRNP assembly causes motor axon degeneration in an animal model for spinal muscular atrophy

Cited by 210 publications

References 45 publications

Coilin-dependent snRNP assembly is essential for zebrafish embryogenesis

Coilin-dependent snRNP assembly is essential for zebrafish embryogenesis

Recapitulation of spinal motor neuron-specific disease phenotypes in a human cell model of spinal muscular atrophy

Gemin3Is an Essential Gene Required for Larval Motor Function and Pupation inDrosophila

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