Cross-Talk between Snurportin1 Subdomains

Ospina, Jason K.; Gonsalvez, Graydon B.; Bednenko, Janna; Darżynkiewicz, Edward; Gerace, Larry; Matera, A. Gregory

doi:10.1091/mbc.e05-04-0316

Cited by 30 publications

(35 citation statements)

References 63 publications

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“…The results demonstrated that import of SMN and splicing snRNPs are coupled in somatic cells. 62,65 Two lines of evidence substantiated this conclusion. First, purified SMN complex was required for in vitro snRNP import and vice versa.…”

Section: Smn and Cytoplasmic Snrnp Assemblymentioning

confidence: 87%

“…In any event, the adaptor for the TMG cap is called snurportin1 (SPN1); this protein binds directly to the TMG cap and significantly improves the kinetics of snRNP import. 61,64,65 At the time, relatively little was known about the factor that mediates the interaction between the Sm core and importin b. Previous studies had indicated that the Sm core adaptor is a cytosolic factor that binds to Sm proteins and importin b.…”

Section: Smn and Cytoplasmic Snrnp Assemblymentioning

confidence: 99%

“…The precise composition of the Gemin proteins and the overall stoichiometry of importin b within this complex is completely unknown. Given the independence of the 2 import pathways in vitro, 61,62,65 the question remains whether the Smcore and TMG cap import adaptors act synergistically in vivo. Moreover, the SMN complex might only play a role in import of newly-assembled snRNPs.…”

Section: Smn Import Regulationmentioning

confidence: 99%

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SMN - A chaperone for nuclear RNP social occasions?

2016

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Survival Motor Neuron (SMN) protein localizes to both the nucleus and the cytoplasm. Cytoplasmic SMN is diffusely localized in large oligomeric complexes with core member proteins, called Gemins. Biochemical and cell biological studies have demonstrated that the SMN complex is required for the cytoplasmic assembly and nuclear transport of Sm-class ribonucleoproteins (RNPs). Nuclear SMN accumulates with spliceosomal small nuclear (sn)RNPs in Cajal bodies, sub-domains involved in multiple facets of snRNP maturation. Thus, the SMN complex forms stable associations with both nuclear and cytoplasmic snRNPs, and plays a critical role in their biogenesis. In this review, we focus on potential functions of the nuclear SMN complex, with particular emphasis on its role within the Cajal body.

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Section: Smn and Cytoplasmic Snrnp Assemblymentioning

confidence: 87%

Section: Smn and Cytoplasmic Snrnp Assemblymentioning

confidence: 99%

Section: Smn Import Regulationmentioning

confidence: 99%

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SMN - A chaperone for nuclear RNP social occasions?

2016

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“…Notably, U1 snRNP did not rescue the coilin morphant phenotype. U1 is the least well-concentrated snRNA in CBs, and mature U1 snRNP does not target to CBs in nuclear transport reactions, whereas U2 snRNP does 12,42 . Similarly to the tri-snRNP, intermediates in mature U2 snRNP formation can be trapped in CBs upon knockdown of appropriate assembly factors 17 .…”

Section: Discussionmentioning

confidence: 99%

Coilin-dependent snRNP assembly is essential for zebrafish embryogenesis

Strzelecka

Trowitzsch

Weber

et al. 2010

Nat Struct Mol Biol

147

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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“…7B). Since, during interphase the presence of CRM1 in CB is well established, 27,28,42 CRM1 could already be in the CB in early G1a and b (Fig. 7B).…”

mentioning

confidence: 82%

The traffic of proteins between nucleolar organizer regions and prenucleolar bodies governs the assembly of the nucleolus at exit of mitosis

Muro¹,

Gébrane-Younès²,

Jobart-Malfait³

et al. 2010

Nucleus

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is also a plurifunctional domain involved in assembly of RNPs and a target for viral proteins and viral RNAs. [8][9][10][11] The assembly of the nucleolus starts during telophase by activation of rDNA transcription of several nucleolar organizer regions (NORs) and by progressive recruitment of early and late processing proteins on rRNA transcripts. In parallel, prenucleolar bodies (PNBs) are assembled. [12][13][14][15][16] The PNBs contain nucleolar processing proteins, pre-rRNAs and snoRNAs. 17 Even though PNBs are formed in all animal and plant cells, their role in the dynamics of DFC and GC assembly is still unknown.It is possible to observe and measure the motion of proteins or RNP complexes in living cells. Using these approaches it was demonstrated that macromolecules within the nucleus are highly mobile by a combination of passive diffusion and highaffinity binding sites. [18][19][20] It was also established that the assembly of nuclear bodies after mitosis is strictly ordered. 14,[21][22][23][24] It is now important to characterize the dynamics of the complexes during the building of the functional domains integrated in the nuclear network. We examined the role of the PNB step in the kinetics of DFC and GC assembly. Using photoactivation, 25 weThe building of nuclear bodies after mitosis is a coordinated event crucial for nuclear organization and function. The nucleolus is assembled during early G 1 phase. Here, two periods (early G1a and early G1b) have been defined. During these periods, the nucleolar compartments (DFC, GC) corresponding to different steps of ribosome biogenesis are progressively assembled. In telophase, rDNA transcription is first activated and PNBs (reservoirs of nucleolar processing proteins) are formed. The traffic of the processing proteins between incipient nucleoli and PNBs was analyzed using photoactivation. We demonstrate that the DFC protein fibrillarin passes from one incipient nucleolus to other nucleoli but not to PNBs, and that the GC proteins, B23/NPM and Nop52, shuttle between PNBs and incipient nucleoli. This difference in traffic suggests a way of regulating assembly first of DFC and then of GC. The time of residency of GC proteins is high in incipient nucleoli compared to interphase nuclei, it decreases in LMB-treated early G1a cells impairing the assembly of GC. Because the assembly of the nucleolus and that of the Cajal body at the exit from mitosis are both sensitive to CRM1 activity, we discuss the fact that assembly of GC and/or its interaction with DFC in early G1a depends on shuttling between PNBs and NORs in a manner dependent on Cajal body assembly.www.landesbioscience.comNucleus 203 RESEARCH PAPER decreases as expected of proteins trafficking between nucleolus and nucleoplasm. Surprisingly, activated PAGFP-B23/NPM is detected in PNBs 5-10 seconds after activation (Fig. 1D). The uptake of B23/NPM in PNBs is observed in all PNBs containing mDsRed-Nop52 visible in the focal plane. This indicates that feedback of activated molecules occurs between incipient nuc...

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Cross-Talk between Snurportin1 Subdomains

Cited by 30 publications

References 63 publications

SMN - A chaperone for nuclear RNP social occasions?

SMN - A chaperone for nuclear RNP social occasions?

Coilin-dependent snRNP assembly is essential for zebrafish embryogenesis

The traffic of proteins between nucleolar organizer regions and prenucleolar bodies governs the assembly of the nucleolus at exit of mitosis

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