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Small Cajal body-specific RNAs of Drosophila function in the absence of Cajal bodies.

ABSTRACT: During their biogenesis small nuclear RNAs (snRNAs) undergo multiple covalent modifications that require guide RNAs to direct methylase and pseudouridylase enzymes to the appropriate nucleotides. Because of their localization in the nuclear Cajal body (CB), these guide RNAs are known as small CB-specific RNAs (scaRNAs). Using a fluorescent primer extension technique, we mapped the modified nucleotides in Drosophila U1, U2, U4, and U5 snRNAs. By fluorescent in situ hybridization (FISH) we showed that seven Drosophila scaRNAs are concentrated in easily detectable CBs. We used two assays based on Xenopus oocyte nuclei to demonstrate that three of these Drosophila scaRNAs do, in fact, function as guide RNAs. In flies null for the CB marker protein coilin, CBs are absent and there are no localized FISH signals for the scaRNAs. Nevertheless, biochemical experiments show that scaRNAs are present at normal levels and snRNAs are properly modified. Our experiments demonstrate that several scaRNAs are concentrated as expected in the CBs of wild-type Drosophila, but they function equally well in the nucleoplasm of mutant flies that lack CBs. We propose that the snRNA modification machinery is not limited to CBs, but is dispersed throughout the nucleoplasm of cells in general.

SUBMITTER: Deryusheva S

PROVIDER: S-EPMC2793299 | biostudies-literature | 2009 Dec

REPOSITORIES: biostudies-literature

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Small Cajal body-specific RNAs of Drosophila function in the absence of Cajal bodies.

Deryusheva Svetlana S Gall Joseph G JG

Molecular biology of the cell 20091201 24

During their biogenesis small nuclear RNAs (snRNAs) undergo multiple covalent modifications that require guide RNAs to direct methylase and pseudouridylase enzymes to the appropriate nucleotides. Because of their localization in the nuclear Cajal body (CB), these guide RNAs are known as small CB-specific RNAs (scaRNAs). Using a fluorescent primer extension technique, we mapped the modified nucleotides in Drosophila U1, U2, U4, and U5 snRNAs. By fluorescent in situ hybridization (FISH) we showed ...[more]

PMID: 19846657

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Project description:BACKGROUND: Spinal muscular atrophy is caused by reduced levels of the survival of motor neurons (SMN) protein. SMN is found in large complexes with Sm proteins and at least eight other proteins, including seven "gemins". These complexes are involved in the assembly of snRNPs in the cytoplasm and their transport into the nucleus, but the precise roles of the individual protein components are largely unknown. RESULTS: We have investigated the subcellular distribution of gemins using novel antibodies against gemins 3-7, and existing mAbs against SMN, gemin2, unrip, fibrillarin and profilin II. Most gemins were equally distributed between nuclear and cytoplasmic fractions of HeLa cells, but gemin5 and unrip were more abundant in the cytoplasm. In a cytoplasmic extract obtained by mild disruption of HeLa cells, nearly all the SMN and gemins 2-4 were in large complexes, but most of the gemin5 sedimented separately with a lower S value. Most of the unrip sedimented with gemins 6 and 7 near the top of the sucrose density gradients, separate from both SMN and gemin5. Anti-SMN mAbs pulled down gemin5 from cytoplasmic extracts, but not from nuclear extracts, and gemin5 did not co-sediment with large SMN complexes in nuclear extracts. These data suggest that gemin5 is easily detached from SMN-gemin complexes in the nucleus. By immuno-histochemistry, gemin5 was rarely detectable in nuclear gems/Cajal bodies, although it was accessible to antibody and easily detectable when present. This suggests that gemin5 is normally absent from SMN complexes in these nuclear storage sites. CONCLUSION: We conclude that SMN complexes usually exist without gemin5 in nuclear gems/Cajal bodies. Gemin5 is believed to be involved in capturing snRNA into SMN complexes in the cytoplasm for transport into the nucleus. We hypothesize that gemin5, though present in the nucleus, is no longer needed for SMN complex function during the time these complexes are stored in gems/Cajal bodies.

Project description:Small nucleolar RNAs (snoRNAs) and small Cajal body-specific RNAs (scaRNAs) are non-coding RNAs involved in the maturation of other RNA molecules and generally located in the introns of host genes. It is now emerging that altered sno/scaRNAs expression may play a pathological role in cancer. This study elucidates the patterns of sno/scaRNAs expression in multiple myeloma (MM), by profiling puri?ed malignant plasma cells from 55 MMs, 8 secondary plasma cell leukemias (sPCL) and 4 normal controls. Overall, a global sno/scaRNAs down-regulation was found in MMs and at more extent in sPCLs compared to normal plasma cells. Whereas SCARNA22 resulted the only sno/scaRNA characterizing the TC4 MM, TC2 group displayed a distinct sno/scaRNA signature overexpressing members of SNORD115 and SNORD116 families located in a region finely regulated by imprinting mechanism at 15q11. However, the imprinting center resulted overall hypomethylated in MMs independently of the SNORD115 and SNORD116 expression levels. Finally, integrative analyses with available gene expression and genome-wide data revealed the occurrence of significant sno/scaRNAs/host genes co-expression and the putative influence of allelic imbalances on specific snoRNAs expression. Our data extend the current view of sno/scaRNAs deregulation in cancer and add novel information into the bio-molecular complexity of plasma cell dyscrasias. This series of microarray experiments contains the gene expression profiles of purified plasma cells (PCs) obtained from 55 multiple myeloma (MM) and 8 secondary plasma cell leukemia (sPCL) at diagnosis. PCs were purified from bone marrow samples using CD138 immunomagnetic microbeads according to the manufacturer's instructions (MidiMACS system, Miltenyi Biotec); the purity of the positively selected PCs was assessed by morphology and flow cytometry and was > 90% in all cases. 5.5 micrograms of single-stranded DNA target obtained from 100 ng of purified total RNA was fragmented and then labeled using the WT Terminal Labeling Kit according to the standard Affymetrix protocol (GeneChipÂ® Whole Transcript (WT) Sense Target Labeling Assay Manual). The fragmented labeled single-stranded DNA target was hybridized for 16 hours and 30 minutes at 45Â°C on GeneChipÂ® Gene 1.0 ST array according to the standard Affymetrix protocol. Washing and scanning were performed using GeneChip System of Affymetrix (GeneChip Hybridization Oven 640, GeneChip Fluidics Station 450 and GeneChip Scanner 7G). The raw intensity expression values were processed by Robust Multi-array Average (RMA) complete procedure with the re-mapped Chip Definition Files (CDF) from BrainArray libraries version 15.0.0 available at http://brainarray.mbni.med.umich.edu/Brainarray/Database/CustomCDF/15.0.0/entrezg.asp.

Dataset Information

Small Cajal body-specific RNAs of Drosophila function in the absence of Cajal bodies.

Publications

Small Cajal body-specific RNAs of Drosophila function in the absence of Cajal bodies.

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