Molecular analysis of the coiled body

Abstract

There is increasing interest in studying how specific metabolic activities within the nucleus are organised into functional domains. The best known example is the nucleolus where rRNA genes are transcribed and rRNA processed and assembled into ribosomal subunits. Other subnuclear domains have been known for many years through morphological studies but are only recently being analysed at the molecular level. Here we focus on an evolutionarily conserved nuclear domain, called the coiled body, which contains splicing snRNPs. We review recent literature on the coiled body and discuss a possible model for its biological function.

The Movement of Coiled Bodies Visualized in Living Plant Cells by the Green Fluorescent Protein

“…It has been suggested that coiled bodies are assembled at the nucleolar periphery (Bohmann et al, 1995), and coiled bodies are often found adjacent to nucleoli or physically attached to nucleoli, as though in the process of emergence or fusion (Lafarga et al, 1983;Ferreira and Carmo-Fonseca, 1995;Matera, 1998). In most BY-2 cells, we observed very small coiled bodies inside the nucleolus, which were either too small or photobleached too quickly to follow during time-lapse experiments.…”

Coilin Can Form a Complex with the U7 Small Nuclear Ribonucleoprotein

“…Coilin itself is rapidly targeted to CBs in the oocyte and in transfected tissue culture cells (Bohmann et al, 1995), suggesting that it might be the specific carrier protein. The relatively weak interaction between coilin and the U7 snRNP is consistent with a transitory role in which coilin would bind to the U7 snRNP, travel with it to the CB, and release it there.…”

“…The nuclear protein coilin is most highly concentrated in CBs, which also contain a variety of snRNPs involved in splicing, pre-rRNA processing, and histone pre-mRNA 3Ј-end processing (reviewed by Lamond and Carmo-Fonseca, 1993;Bohmann et al, 1995;Roth, 1995;Lamond and Earnshaw, 1998;Matera, 1998). The precise spatial relationship between coilin and other components is not resolvable in the small CBs of tissue culture and somatic nuclei but is evident in the much larger CBs (spheres) of the Xenopus GV.…”

“…They are characterized by the presence of a unique protein, p80-coilin , along with components involved in three different RNA-processing pathways: splicing, prerRNA processing, and histone pre-mRNA processing (reviewed by Lamond and Carmo-Fonseca, 1993;Bohmann et al, 1995;Gall et al, 1995;Roth, 1995;Lamond and Earnshaw, 1998;Matera, 1998). Long before their homology to somatic CBs was recognized, CBs had been described from the oocyte nucleus or germinal vesicle (GV) of insects (Jö rgensen, 1913) and amphibians (Gall, 1954;Callan and Lloyd, 1960).…”

Localization of hepatitis delta virus RNA in the nucleus of human cells

“…Based on the data obtained by transient expression of each form of the delta antigen in the absence of viral genome replication, we conclude that dAg-S on its own has the ability to assemble into focal aggregates+ Due to its tight interaction with HDV RNA and dAg-L, dAg-S could therefore be responsible for the appearance of the delta foci+ Because HDV depends on HBV to supply the envelope proteins required for completion of packaging, secretion, and infection (see Monjardino & Lai, 1993), mammalian cell systems such as Huh7-D12, which are solely transfected with HDV cDNA, fail to export viral particles to the cytoplasm+ Thus, the foci may represent depository sites for delta RNA and antigens trapped within the nucleus+ In this regard, we are currently analyzing the distribution of HDV components in cells that express HBV envelope proteins+ At present, it is well known that the nucleus contains discrete subdomains that appear as foci or speckles when viewed with the fluorescence microscope+ These include different types of nuclear bodies (for review, see Spector, 1993;Bohmann et al+, 1995), and we show here that the delta foci are occasionally seen in their close vicinity+ However, more than 50% of delta foci are independent from either coiled bodies or PML bodies+ In contrast, the delta foci are consistently adjacent to so-called nuclear speckles or clusters of interchromatin granules, which are highly enriched in components of the splicing machinery (Spector, 1993)+ Although it was initially proposed that nuclear speckles represent preferential splicing sites in the nucleus, subsequent experiments questioned this view+ In particular, there are now several lines of evidence indicating that splicing occurs co-transcriptionally and that nascent RNA transcripts are localized at many sites in the nucleus other than clusters of interchromatin granules (reviewed in FIGURE 8. Intranuclear distribution of ADAR1 in Huh7 and Huh7-D12 cells+ A: Huh7 cells labeled with affinity-purified anti-ADAR1 antibodies show a diffuse staining of the nucleoplasm+ B,C: Huh7-D12 cells were double-labeled with anti-ADAR1 affinity-purified rabbit antibodies (B) and a monoclonal antibody anti-p24 (C)+ Bar, 10 mm+ Fakan, 1994;Spector, 1996;Singer & Green, 1997)+ In addition to splicing factors, RNA polymerase II is also detected in clusters of interchromatin granules (see Zeng et al+, 1997 and references therein), and it is now believed that these molecules shuttle between the clusters of interchromatin granules and the sites of active RNA synthesis depending upon transcriptional activity (Misteli et al+, 1997)+ This suggests that the speckles may represent a storage compartment for inactive transcription and splicing factors (Spector, 1993(Spector, , 1996+ Alternatively, it has been proposed that transcription and splicing factors localize to clusters of interchromatin granules for some form of recycling or reactivation between rounds of pre-mRNA synthesis (Bohmann et al+, 1995;Zeng et al+, 1997)+ Experiments using oligo(dT) probes revealed that clusters of interchromatin granules contain polyadenylated RNA (Cart...…”