Abstract
The localisation of poly(A) RNA in plant cells containing either reticular (Allium cepa) or chromocentric (Lupinus luteus, Arabidopsis thaliana) nuclei was studied through in situ hybridisation. In both types of nuclei, the amount of poly(A) RNA was much greater in the nucleus than in the cytoplasm. In the nuclei, poly(A) RNA was present in structures resembling nuclear bodies. The molecular composition as well as the characteristic ultrastructure of the bodies containing poly(A) RNA demonstrated that they were Cajal bodies. We showed that some poly(A) RNAs in Cajal bodies code for proteins. However, examination of the localisation of active RNA polymerase II and in situ run-on transcription assays both demonstrated that CBs are not sites of transcription and that BrU-containing RNA accumulates in these structures long after synthesis. In addition, it was demonstrated that accumulation of poly(A) RNA occurs in the nuclei and CBs of hypoxia-treated cells. Our findings indicated that CBs may be involved in the later stages of poly(A) RNA metabolism, playing a role storage or retention.
Highlights
Cajal bodies (CBs) are multifunctional domains present within the nuclei of plant and animal cells
We have shown that in the cells of plant roots, a considerably larger amount of poly(A) RNA is present in the nucleus than in the cytoplasm (Figure 1)
In comparison with the cytoplasm, larger proportions of both protein-coding mRNA and the total pool of poly(A) RNA are localised in the nucleus in COS-7 cells as well [33]
Summary
Cajal bodies (CBs) are multifunctional domains present within the nuclei of plant and animal cells. CBs are associated with particular stages of snRNA biogenesis, such as transcription, those involving loud export factors, modifications and snRNP assembly [7]. After transport to the cytoplasm, snRNAs undergo 59-cap hypermethylation, and acquired Sm proteins are reimported into nuclei and into CBs to complete their maturation [2]. This process includes the assembly of snRNP-specific proteins and snRNA methylation and pseudouridylation by scaRNPs [10,11], in addition to the formation of a complex consisting of U4, U5, and U6 snRNPs referred to as tri-snRNP by SART3/p110 proteins [12,7]
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