The role of coilin in snRNP quality control

Mammalian genes are transcribed as precursors - pre-mRNA. They contain coding sequences (exons) and non-coding sequences (introns). Splicing, a process of cutting out introns and joining exons to generate mature mRNA, is carried out by a spliceosome. The spliceosome consists of five small nuclear ribonucleoprotein (snRNP) particles and numerous associated proteins. Its assembly is a complex process involving a specific nuclear sub-compartment, the Cajal body (CB). Here, we investigate function of the CB scaffold protein, coilin, in snRNP quality control in HeLa cells. Sequestration of immature snRNP in coilin-deficient cells is analysed by fluorescence in situ hybridisation. We show that without coilin the cells are unable to sequester them. Next, we provide evidence that absence of coilin does not sensitise HeLa cells for perturbation in snRNP maturation in terms of cell proliferation. Moreover, coilin deficiency does not result in significant changes in U4, U5 or U6 snRNA steady state levels. Therefore, coilin, and, in this way, Cajal bodies do not become essential under the conditions of strained snRNP biogenesis