Splicing of precursor mRNAs is an important cellular process that removes non-coding and, occasionally, coding regions from DNA transcripts and allows the generation of different protein products from the same gene. Splicing is catalysed by the spliceosome, a large ribonucleoprotein complex assembled from small nuclear ribonucleoproteins (snRNPs), which contain Sm proteins and uridine-rich small nuclear RNAs (snRNAs). snRNP biogenesis involves nuclear snRNP processing in Cajal bodies. Now, Carlos Suñé and co-workers (Moreno-Castro et al., 2019) investigate how the splicing factor TCERG1 contributes to Cajal body integrity. They find that the accumulation of the Cajal body proteins coilin and NOLC1 into nuclear speckles is reduced upon TCERG1 knockdown, suggesting that Cajal bodies are disrupted. However, other nuclear structures, such as gems and the histone locus body, remain intact in the absence of TCERG1. By analysing the localisation of TCERG1, the authors demonstrate that it partially colocalises with coilin. Moreover, TCERG1 binds to coilin and other components of Cajal bodies, indicating that TCERG1 itself associates with these structures. The authors also reveal that the association of the Sm proteins with snRNAs is reduced upon TCERG1 knockdown. Collectively, these findings suggest that TCERG1 is a novel factor that is required for the integrity of Cajal bodies and the biogenesis of snRNPs that form part of the spliceosome.
