Pre-mRNA splicing is a critical step in eukaryotic gene expression that contributes to proteomic, cellular and developmental complexity. Small nuclear (sn)RNAs are core spliceosomal components, however, the extent to which differential expression of snRNA isoforms regulates splicing is completely unknown. This is partly due to difficulties in the accurate analysis of the spatial and temporal expression patterns of snRNAs.
Here, researchers at the University of North Carolina, Chapel Hill use high throughput RNA-sequencing (RNA-seq) data to profile expression of four major snRNAs throughout Drosophila development. This analysis shows that individual isoforms of each snRNA have distinct expression patterns in the embryo, larva and pharate adult stages. Expression of these isoforms is more heterogeneous during embryogenesis, and as development progresses, a single isoform from each snRNA subtype gradually dominates expression. Despite the lack of stable snRNA orthologous groups during evolution, this developmental switching of snRNA isoforms also occurs in distantly related vertebrate species, such as Xenopus, mouse and human. These results indicate that expression of snRNA isoforms is regulated, and lay the foundation for functional studies of individual snRNA isoforms.