Alternative splicing is essential for the generation of protein isoforms that have specific functions. Different splicing factors can be involved in this process, but the roles that individual factors have in the regulation of specific subsets of genes are not always well understood. Son is a member of the serine-arginine-rich (SR) protein family of splicing factors and is essential for maintaining the correct nuclear organisation of pre-mRNA processing factors. On page 4286, Paula Bubulya and co-workers now show that Son is also important for the selection of alternative splicing sites and in maintaining mRNA levels of genes that regulate chromatin organisation and mitotic spindle organisation. By stably expressing a β-tropomyosin minigene in HeLa cells, they demonstrate that the N-terminus of Son is required for its localisation to a transcription site and that depletion of Son results in altered splicing of this gene. Furthermore, Son knockdown leads to defective mitotic spindle organisation during metaphase and to changes in gene expression and splicing of numerous targets. Among the pre-mRNAs that are alternatively spliced are the chromatin-modifying enzymes ADA, HDAC6 and SetD8, and the authors speculate that this, in turn, affects epigenetic regulation of gene expression.