Identification of SRSF10 as a regulator of SMN2 ISS‐N1. Issue 3 (16th December 2020) - Frederiksen, Sabrina B.
Abstract: Understanding the splicing code can be challenging as several splicing factors bind to many splicing‐regulatory elements. The SMN1 and SMN2 silencer element ISS‐N1 is the target of the antisense oligonucleotide drug, Spinraza, which is the treatment against spinal muscular atrophy. However, limited knowledge about the nature of the splicing factors that bind to ISS‐N1 and inhibit splicing exists. It is likely that the effect of Spinraza comes from blocking binding of these factors, but so far, an unbiased characterization has not been performed and only members of the hnRNP A1/A2 family have been identified by Western blot analysis and nuclear magnetic resonance to bind to this silencer. Employing an MS/MS‐based approach and surface plasmon resonance imaging, we show for the first time that splicing factor SRSF10 binds to ISS‐N1. Furthermore, using splice‐switching oligonucleotides we modulated the splicing of the SRSF10 isoforms generating either the long or the short protein isoform of SRSF10 to regulate endogenous SMN2 exon 7 inclusion. We demonstrate that the isoforms of SRSF10 regulate SMN1 and SMN2 splicing with different strength correlating with the length of their RS domain. Our results suggest that the ratio between the SRSF10 isoforms is important for splicing regulation. Abstract : The antisense‐oligonucleotide drug Spinraza is a new efficient therapy against Spinal Muscular Atrophy (SMA). Spinraza binds to the SMN splicing silencer, ISS‐N1, and functions by inhibiting binding of splicing inhibitory proteins to the splicing silencer. So far only members of the universally expressed hnRNP A1/A2 family have been demonstrated to bind to ISS‐N1 and inhibit SMN splicing. In this study, we show that the splicing factor SRSF10, which is particularly abundant in neuronal tissue, binds to ISS‐N1, and that the long and short isoforms of SRSF10 inhibit SMN splicing with different strength correlating with the length of their RS domain. Our results suggest that the ratio between the SRSF10 isoforms is important for SMN splicing regulation.