Cloning and characterization of two neural-salient serine/arginine-rich (NSSR) proteins involved in the regulation of alternative splicing in neurones.

In neurones, alternative splicing regulates the functions of many gene products. However, the molecular basis of neural-specific splicing, and how splicing regulation is modulated in different neurones remains to be determined. We cloned two new SR proteins, Neural-salient SR proteins (NSSR) 1 and 2, which are present at higher levels in brain and testis. During the differentiation, NSSR 1 is detected only in the neuronal stage. Both the purified recombinant NSSR 1 and 2 proteins enhance the in vitro splicing activity of nuclear extract. Moreover, recombinant NSSR 1 protein enhances the assembly of ribonucleoprotein complexes with S100 fraction. Over-expression of NSSR 2 prevents the inclusion of either the Flip or Flop exons in the splicing of the GluR-B gene, resulting in an increase in the abnormal exon-skipping product. In contrast, transient transfection with NSSR 1 promotes the inclusion of the Flip exon so that the abnormal product is spliced to the mature spliced form. This suppression of exon skipping by NSSR 1 is observed even with co-transfection of NSSR 2. NSSR 1 and 2 were cloned from mouse cDNA libraries. Results indicate that NSSR 1 may play a crucial role in the regulation of alternative splicing in neurones.