Identifying novel components of the SRPK signalling pathway that is implicated in human developmental disorders

Ser-Arg Protein Kinase (SRPK) was originally characterised as a splicing factor kinase that controls spliceosome assembly. However, recent data from our lab and others suggests that SRPK may have wider functions in stem cells and development. For example, we find that SRPK phosphorylates the RNF12 E3 ubiquitin ligase, which stimulates RNF12 activity and nuclear anchoring with transcription factor substrates such as REX1. This in turn regulates expression of developmental genes, including those involved in embryonic stem cell pluripotency and differentiation to neuronal and germ cell lineages. Accordingly, SRPK and RNF12 are mutated in related human developmental disorders; in the case of RNF12, the recently named Tonne-Kalscheuer Syndrome, an X-linked syndromic form of intellectual disability.
The discovery that SRPK phosphorylates exciting developmental regulators prompted us to perform a comprehensive phosphoproteomic survey for further SRPK substrates in mESCs. This analysis identifies a cohort of phosphopeptides that are dynamically regulated by SRPK activity and display characteristic SRPK phosphorylation motifs, suggesting that these may be direct substrates. We therefore aim to explore the role of SRPK in regulating novel substrates. We will use biochemistry and targeted phosphoproteomics map SRPK phosphorylation sites, and CRISPR/Cas9 engineering to determine the function of SRPK substrate phosphorylation in pluripotent stem cell derived neurons. This project will uncover novel roles of SRPK that are important for human neurological development and functioning.