Tyrosine phosphorylation of QKI mediates developmental signals to regulate mRNA metabolism.

The selective RNA-binding protein QKI is essential for myelination in the central nervous system (CNS). QKI belongs to the family of signal transduction activators of RNA (STARs), characteristic of binding RNA and signaling molecules, therefore is postulated to regulate RNA homeostasis in response to developmental signals. Here we report that QKI acts downstream of the Src family protein tyrosine kinases (Src-PTKs) during CNS myelination. QKI selectively interacted with the mRNA encoding the myelin basic protein (MBP). Such interaction stabilized MBP mRNA and was required for the rapid accumulation of MBP mRNA during active myelinogenesis. We found that the interaction between QKI and MBP mRNA was negatively regulated by Src-PTK-dependent phosphorylation of QKI. During early myelin development, tyrosine phosphorylation of QKI in the developing myelin drastically declined, presumably leading to enhanced interactions between QKI and MBP mRNA, which was associated with the rapid accumulation of MBP mRNA and accelerated myelin production. Therefore, developmental regulation of Src-PTK-dependent tyrosine phosphorylation of QKI suggests a novel mechanism for accelerating CNS myelinogenesis via regulating mRNA metabolism.