Autogenous Cross-Regulation Of Quaking mRNA Processing And Translation Balances Quaking Functions In Splicing And Translation

Quaking RNA binding protein (RBP) isoforms arise from a single Quaking gene, and bind the same RNA motif to regulate splicing, stability, decay, and localization of a large set of RNAs. However, the mechanisms by which the expression of this single gene is controlled to distribute appropriate amounts of each Quaking isoform to regulate such disparate gene expression processes are unknown. Here we explore the separate mechanisms that regulate expression of two isoforms, Quaking-5 (Qk5) and Quaking-6 (Qk6), in mouse muscle cells. We first demonstrate that Qk5 and Qk6 proteins have distinct functions in splicing and translation respectively, enforced primarily through differential subcellular localization. Using isoform-specific depletion, we find both Qk5 and Qk6 act through cis and trans post-transcriptional regulatory mechanisms on their own and each others transcripts, creating a network of auto- and cross-regulatory controls. Qk5 has a major role in nuclear RNA stability and splicing, whereas Qk6 acts through translational regulation. In different cell types the cross-regulatory influences discovered here generate a spectrum of Qk5/Qk6 ratios subject to additional cell type and developmental controls. These unexpectedly complex feedback loops underscore the importance of the balance of Qk isoforms, especially where they are key regulators of development and cancer.