MKRN2 physically interacts with GLE1 to regulate mRNA export and zebrafish retinal development

The canonical mammalian mRNA export process is thought to terminate at the cytoplasmic face of the nuclear pore complex through mRNP remodeling. We conducted a stringent affinity-purification mass-spectrometry-based screen of the physical interactions of human RNA-binding E3 ubiquitin ligases. The resulting protein-interaction network revealed unexpected interactions between the RNA-binding E3 ubiquitin ligase MKRN2 and GLE1, a DEAD-box helicase activator implicated in mRNA export termination. We assessed MKRN2 epistasis with GLE1 in a genetically tractable zebrafish model. Strikingly, morpholino-mediated knockdown or CRISPR/Cas9-based knockout of MKRN2 partially rescued retinal developmental defects seen upon GLE1 depletion. Next, using iCLIP, we showed that MKRN2 binds preferentially to the 3'UTR of a diverse subset of mRNAs. Next-generation sequencing of fractionated cell extracts revealed that nuclear export of MKRN2-associated mRNAs is enhanced upon knockdown of MKRN2. Taken together, these results indicate that MKRN2 selectively interacts with GLE1 to regulate mRNA nuclear export and retinal development. Overall design: Examination of the transcriptome-wide RNA-binding profile of EGFP-MKRN2 by individual-nucleotide resolution crosslinking and immuno-precipitation sequencing (iCLIP)