Premature upregulation of miR-92a’s target RBFOX2 hijacks PTBP splicing and impairs cortical neuronal differentiation

RBFOX2 is an RNA-binding protein crucial for alternative splicing regulation and implicated in several neurodevelopmental disorders. Here, we show that while RBFOX2 is present only at low levels in neural progenitor cells (NPCs), it is upregulated in differentiating neurons of the mouse embryonic neocortex. In-utero- electroporation-induced overexpression resulted in a cellular phenotype characterized by impaired neuronal migration and differentiation. Genome-wide analysis at E15.5 revealed numerous alternative splicing events associated with a mixed NPC- and neuron-like splicing pattern and a significant deviation from the normal splicing developmental trajectory. Remarkably, premature Rbfox2 overexpression induced the inclusion of validated target exons that are otherwise repressed by PTBP2, indicating an antagonistic splicing relationship between these two RNA-binding proteins and highlighting the necessity for strict temporal regulation of their expression during embryonic brain development. Consequently, we showed that the NPC-specific miRNA 92a-3p reduced the expression levels of Rbfox2 in vitro . Furthermore, silencing miR-92a-3p in vivo in the embryonic neocortex led to a significant increase in Rbfox2 levels. Our results therefore demonstrate that RBFOX2 is a crucial player in the NPC-to-neuron splicing switch. Furthermore, we present a novel post-transcriptional mechanism for controlling RBFOX2 levels during early neuronal differentiation via miR-92a-3p silencing.