The RNA-binding protein Fox2 regulates adherens junction integrity in the developing cerebral cortex of the mouse embryo

The RNA-binding protein Fox2 is an alternative splicing regulator that promotes splicing of epithelial isoforms of numerous targets some of which are cell adhesion components. Because of its specific function to regulate splicing of epithelial isoforms it has been suggested that Fox2 prevents epithelial-mesenchymal transitions. In agreement with this downregulation of Fox2 has been linked to an invasive phenotype of tumor cells. Whereas this shows that studying functions of Fox2 is of general interest, in vivo studies in the mouse have not been performed.
In the developing cerebral cortex of the mouse embryo Fox2 is expressed in post-mitotic neurons of the cortical plate as well as in basal progenitors of the intermediate zone and in radial glia cells (RGCs; the neural stem cells) of the ventricular zone (VZ). RGCs that derive from neuroepithelial cells at the onset of neurogenesis are arranged in a columnar fashion in the VZ and are highly polarized. They contain an apical process that forms an endfoot attached to the VZ surface and a basal process that is attached to the pial surface. Adherens junctions that are located at the basolateral membranes of the apical endfeet and that inter-connect RGCs are required to maintain their apical-basal polarity and the architecture of the developing cerebral cortex. To study its function in the developing cerebral cortex in vivo we knocked down Fox2 in this region by in utero electroporation of shRNAs. Remarkably, Fox2 knockdown resulted in disassembly of the adherens junctions of apical endfeet and loss of apical-basal polarity of RGCs, a complete disorganization of the architecture of the cerebral cortex and the formation of rosette-like structures that may resemble neuroepithelial tumors. Since the aberrant splicing of Fox2 targets may cause this phenotype we are now comparing splicing patterns of these targets in control knockdown versus Fox2 knockdown brains.