Both Schwann cell and axonal defects cause motor peripheral neuropathy in Ebf2-/- mice.

Charcot-Marie-Tooth neuropathies are frequent hereditary disorders of the nervous system and most cases remain without a molecular definition. Mutations in transcription factors have been previously associated to various types of this disease. Mice carrying a null mutation in Ebf2 transcription factor present peripheral nerve abnormalities. To get insight into Ebf2 function in peripheral nervous system, here we characterize the peripheral neuropathy affecting these mice. We first show that Ebf2 is largely expressed in peripheral nerve throughout postnatal development, its expression being not only restricted to non-myelin forming Schwann cells, but also involving myelin forming Schwann cells and the perineurium. As a consequence, the onset of myelination is delayed and Schwann cell differentiation markers are downregulated in Ebf2-/- mice. Later in development, myelin pathology appears less severe and characterized by isolated clusters of hypomyelinated fibers. However, we find defects in the nerve architecture, such as abnormalities of the nodal region and shorter internodal length. Furthermore, we demonstrate a significant decrease in axonal calibre, with a lack of large calibre axons, and a severe impairment of motor nerve conduction velocity and amplitude, whereas the sensory nerve parameters are less affected. Interestingly, a clinical case with peripheral motor neuropathy and clinical features similar to Ebf2-/- mice phenotype was associated with a deletion encompassing EBF2 human genomic locus. These findings demonstrate that Ebf2 is a new molecule implicated in peripheral nerve development and a potential candidate gene for peripheral nerve disorders.

The Transcription Factors EBF1 and EBF2 Are Positive Regulators of Myelination in Schwann Cells.

Myelin formation by Schwann cells is tightly controlled by multiple pathways and regulatory molecules. The Ebf2 gene, belonging to the Ebf family of transcription factors regulating cell development and differentiation, is expressed in Schwann cells, and Ebf2 knockout mice show peripheral nerve defects. We also found that Ebf1 is expressed in Schwann cells. To investigate Ebf function in myelination, we silenced Ebf genes in myelinating dorsal root ganglia cultures. Combined downregulation of Ebf genes leads to a severe impairment of myelin formation that is completely rescued by their specific overexpression, suggesting that the expression level of Ebf genes strongly influences axon myelination. In addition, by profiling Ebf target genes, we found several transcripts belonging to pathways actively involved in peripheral myelination, including Gliomedin, a gene with a role in the formation of the nodes of Ranvier and recently implicated in the pathogenesis of the nodo-paranodopathies. Our results suggest that Ebf genes act as positive regulators of myelination and directly regulate the promoter of Gliomedin.