The ERBB3 gene is essential for the proper development of the neural crest (NC) and its derivative populations such as Schwann cells. As with all cell fate decisions, transcriptional regulatory control plays a significant role in the progressive restriction and specification of NC derived lineages during development. However, little is known about the sequences mediating transcriptional regulation of ERBB3 or the factors that bind them.

Myelin is essential for the rapidity of saltatory nerve conduction, and also provides trophic support for axons to prevent axonal degeneration. Two critical determinants of myelination are SOX10 and EGR2/KROX20. SOX10 is required for specification of Schwann cells from neural crest, and is required at every stage of Schwann cell development. Egr2/Krox20 expression is activated by axonal signals in myelinating Schwann cells, and is required for cell cycle arrest and myelin formation. To elucidate the integrated function of these two transcription factors during peripheral nerve myelination, we performed in vivo ChIP-Seq analysis of myelinating peripheral nerve. Integration of these binding data with loss-of-function array data identified a range of genes regulated by these factors. In addition, although SOX10 itself regulates Egr2/Krox20 expression, leading to coordinate activation of several major myelin genes by the two factors, there is a large subset of genes that are activated independent of EGR2. Finally, the results identify a set of SOX10-dependent genes that are expressed in early Schwann cell development, but become subsequently repressed by EGR2/KROX20.

Myelination of peripheral nerves by Schwann cells depends upon a gene regulatory network controlled by early growth response Egr2/Krox20, which is specifically required for Schwann cells to initiate and maintain myelination. To elucidate the mechanism by which Egr2 regulates gene expression during myelination, we have performed chromatin immunoprecipitation analysis on myelinating rat sciatic nerve in vivo. The resulting samples were applied to a tiled microarray consisting of a broad spectrum of genes that are activated or repressed in Egr2-deficient mice. The results show extensive binding within myelin-associated genes, as well as some genes that become repressed in myelinating Schwann cells. Many of the Egr2 peaks coincide with regions of open chromatin, which is a marker of enhancer regions. In addition, further analysis showed that there is substantial colocalization of Egr2 binding with Sox10, a transcription factor required for Schwann cell specification and other stages of Schwann cell development. Finally, we have found that Egr2 binds to promoters of several lipid biosynthetic genes, which is consistent with their dramatic up-regulation during the formation of lipid-rich myelin. Overall, this analysis provides a locus-wide profile of Egr2 binding patterns in major myelin-associated genes using myelinating peripheral nerve.