Model for regulation of NAB expression. The figure indicates a model for regulation of NAB proteins during myelination, based on the requirement of NAB proteins for peripheral nerve myelination. In the first model (A), neuregulin/erbB signaling (and/or other axon-dependent signals) trigger expression of Egr2/Krox20 in myelinating Schwann cells, and the induction of NAB proteins by binding of Egr2/Krox20 acts as a negative feedback control to limit activation of specific target genes that are important for myelination. B) The second model suggests that co-induction of Egr2 and NAB proteins is mediated by neuregulin-activated expression of ETS factors. Activation of ETS factors induces sufficient amounts of NAB proteins so that an Egr2/NAB complex can actively repress specific target genes. It is noted that these two models are not necessarily mutually exclusive and could apply to different target genes in different tissues.