– NRG4 (neuregulin 4) is a member of the neuregulin protein family. The neuregulins consist of four structurally-related proteins that are part of the EGF family of proteins. It has been shown that these proteins have diverse functions in the development of the nervous system and play multiple essential roles in vertebrate embryogenesis including cardiac development, Schwann cell, and oligodendrocyte differentiation, some aspects of neuronal development, as well as the formation of neuromuscular synapses. NRG4 contains 1 EGF-like domain. It activates type-1 growth factor receptors to initiating cell-to-cell signaling through tyrosine phosphorylation. NRG4 is a low-affinity ligand for the ERBB4 tyrosine kinase receptor. It concomitantly recruits ERBB1 and ERBB2 coreceptors, resulting in ligand-stimulated tyrosine phosphorylation and activation of the ERBB receptors. However, it does not bind to the ERBB1, ERBB2, and ERBB3 receptors.