Neuregulin 1 (NRG1) was originally identified as a 44 kD glycoprotein that interacts with NEU/ERBB2 receptor tyrosine kinase to increase the phosphorylation of tyrosine residues. A variety of different isomers are produced from NRG1 gene by alternative splicing. These subtypes include heregulins (HRGs), nerve growth factors (GGFS), and sensory and motor neuron-derived factors (SMDF). Neuregulin and its various subtypes are derived from a family of four structurally related proteins that are part of the EGF protein family. These proteins play multiple roles not only in nervous system development but also in vertebrate embryonic development, including heart development, neurembrane and oligodendrocyte differentiation, some aspects of neural development, and the formation of neuromuscular synapses.