Neuregulin

The Neuregulins are a family of four structurally-related proteins that are part of the EGF family of proteins. These proteins have been shown to have diverse functions in the development of the nervous system.

Neuregulin family members
The neuregulin family includes:
 * Neuregulin-1 (NRG1), with numerous discovered isoforms stemming from alternative splicing:
 * Type I NRG1; alternative names: Heregulin, NEU differentiation factor (NDF), or acetylcholine receptor inducing activity (ARIA)
 * Type II NRG1; alternative name: Glial Growth Factor-2 (GGF2);
 * Type III NRG1; alternative name: Sensory and motor neuron-derived factor (SMDF);
 * Type IV NRG1;
 * Type V NRG1;
 * Type VI NRG1; Types IV-VI are proteins with 3 novel N-terminal domains identified in 2004.
 * Neuregulin-2 (NRG2);
 * Neuregulin-3 (NRG3);
 * Neuregulin-4 (NRG4);

In mammals, neuregulin family members are the products the 4 genes, , and  respectively.

ARIA
ARIA plays a role in synapse development, influencing the upregulation of acetylcholine receptor genes beneath the endplate after mammalian motor neurons have made synaptic contact with muscle fibres, hence its name ARIA = Acetylcholine Receptor Inducing Activity.

In fish, birds, and earthworms
NRG-1,2,3 have been found in fish and birds.

mRNA similar to mammalian Pro-NRG2 precursor hase been found in humus earthworm Lumbricidae.