Evolutionary expression of the neuronal form of the src protein in the brain

The protooncogene src encodes two proteins, designated pp60(c-src+) and pp60(c-src). pp60(c.src+) is expressed only in neurons, whereas pp60(c-src) is expressed in neuronal and nonneuronal cells. pp60(c-src+) differs from pp60(c-src) in that it contains in insert of 6 amino acids. To study the evolutionary conservation of the 6-amino acid insert, the expression of pp60(c-src+) in the brain of animals from different classes was assayed by using pp60(c-src+)-specific antibodies raised against a synthetic peptide corresponding to the insert. pp60(c-src+) was detected only in the brain of mammals, birds, and reptiles, but not amphibians and fish, whereas pp60(c-src) was present in the brain of all animals tested, including lobster (invertebrate). These findings indicate that pp60(c-src+) may play a role in events associated with higher brain function, such as neuronal plasticity.