GAP-43: putting constraints on neuronal plasticity.

The brain must balance the need for synaptic precision with the ability to generate and change connectivity patterns in response to environmental stimuli. GAP-43 is a phosphoprotein associated with the cytosolic surface of the membrane, and is one of the most abundant among the small subset of total cellular proteins transported to the growth cone. It appears to play an unusual role amplifying signals from the microenvironment. One of the several ways to perform this task involves interaction of GAP-43 with the G protein transduction cascade. In mice rendered GAP-43 null by homologous recombination, some nerves manifest aberrant growth at decision points, such as the optic chiasm. Thus, GAP-43 may work via modulation of signaling cascades, rather than autonomously causing growth, and could serve to keep plasticity within constraints needed to generate and maintain accurate synaptic wiring.