Journal of Neuroscience, Vol 15, 5660-5667, Copyright © 1995 by Society for Neuroscience
Ligand-induced growth cone collapse: amplification and blockade by variant GAP-43 peptides
M Igarashi, WW Li, Y Sudo and MC Fishman
Developmental Biology Laboratory, Massachusetts General Hospital, Charlestown 02129, USA.
Growth cones are powerful amplifiers for signals from the microenvironment.
Their collapse can be triggered by cell surface components of myelin and
brain membranes, as well as by soluble ligands, including
neurotransmitters. GAP-43 is a protein concentrated on the inner surface of
the growth cone membrane. Assayed in isolation, it interacts with the
heterotrimeric protein, G(o), and in oocytes it amplifies the effects of
ligand-triggered G protein activation. We wished to examine whether GAP-43
serves to amplify signals at the growth cone. The G(o) stimulating region
of GAP-43 is encoded in the 10 amino acids (MLCCMRRT-KQ) of the first exon.
We examined the effect of this peptide upon chick dorsal root ganglion
growth cone collapse and neurite retraction triggered by brain membranes or
myelin, as well as by serotonin. We find that application of the GAP-43
1-10 peptide amplifies the effects of all three ligands. The amplification
is greater when GAP-43 1-10 is injected intracellularly. Peptides with
amino acid substitutions for the two cysteine residues manifest parallel
changes in growth cone collapse and G(o) stimulation. In particular,
tyrosine or methionine substitutions cause the peptide to inhibit G(o) and
to block induced growth cone collapse. The GAP-43 peptides therefore
regulate the sensitivity of growth cones to extrinsic signals. The modified
peptides serve as a starting point for the design of reagents to enhance
CNS regeneration.