Transient expression of GAP-43 in nonneuronal cells of the embryonic chick limb.

Growth-associated protein (GAP)-43 is highly expressed in neuronal growth cones during periods of axonal outgrowth in development and regeneration of the nervous system. Although GAP-43 is generally considered to be neuron-specific, it is also expressed in some glial cells of the peripheral and central nervous systems and in at least two populations of mesodermally-derived cells in the developing chick limb. GAP-43 mRNA is expressed transiently in developing limbs; although this expression is correlated temporally with the ingrowth of neurites and axons to the limbs, it appears to be independent of nerves. Immunoreactivity for GAP-43 colocalizes in some developing limb muscle and GAP-43 mRNA and protein are particularly abundant in the interdigital mesenchyme that undergoes programmed cell death. GAP-43 has been postulated to mediate rapid changes in cell shape in neurons and glial cells and may serve a similar function in myoblasts fusing to form myotubes and in apototic and phagocytic cells of the interdigital mesenchyme.