DEVELOPMENTAL-STUDY OF THE EXPRESSION OF B50 GAP-43 IN RAT RETINA/

B50/GAP-43 has been implicated in neural plasticity, development, and regeneration. Several studies of axonally transported proteins in the optic nerve have shown that this protein is synthesized by developing and regenerating retinal ganglion cells in mammals, amphibians, and fi sh. However, previous studies using immunohistochemistry to localize B 50/GAP-43 in retina have shown that this protein is found in the inner plexiform layer in adults. Since the inner plexiform layer contains t he processes of amacrine cells, ganglion cells, and bipolar cells to d etermine which cells in the retina express B50/GAP-43, we have now use d in situ hybridization to localize the mRNA that codes for this prote in in the developing rat retina. We have found that B50/GAP-43 is expr essed primarily by cells in the retinal ganglion cell layer as early a s embryonic day 15, and until 3 weeks postnatal. Some cells in the inn er nuclear layer, possibly a subclass of amacrine cells, also express B50/GAP-43 protein and mRNA; however, the other retinal neurons-bipola r cells, photoreceptors, and horizontal cells express little, if any, B50/GAP-43 at any stage in their development. Early in development, th e protein appears in the somata and axons of ganglion cells, while lat er in development, B50/GAP-43 becomes concentrated in the inner plexif orm layer, where it continues to be expressed in adult animals. These results are discussed in terms of previous proposals as to the functio ns of this molecule.