THE NEURITE-PROMOTING EFFECT OF LAMININ IS MEDIATED BY DIFFERENT MECHANISMS IN EMBRYONIC AND ADULT REGENERATING MOUSE OPTIC AXONS IN-VITRO

Retinal explants from embryonic or adult mice were placed on laminin o r merosin substrates and the outgrowth of optic fibers was assayed und er serum-free conditions. Both substrates strongly promoted outgrowth. A blocking antibody to the beta 1/beta 3 integrin subunits completely blocked laminin-dependent growth of embryonic optic fibers but had no detectable effect on adult fibers. Similarly, a blocking antibody aga inst the main neurite-promoting region within the globular domain of t he E8 fragment of laminin inhibited growth of embryonic fibers but had no effect on adult optic fibers. The beta 1 integrin subunit was iden tified immunohistochemically on both embryonic and adult fibers. These findings indicate that adult fibers have lost the beta 1 function whi ch dominates laminin-dependent growth in embryonic fibers but express a receptor for laminin-dependent growth that is not detectable in embr yonic fibers. These findings suggest that there are intrinsic differen ces between embryonic and adult optic fibers that may have implication s for regenerative failure in the central nervous system of adult mamm als. (C) 1997 Academic Press