THE IN-VIVO REGULATION OF PIONEER AXON GROWTH BY FGF-2 AND HEPARAN-SULFATE PROTEOGLYCANS IN CULTURED EMBRYOS OF THE COCKROACH

Antibody perturbation experiments on cultured cockroach embryos demons trated that a localized source of an FGF-2-like immunoreactive molecul e in the head is required for the proper growth of pioneer axons in th e leg. The study of axon growth in various fragments of cultured embry os and in the presence of various conditioned media showed that FGF-P is needed to counteract the effects of an inhibitor of axon growth pro duced in the body trunk of the embryo. Endogenous heparan sulfate prot eoglycans mediate these effects of FGF-2 on axon growth. The results o f experiments with FGF-2 and/or body trunk axon growth inhibitor added to the culture medium indicate that more globally and uniformly distr ibuted molecules may play as important a role in axon guidance as the more spatially restricted guidance cues. The results are interpreted i n terms of a model that is consistent with a role for the FGF-2 recept or in axon growth.