Proteoglycan regulation of goldfish retinal explant growth on optic tectal membranes

Regenerating goldfish retinal explants cultured on poly-L-lysine overlaid with membranes isolated from 21-day regenerating 1/3 anterior optic tectum (Ant. OTec) exhibited extensive defasciculated neurite outgrowth. Heparatinase treatment of membranes caused the complete inhibition of neurite outgrowth on that substrate. Western blot analysis showed that the OTec membranes contain a 300 kDa heparan sulfate proteoglycan. Explants cultured on 21-day regenerating 1/3 Ant. OTec membranes in the presence of 1 mM beta-xyloside, an axonal proteoglycan synthesis inhibitor, showed a significant reduction in the number of neurites per explant and in the average neurite length. Taken all together, the present results provide evidence that a 300-kDa membrane HSPG present in the Ant. OTec is necessary for axonal outgrowth and that axonal PGs are involved in modulating outgrowth on 21-day regenerating 1/3 Ant. OTec membranes.