EXPRESSION LEVELS OF B-50 GAP-43 IN PC12 CELLS ARE DECISIVE FOR THE COMPLEXITY OF THEIR NEURITES AND GROWTH CONES/

To study the role of the protein B-50/GAP-43 in NGF-induced neurite ou tgrowth, a number of stable PC12 subclones with either very low or con siderably enhanced expression levels of the protein were selected. Cel l bodies of subclones with suppressed B-50 expression (-B2, -B5, or -B 12) possessed a relative small spherical shape and, on NGF-treatment f or 7 d, developed processes that were virtually devoid of branches and that mostly bore short or blunt-ended growth cones. Cells of subclone s with overexpression of B-50 (+B3, +B4, or +B11), on NGF treatment, a cquired a flattened, spiky appearance with highly branched neurites po ssessing extended and complex growth cones. Confocal microscopy with i mmunofluorescence for B-50 and F-actin revealed that in neurites and g rowth cones of the B-50-deficient subclone -B2, no detectable B-50 and reduced amounts of filamentous F-actin were present, whereas in overe xpressing +B3 cells, cell membranes, neurites, and complex growth cone s were intensively stained for B-50 and exhibited numerous spikes, in which B-50 was strikingly colocalized with F-actin. These data suggest that, under normal conditions of neuritogenesis, the expression level of B-50 in PC12 cells is decisive for the complexity of neurites and growth. cones.