Role of protein kinase C in selective inhibition of mouse retinal neurites during contacts with chondroitin sulfates.

Chondroitin sulfate proteoglycans elicit a selective inhibition to neurite growth from ventrotemporal (VT) but not dorsonasal (DN) retina, potentiating the bilateral routing of axons in the mouse optic chiasm. We examined whether this selective response is mediated by a difference in protein kinase C (PKC) expression. Effects of suppressing PKC activity in explant preparations of embryonic day 14 retinae with inhibitor Gö6976 or Ro-32-0432 abolished the chondroitin sulfate inhibition to the VT neurites but had no effect to the DN neurites. Whether these responses rely on a difference in expression of PKC in the growth cones was examined using antibodies against six isozymes of PKC. Among these the alpha, betaI and epsilon isozymes were expressed prominently in the retinal growth cones; whilst the betaII, delta and gamma isozymes were barely detected. Moreover, while the alpha and epsilon isozymes were abundant in the filopodial and lamellipodial processes, the betaI isozyme was restricted largely in the core region of the growth cones. Despite these subtype specific localization, there was no significant difference in expression of any of these PKC isozymes between growth cones from VT and DN retina, indicating that the selective response to chondroitin sulfates is not likely generated by a regulation of PKC expression, but by expression of surface molecules that interact with chondroitin sulfate proteoglycans.