Three subpopulations of fast axonally transported retinal ganglion cell proteins are differentially trafficked in the rat optic pathway

Post-Golgi trafficking of the major fast axonally transported (FT) proteins was investigated in the rat optic pathway. Following intra-ocular injectio n of S-35-methionine, radiolabeled FT proteins in the optic tract (OT) and superior colliculus (SC) were analyzed by two-dimensional polyacrylamide ge l electrophoresis (2D-PAGE) and fluorography. Twenty FT proteins, including a known plasma membrane protein (SNAP-25) and synaptic vesicle protein (sy naptobrevin-2), displayed consistent 2D-PAGE migration behavior and were ch osen for densitometric quantitative analysis. Results showed that at least three subpopulations of the 20 FT proteins could be differentiated based on their trafficking behavior to axons (OT) vs, terminals (SC). To assess whe ther Golgi-independent processes (e.g., delayed somal release and/or retrog rade transport) could account for the differential compartmentation behavio r between the three FT classes, we assessed whether radiolabeled FT protein s became redistributed in the optic pathway following a nerve transection b lockade. The results showed that radiolabelled FT proteins did not show a q uantitative change in their axon vs. terminal compartmentation in response to disconnection from cell bodies or targets. Thus, the three classes of fa st axonally transported proteins were likely trafficked to distinct destina tions in the optic pathway by Golgi sorting mechanisms. (C) 2000 Wiley-Liss , Inc.