Synthesis and fast axonal transport of proteins in the isolated Aplysia nervous system

Abstract

Fast axonal transport and neuronal protein synthesis was studied in the isolated nervous system of Aplysia californica. The abdominal ganglion with attached pleural-abdominal connectives (PAC) was removed and the ganglion pulse-labelled with [ 35S]methionine for 30 min in vitro. The axon containing connectives were ligated 24–28 mm from the ganglia and the system was perfused with chase media for 6–72 h to allow labelled rapidly transported proteins to accumulate at the ligature. One-dimensional polyacrylamide gel electrophoresis (PAGE) and fluorography was used to analyze the distribution of rapidly transported proteins along the right PAC. By 12 h, a significant accumulation of labelled proteins at the ligature was present but the build up was not complete until 48 h when almost no trailing of rapidly transported proteins was observed. Quantitation of the transport profiles of several rapidly transported protein ssuggested a discontinuous release of proteins from the cell body. Analysis using two-dimensional PAGE revealed 10 major groups of rapidly transported proteins. These proteins were all identified among the total complement of newly synthesized proteins in cell R2. Not all rapidly transported proteins are cleared from the cell body at the same rate. Several of the major groups were no longer present in the neuron cell body 24 h after labelling, indicating that these species are selectively exported; others were still present after 3 days, suggesting that these proteins with a longer residence time have functions in both somatic and axonal regions of the neuron.