Changes in Perikaryal organelles during axonal regeneration in goldfish retinal ganglion cells: An analysis of protein synthesis and routing

Abstract

Routing of newly synthesized proteins through the perikaryal organelles of goldfish retinal ganglion cells was studied by subjecting isolated retinas to pulse-chase incubation in [ 3H]proline-containing media and then examining the retinal ganglion cells by quantitative electron microscopic autoradiography. Regenerating cells 6 days after optic tract transection were compared to sham-operated controls and normal cells. The results of this study, together with our previous observations on 14- and 30-day regenerating cells have led us to the following conclusions. (1) Increased labeling of nucleus and nucleolus was seen at 6 days, consistent with increased synthesis of nucleoprotein during the early stages of regeneration. (2) At 6 days, when the regenarating cells were beginning to enlarge, the relative volume of the rough endoplasmic reticulum (RER) was somewhat reduced, but there was no evidence of a major disturbance of the RER comparable to that characteristic of chromatolysis in other axotomized cells. At 14 and 30 days the relative volume of RER was the same as in control cells, indicating that its absolute volume increased in parallel with the increase in cell size. (3) In contrast to the changes in the RER, the relative volume occupied by free polyribosomes was significantly increased at all 3 regeneration times. Nevertheless, the proportion of total protein synthesized in the RER progressively increased from 6 to 30 days whereas the proportion synthesized in the free polysomes decreased. (4) The relative volume of the Golgi apparatus remained constant throughout regeneration. However, because of increased grain density in this organelle as well as increased cell size, the amount of newly synthesized protein delivered to the Golgi apparatus was significantly increased at all 3 regeneration times examined. (5) Smooth membrane elements, which may relay material from RER to Golgi apparatus, were greatly increased in relative volume and percentage of total label at all 3 regeneration times. During regeneration these elements may contribute to an increase in fast axonal transport of membranenous organelles.