Retrograde axonal transport of locally synthesized proteins, e.g., actin and heat shock protein 70, in regenerating adult frog sciatic sensory axons

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Abstract
The local synthesis and subsequent retrograde axonal transport of [35S]methionine‐labelled proteins was studied in the in vitro regenerating adult frog sciatic sensory axons. By the use of a three compartment culture system, proteins in the outgrowth region were selectively labelled. After 2 days in culture a rise in TCA‐insoluble radioactivity was detected in the dorsal root ganglia, which could be prevented by the addition of viblastine or 2,4‐dinitrophenol to the nerve proximal to the crush site. Two‐dimensional polyacrylamide gel electrophoresis of ganglionic proteins revealed a pattern of 35 labelled polypeptides with apparent molecular masses (Mm) ranging from < 15 to 95 kDa and with isoelectric points (pI) ranging from 4.5 to 6.5. The major ones, representing about 75% of the activity in a gel, were of Mm/pI 47/5.4, 48/6.1, ©57/6.0, 62/5.2, 65/4.9–5.0, 65/5.2, and 81/5.4 respectively. One of these polypeptides (47/5.4) was identified as actin and another (81/5.4) as a member of the heat shock protein 70 family. The spots at 65/4.9‐‐5.0 were tubulin isoforms. There was a striking similarity between transported proteins on one hand, and proteins synthesized in the injured nerve on the other, with respect to the Mm/pI of at least 14 protein species. The results suggest that selected set of proteins, synthesized by non‐neuronal cells, e.g., Schwann cells, is transferred to the ganglionic cell bodies by retrograde axonal transport.© 1994 WiIey‐Liss, Inc.