Maintenance and degradation of proteins in intact and severed axons: implications for the mechanisms of long-term survival of anucleate crayfish axons

Abstract

Protein maintenance and degradation are examined in the severed distal (anucleate) portions of crayfish medial giant axons (MGAs), which remain viable for over 7 months following axotomy. On polyacrylamide gels, the silver-stained protein banding pattern of anucleate MGAs severed from their cell bodies for up to 4 months remains remarkably similar to that of intact MGAs. At 7 months postseverance, some (but not all) proteins are decreased in anucleate MGAs compared to intact MGAs. To determine the half-life of axonally transported proteins, we radiolabeled MGA cell bodies and monitored the degradation of newly synthesized transported proteins. Assuming exponential decay, proteins in the fast component of axonal transport have an average half-life of 14 d in anucleate MGAs and proteins in the slow component have an average half-life of 17 d. Such half-lives are very unlikely to account for the ability of anucleate MGAs to survive for over 7 months after axotomy.

Degeneration, Trophic Interactions, and Repair of Severed Axons: A Reconsideration of Some Common Assumptions

“…Axotomy does not necessarily remove all major sources of trophic support from the distal segment, which can have a major trophic dependence on proteins received from various combinations of adjacent glia, neurons, or axonal protein synthesis (14-16, 25, 37-40). (Slow turnover of existing axonal proteins may also be important [41][42][43][44][45][46].) 3.…”

Medium weight neurofilament mRNA in goldfish Mauthner axoplasm

“…First, since one mRNA can be translated many times, transport of mRNA from the cell body to the axonal compartment followed by synthesis of proteins within the axon would be a more efficient mechanism to supply the axon with protein than transport of each protein from the cell body to the axon. Second, since slowly-transported axonal proteins are estimated to have half-lives on the order of days to weeks [20,23] and the rate of axonal transport of cytoskeletal proteins such as actin, tubulin, and the neurofilament proteins is 0.25-3 mm/day [3], significant protein degradation would be expected to occur during transport, especially for long axons. These degraded cytoskeletal proteins might be supplemented by local axoplasmic protein synthesis.…”

Spontaneous Firing in the Isolated Anucleate Axonal Segment of an Identified Crayfish Motoneuron

“…In addition, in crayfish or squid giant axons, endogenous synthesis of axoplasmic proteins appears to be present in the periaxonal glia Lasek et al, 1977;Sheller and Bittner, 1992;Tanner et al, 1995). Koenig and Giuditta (1999) pointed out that the total axonal protein or RNA content of an axon can be much larger than that of its cell body, depending on the diameter and length of the axon.…”

“…Koenig and Giuditta (1999) pointed out that the total axonal protein or RNA content of an axon can be much larger than that of its cell body, depending on the diameter and length of the axon. Anucleate axons in crustaceans can survive for months (Hoy et al, 1967;Wine, 1973;Bittner and Johnson, 1974;Atwood et al, 1989) and the survival time appears to be dependent on the presence of axoplasmic proteins (Bittner and Mann, 1976;Sheller and Bittner, 1992;Tanner et al, 1995).…”