A fast axonally transported protein of the frog sciatic sensory axons undergoes similar qualitative changes during regeneration in vitro and in vivo.

The adult frog sciatic sensory neurons have been shown to regenerate in vitro. If a crush injury is made at the beginning of culture, regeneration starts after 3.4 days and proceeds at a rate of approximately 0.8 mm/day for several days. Two-dimensional gel electrophoresis was used to study the patterns of radiolabeled, fast axonally transported proteins during the first 7 days of regeneration. Interest was focused on one protein, referred to as rrp31 (regeneration-related protein 31), which changed in apparent pI from 4.9 to 5.3 when the outgrowth of new fibers started. The change was noticeable 3 days after injury and became prominent during day 5 of culturing. By day 7 the pI changed again, this time toward the original value. The in vitro results were supported by experiments in vivo. In this case the change occurred earlier, with a peak only 3 days after injury, after which the pI decreased. If adenosine at 1 mM was included in the culturing medium, the outgrowth of sensory axons was inhibited in a nontoxic way, and the pI changes of rrp31 were prevented. The temporal nature of the pI changes suggests a role for rrp31 in the initiation of the regeneration process.