Investigation of the axonal transport of three acidic, soluble proteins (14-3-2, 14-3-3, and S-100) in the rabbit visual system.

The question of whether three acidic, water-soluble proteins (14-3-2, 14-3-3, and S-100, the first and last known to be brain-specific) are axonally transported was investigated in the rabbit visual system. The water-soluble proteins were obtained from individual optic nerves, combined optic tracts and lateral geniculate bodies, superior colliculi, and, in some instances, retinas at various times (1--56 days) after monocular injections of [3H]leucine. These proteins were separated by a two-step polyacrylamide gel electrophoresis procedure that isolated 14-3-2, 14-3-3, and S-100 almost uncontaminated by other radioactivity. The isolated 14-3-2 and S-100 were demonstrated to be approx. 90% pure by a new method based on retarding the migration of these proteins by immunoadsorption during the first step of electrophoresis. An analysis of the radioactive labeling of the total soluble proteins (TSP) and the isolated acidic proteins revealed that: (1) S-100 was not axonally transported; (2) both 14-3-2 and 14-3-3 were part of one of the slow components of axonal transport (2--4 mm/day); (3) the radioactivity of 14-3-2 and 14-3-3 represented about 2.7% and 3.2%, respectively, of the radioactivity incorporated into the axonally transported TSP; (4) the ultimate distributions of the radioactively labeled 14-3-2 and 14-3-3 were the same (about 70% of each destined for the superior colliculus) and differed from that of the TSP; and (5) the rates of catabolism of the axonally transported 14-3-2 and 14-3-3 were slightly greater than that of the TSP, with half-lives for 14-3-2 and 14-3-3 estimated to be 11 and 10 days, respectively.