Slowly migrating axonal polypeptides. Inequalities in their rate and amount of transport between two branches of bifurcating axons.

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Abstract
Polypeptides in the dorsal root ganglion (L[sodium dodecyl sulfate]5) of the adult rat were radioactively labeled, and components slowly migrating in the sciatic nerve (peripheral axons) and dorsal root (central axons) were analyzed, using SDS[sodium dodecyl sulfate]-polyacrylamide slab gel electrophoresis and fluorography. In particular, the transport rates and amounts of 6 major polypeptides, i.e., the triplet (reference 15; with MW of 200,000, 160,000 and 68,000 daltons), .alpha.- and .beta.-tubulins and actin were compared between the 2 axon branches. In peripheral axons, fronts of the triplet, tubulins and actin migrate at 2-3 mm/d, 9-13 mm/d and .apprx. 19 mm/d, respectively. The corresponding values in central axons are 1-2 mm/d, 3-4 mm/d and .apprx. 4 mm/d, indicating an obvious asymmetry in the transport rate between the 2 branches of bifurcating axons. A greater amount of labeled triplet, tubulins and actin each migrates in peripheral rather than in central axons. Another striking aspect of asymmetry between the 2 branches relates to the tubulins/triplet ratio which is significantly higher in the peripheral branch. Considerable proportions of radioactivities associated with tubulins and actin in the ganglion are nonmigratory, which are thought to derive mostly from periaxonal satellite cells. Most if not all of the labeled triplet is migratory, suggesting a virtual absence of triplet polypeptides in satellite cells. The possible significance of peripheral-central inequalities in slow axoplasmic transport is discussed from the viewpoints of axon volume and axonal outgrowth.