PROTEIN-SYNTHESIS AND RELEASE BY NORMAL AND LESIONED AXOLOTL PERIPHERAL-NERVES

Previous studies in urodeles (Holder et al., 1982, J. Physiol. 326: 37 1; Holder et al, 1984, Proc. R. Soc. Lend B 222: 477; Aaronson et al., 1995, Neuroscience 66: 201) have shown that regenerating axons of per ipheral nerves tend to grow toward distal nerve stumps, which is consi stent with the hypothesis that axonal growth may be stimulated by fact ors released from degenerating nerves. In the present study we used tw o-dimensional gel electrophoresis and autoradiography to compare the i ncorporation of radiolabeled methionine into proteins which are synthe sized and released in vitro by segments of normal and previously cut a xolotl sciatic nerves, within the isoelectric point range 2.4-10.6 and molecular weight range 3.6-200 kDa. In the distal portion of nerves c ut 7 days previously in vivo, the synthesis of at least six secreted p roteins was significantly greater than in undamaged nerves. The possib le cellular sources of these proteins was assessed by comparing protei n release from normal nerves with nerve segments maintained in culture for 7 days (in which the contribution from recruited macrophages woul d be expected to be minimal) and segments of nerve which had been froz en and then replaced in sit-a for 7 days (in which the contribution fr om sheath cells would be expected to be minimal). This revealed that f ive of the up-regulated proteins from the lesioned nerves, with appare nt molecular weight (kDa)/isoelectric point values of approximately 12 0/4, 20/5, 19/5.3, 16.5/6.4-6.5, and 7/4.2 are predominantly sheath ce ll products, while one (19/5.8-6.0) may be secreted mainly by macropha ges (or other cells) which center the frozen nerve segments. The ident ity of these proteins and their possible involvement in nerve repair r emain to be determined. (C) 1995 Academic Press, Inc.