EFFECT OF A DIPEPTIDE INHIBITING UBIQUITIN-MEDIATED PROTEIN-DEGRADATION ON NERVE-DEPENDENT LIMB REGENERATION IN THE NEWT

The dipeptide Leu-Ala, which inhibits ubiquitin-mediated protein degra dation, has been shown to act in vitro as an inhibitor of neurite outg rowth of PC12 cells (Hondermarck et al. [1992] Biochem. Biophys. Res. Commun. 189: 280). Using agarose beads as vehicles, we tested, in vivo , the effect of this dipeptide (and the inactive inverse, Ala-Leu, as a control) on limb regeneration in the newt (Triturus cristatus), a ne rve-dependent developmental process. Leu-Ala inhibited the growth of m id-bud blastemas without altering blastema differentiation, while Ala- Leu had no effect. Cytological observations of dipeptide-treated blast emas using Bodian staining or neurofilament antibodies showed that all the blastema tissues were unmodified except with regard to innervatio n. Leu-Ala-treated blastemas were devoid of nerve fibers in the epider mal cap, while the mesenchyme distal to the dipeptide impregnated bead exhibited fewer nerve fibers than did Ala-Leu-treated blastemas, whic h were similar to the control nontreated blastemas. Thus, Leu-Ala, in reducing blastema innervation, inhibits its growth in the same manner as surgical denervation.