ABNORMAL LIMB REGENERATION IN THE SHORT-TOES MUTANT OF THE AXOLOTL, AMBYSTOMA-MEXICANUM - STUDIES OF AGE, LEVEL OF AMPUTATION, AND EXTRACELLULAR-MATRIX

Limb regeneration in the short-toes axolotl is impaired. Our goal was to characterize the regeneration process in this mutant by histologica l and immunocytochemical methods. Previous research indicates that age and a defective basement membrane may be instrumental factors in shor t-toes axolotl regeneration (Del Rio-Tsonis et al. [1992] Proc. Natl. Acad. Sci. U.S.A., 89:5502-5506). The present results show that limb r egeneration can occur even in older (1-2-year-old) short-toes axolotls . The process was always significantly delayed, but the time required for complete regeneration varied. Even so, the basement membrane of sh ort-toes regenerates showed no differences in thickness or shape compa red with wild-type regenerates. Distally amputated short-toes limbs ga ve rise to more digits in the regenerate, indicating that regeneration may be somewhat dependent on the level of amputation. Since extracell ular matrix (ECM) remodeling occurs extensively during regeneration, w e compared the ECM of the short-toes and wild-type regenerates using m onoclonal antibodies (mAbs) MT2 and ST1 (Tassava et a1.[1996] Wound Re p. Reg., 4:75-81). The short-toes regenerates showed decreased reactiv ity to mAb MT2, which identifies type XII collagen, an ECM protein tha t is normally unregulated during regeneration, and increased reactivit y to mAb ST1, which identifies a limb ECM component that typically und ergoes breakdown in the distal stump. Thus, impaired regeneration in t he short-toes axolotl is correlated with impaired ECM remodeling in th e distal limb stump. This supports the view that ECM remodeling plays an important role in regeneration. (C) 1997 Wiley-Liss, Inc.