STABILIZING ROLE OF THE BASEMENT-MEMBRANE AND DERMAL FIBERS DURING NEWT LIMB REGENERATION

Background: Following amputation of a newt limb, tissues at the amputa tion site undergo histolysis to give rise to a growth bud, or blastema , but they also provide a base on which the regenerate is constructed. Studies suggest that dermal tissues may differentially resist histoly sis. Methods and Results: To examine stability of tissues at the amput ation site, more than 80 preblastemal staged regenerating limbs were e xamined histologically. Initially, all soft tissues not attached to bo ne retracted and were covered by migrating epithelium. The dermis was seen to be stable during the first week postamputation. Muscle dediffe rentiated and was heavily stained with anti-tenascin antibodies, but t he intact overlying dermis was unstained. Fiber bundles, revealed by s taining with phosphotungstic acid hematoxylin, isolated the dermis fro m dedifferentiating deeper tissues during the first week postamputatio n, but partially broke down during the second week. However, the basem ent membrane (BM) remained as the distalmost intact structure at the a mputation site in all limbs examined. The BM was the foundation for ne w BM synthesis which preceded dermis synthesis in the base of the blas tema during the second week, even while undifferentiated cells were ac cumulating centrally. Conclusions: We suggest that the dermis resists histolysis long enough for new BM to form in continuity with that of t he stump. Dermis formation (dermogenesis) distal to the amputation pla ne begins early as in mammalian healing but is not completed until aft er blastema formation. Thus, factors that inhibit dermal closure appea r to distinguish regenerating from non-regenerating appendages. (C) 19 96 Wiley-Liss, Inc.