Stabilizing role of the basement membrane and dermal fibers during newt limb regeneration.

BACKGROUND

Following amputation of a newt limb, tissues at the amputation 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 histolysis.

METHODS AND RESULTS

To examine stability of tissues at the amputation site, more than 80 preblastemal staged regenerating limbs were examined histologically. Initially, all soft tissues not attached to bone retracted and were covered by migrating epithelium. The dermis was seen to be stable during the first week postamputation. Muscle dedifferentiated and was heavily stained with anti-tenascin antibodies, but the intact overlying dermis was unstained. Fiber bundles, revealed by staining with phosphotungstic acid hematoxylin, isolated the dermis from dedifferentiating deeper tissues during the first week postamputation, but partially broke down during the second week. However, the basement membrane (BM) remained as the distalmost intact structure at the amputation site in all limbs examined. The BM was the foundation for new BM synthesis which preceded dermis synthesis in the base of the blastema during the second week, even while undifferentiated cells were accumulating centrally.

CONCLUSIONS

We suggest that the dermis resists histolysis long enough for new BM to form in continuity with that of the stump. Dermis formation (dermogenesis) distal to the amputation plane begins early as in mammalian healing but is not completed until after blastema formation. Thus, factors that inhibit dermal closure appear to distinguish regenerating from non-regenerating appendages.