Epidermis, basement membrane, and connective-tissue healing after amputation of mouse digits: implications for mammalian appendage regeneration.

Soft tissues from amputation sites of mice were examined at both light and electron microscope levels to determine whether features of growth buds (blastemas), which are necessary for amphibian limb regeneration, exist in nonregenerating mice. Several such features were found. A small area of the wound bed was covered by wound epithelium which, as in regenerating newt limbs, initially lacked an underlying basement membrane. Serially sectioned digits revealed blastemalike growth in the subdermal layer surrounding periosteal chondrogenic cells. Mesenchymelike cells were seen among the fibroblasts and leucocytes within the proliferating tissues. However, no evidence of dedifferentiation was seen in the dermis, which persisted as an apparent intact obstruction to growth bud formation. Existence of the essential ingredients of growth buds and soft-tissue proliferation adjacent to chondrogenic cells proximally suggest that the tissues of mammalian healing may differ quantitatively rather than qualitatively from tissues of appendage regeneration. This premise is encouraging for efforts at growth enhancement in mammals.