87Fig. 5.3 ( a ) P2 amputation ( dashed line ) transects the mid-portion of the bone and completely
removes the nail organ. ( b ) Distal scab formation (S) and circumferential swelling of the digit are
apparent by 6 DPA. ( c ) By 9 DPA, wound closure over the distal stump and wound epidermis
formation (WE) have occurred. Robust chondrogenesis along the periosteal surface ( outlined )
extends perpendicular to the bone stump, not distal to the amputation plane. ( d ) ColII immunos-
taining localized to the periosteal cartilaginous callus at 9 DPA. ( e ) ACAN immunostaining con-
fi rms the presence of a periosteal chondrogenic callus at 9 DPA. ( f ) Immunostaining for the
osteoblast marker Osterix, OSX, shows osteoblasts localized to the 9 DPA periosteal callus and
within the bone marrow space. ( g ) By 15 DPA, the cartilaginous callus has been largely replaced
with woven bone and marrow formation. ( h ) Distal intramembranous bone formation has sealed
the marrow space ( arrowhead ) and the callus has undergone remodeling by 24 DPA. ( i ) At 45
DPA, the amputated digit has completely healed and the ventral tendon has re-inserted into the
bone on the dorsal surface ( arrowhead ). ( j and k ) μCT 3-D renderings and quantifi cation of bone
volume changes illustrate the robust periosteal growth in response to amputation , corresponding to
an overshoot in bone volume, yet no increase in bone length. ( a – i ) Distal is to the right , dorsal is
to the top. ( j ) Distal is to the bottom. Reprinted from Dawson et al. [ 23 ]
5 Digit Regeneration in Mammals