Morphological observation of antler regeneration in red deer (Cervus elaphus)

Abstract

Deer antler offers a unique opportunity to explore how nature solves the problem of mammalian appendage regeneration. Annual antler renewal is an example of epimorphic regeneration, which is known to take place through initial blastema formation. Detailed examination of the early process of antler regeneration, however, has thus far been lacking. Therefore, we conducted morphological observations on antler regeneration from naturally cast and artificially created pedicle/antler stumps. On the naturally cast pedicle stumps, early antler regeneration underwent four distinguishable stages (with the Chinese equivalent names): casting of previous hard antlers (oil lamp bowl), early wound healing (tiger eye), late wound healing and early regeneration (millstone), and formation of main beam and brown tine (small saddle). Overall, no cone-shaped regenerate, a common feature to blastema-based regeneration, was observed. Taken together with the examination on the sagittal plane of each regenerating stage sample, we found that there are considerable overlaps between late-stage wound healing and the establishment of posterior and anterior growth centers. Observation of antler regeneration from the artificially created stumps showed that the regeneration potential of antler remnants was significantly reduced compared with that of pedicle tissue. Interestingly, the distal portion of a pedicle stump had greater regeneration potential than the proximal region, although this differential potential may not be constitutive, but rather caused by whether or not pedicle antlerogenic tissue becomes closely associated with the enveloping skin at the cut plane. Antler formation could take place from the distal peripheral tissues of an antler/pedicle stump, without the obvious participation of the entire central bony portion. Overall, our morphological results do not support the notion that antler regeneration takes place through the initial formation of a blastema; rather, it may be a stem cell-based process.

Deer antler regeneration: Cells, concepts, and controversies

“…In more recent years, several authors hypothesized that antler regeneration is a stem-cell-based process and that these stem cells reside in the pedicle periosteum (Li and Suttie, 2001;Kierdorf et al, 2003;Li et al, 2004aLi et al, , 2005. Using various markers, different groups have since confirmed the presence of stem cells/progenitor cells in the pedicle periosteum as well as in primary and regenerating antlers (Cegielski et al, 2006;Li and Suttie, 2006;Mount et al, 2006b;Rolf et al, 2006).…”

“…Thus, in the roe deer splitting of the growth center normally occurs quite late, when the antler has already regenerated to a length of several centimeters. Li et al (2004a) further stated that wound healing during antler regeneration in red deer leads to the formation of a scar, which would not be compatible with blastema-based regeneration. However, the study by Bosch (2000) produced no evidence for the formation of scar tissue during casting-wound healing in the fallow deer.…”

“…Later, histological studies by Bosch (2000) and Kierdorf et al (2003) in fallow deer and of Li et al (2004aLi et al ( , 2005 in red deer suggested that antler regeneration does not involve dedifferentiation of cells of the internal pedicle tissues. Rather, as discussed already, there is evidence that the mesenchymal cells located at the growing tips of the regenerating antler are the derivatives of stem cells from a specific local source, viz.…”

“…Li et al (2004aLi et al ( , 2005 argued that, while in the early blastema of the regenerating urodele limb no distinct growth center can be identified, separate growth centers for the main beam and brow tine are established very early (before completion of wound healing) during antler regeneration. This observation holds for red deer, the species studied by Li et al (2004aLi et al ( , 2005, and also for some other deer species (e.g., fallow deer), in which the anlage of the brow tine develops very early during antler regeneration (Fig. 1b).…”

“…In each case, be it the fin of a fish, the limb of an amphibian, the tail of a lizard, or the antler of a deer, regeneration is made possible by the development of a blastema.'' More recently, the similarities and differences between the processes of antler regeneration in deer and limb regeneration in amphibians have been reanalyzed by different authors (Kierdorf et al, 1994;Bosch, 2000;Li et al, 2004aLi et al, , 2005Price et al, 2005a). The results of these studies are crucial to our understanding of what makes antler regeneration such a unique developmental event among mammals.…”