Histogenetic aspects of deer antler development.

Deer antlers are the only mammalian organs that, once lost, can fully grow back; therefore, they offer a unique opportunity for investigating the mechanism underlying mammalian organ regeneration. This review summarizes the current knowledge of antler histogenesis. The axis of a pedicle (antecedent of antler) and a first antler consists of an internal component and an external component. Formation of the internal component commences from the proliferation of antlerogenic periosteal cells and undergoes 4 ossification stages: Formation of the external component goes through 3 distinguishable stages. Antler velvet transformation is mainly associated with alteration in the skin appendages. Subsequent antler regeneration is divided into 5 stages. The present account, together with the companion paper on antler morphogenesis in this special issue (E4, 1836-1842), provides a foundation for further mechanistic study of this fascinating model for mammalian organ regeneration.