T. Szuwart et al., Ultrastructural aspects of cartilage formation, mineralization, and degeneration during primary antler growth in fallow deer (Dama dama), ANN ANATOMY, 180(6), 1998, pp. 501-510
Due to their rapid growth, regular replacement and easy accessibility, deer
antlers are considered a useful model for the study of cartilage and bone
differentiation and mineralization in mammals. The present study describes,
for the first time, the cellular and extracellular matrix changes associat
ed with cartilage formation, mineralization and degeneration in primary ant
lers on the ultrastructural level. Growing primary antlers of 3 to 4 cm len
gth were obtained from six fallow bucks, aged about 10 months. It was shown
that the chondroblasts were derived from progenitor cells of the antler pe
richondrium and differentiated into mature chondrocytes that subsequently u
nderwent hypertrophic changes. Concomitant with cell hypertrophy, formation
of a lacunar and a perilacunar extracellular matrix was observed, the latt
er containing numerous collagenous fibers. Mineralization of the extracellu
lar matrix occurred via matrix vesicles and the formation of apatite crysta
ls at distinct sites of the collagenous fibers. The hypertrophic chondrocyt
es of the mineralized cartilage then degenerated, a process that was also o
ccasionally observed in more distally located cells surrounded by still unm
ineralized matrix. No morphological indications of a transdifferentiation o
f hypertrophic chondrocytes into bone forming cells, i.e., co-occurrence of
a degenerating chondrocyte and a viable osteogenic cell in intact lacunae,
were found. The cellular and extracellular matrix changes seen in primary
antlers resemble those described for secondary antlers. Our results further
indicate that the hypertrophic chondrocytes of primary antlers eventually
undergo apoptosis, thereby providing further evidence that metaplastic conv
ersion of cartilage into bone does not play a role in antler growth.