Mesenchymal dependent mode of cartilage growth in post-hatching birds

Cartilage growth depends on two types of resident cells; the chondrocytes and the perichondrial stem cells. Chondrocytes proliferation commits interstitial growth of cartilage while the appositional growth is driven by differentiation of the perichondrial stem cells. A third type of cartilage growth depending on mesenchymal cells has been recently described in the embryo. The current study aims to investigate the occurrence of mesenchymal-dependent cartilage growth in postembryonic life. We used samples of the oropharyngeal cartilage of both duck and goose in different ages. Mesenchymal-like cells were identified in the oropharyngeal cartilage of both duck and goose. They appeared spindle or flattened in shape with an oval nucleus and connected by cytoplasmic processes. Mesenchymal cells were observed in the cartilage of the middle nasal conchae, laryngeal cartilages of duck and arytenoid cartilage and entoglossal cartilage in the goose. Mesenchymal-like cells were organized as cellular streaks or as individual cells. Multiple areas of mesenchymal-like cells in the cartilage could be recognized. Mesenchymal-like cells are derived from the perichondrium. They undergo differentiation, acquired a spherical profile and were surrounded by the little amount of basophilic cartilage matrix. In conclusion, Mesenchymal-like cells contributed to the interstitial growth of the cartilage in the postembryonic period.