Expression of types II, VI and X collagen in equine growth cartilage during development

The synthesis and expression of collagen types II, VI and X were investigated in growth cartilage selected from a group of 31 horses and ponies in the age range 157 days of gestation to 12 years. Collagen isolation, immunolocalisation and in situ hybridisation techniques were used in order to provide information on the pattern of synthesis of these 3 collagens during endochondral ossification in normal horses. Type II collagen immunoreactivity and mRNA expression was found in each of the 3 zones of growth cartilage chondrocytes in all samples studied, whereas the localisation of both collagen types VI and X varied during cartilage development. Type VI collagen in the fetus was present only in the resting and upper proliferative zones and around the cartilage canal blood vessels in both articular/epiphyseal and metaphyseal cartilage, whereas in animals age >2 years it was present throughout all the cartilage studied. Type X collagen immunoreactivity and mRNA expression was detected only in the late hypertrophic zone in articular/epiphyseal cartilage in animals age <6 months and in metaphyseal cartilage in animals <12 months. These results demonstrated the presence of collagen types VI and X in equine cartilage for the first time. In addition, the pattern of expression of type II mRNA in the cartilage has been established and type VI and X collagens have been shown to differ in their expression during development of the skeleton.