Identifying and characterizing the joint cavity‐forming cell

AbstractFor many years, a large body of circumstantial evidence supported the notion that the synovial membrane produced the hyaluronan‐rich synovial fluid. A quantitative cytochemical technique for uridine‐diphospho glucose dehydrogenase (UDPGD) activity established that fibroblast‐like cells on the intimal surface of the synovial lining made a specific contribution to maintaining these glycosaminoglycan levels. Our studies have aimed to determine the mechanisms that control the attainment and persistence of this differentiated phenotype, and have recently focused on their appearance during joint cavity development in the embryonic limb; a process that is dependent upon skeletal movement. These in situ micro‐biochemical studies have shown that cells bordering the presumptive joint cavity exhibit raised UDPGD activity, are associated with a matrix rich in hyaluronan and show immobilization‐induced loss in such characteristics. Together with complimentary studies in adult joints, this suggests that mechanical stimuli promote the acquisition of this joint line‐forming phenotype. For this reason our studies have attempted to identify the ‘up‐stream’ mechano‐dependent factors that cont