Much less is known about how signaling pathways function during the subsequent maturation and maintenance of adult joint structures. Importantly, BMP signaling components are present in adult articular cartilage, suggesting that they may function during the late development or maintenance of this critical structure (Erlacher et al. 1998; Chubinskaya et al. 2000; Muehleman et al. 2002; Bau et al. 2002; Bobacz et al. 2003).