CTSK and osteogenesis imperfecta: Further analyses on regeneration and skeletal development-related proteins revealed that Serpinh1b [Serpin peptidase inhibitor, clade H (heat shock protein 47), member 1b], a chaperone for procollagen and known risk gene for osteogenesis imperfecta (type X) (21), Cathepsin k (Ctsk, a bone catabolizing enzyme), and Osteonectin (Sparc) are enriched in 4 dpa/untreated fin regenerates, in agreement with previous reports (22, 23) (Figure 2A).