Fig. 1.
Synovial joint development in the mouse. Longitudinal views depicting key steps in the formation of the knee joint. a The first sign of a presumptive joint is a condensation of Col2 + limb bud progenitors at the presumptive joint site; b Joint specification is marked by induction of Gdf5 in the interzone and downregulation of Col2a1; c A joint space is formed by cavitation after progenitors for a variety of secondary joint structures are specified from the Gdf5 + progenitor pool; d Maturation of the synovial joint of the knee occurs during development and early postnatal life.
Reproduced from Salazar et al. [165], with permission