Figure 2.

Lubricin mRNA expression during elbow joint formation and in adult knee joints. (A) Pseudo-colored pictures showing Prg4 mRNA expression (red) and cell nuclei (blue) in the developing mouse elbow joint from E14.5–E17.5. Cavitation between the humerus and ulna begins at E14.5. Gdf5 is still strongly expressed in the presumptive joint mesenchyme, but Prg4 is not expressed at that time. Prg4 mRNA expression is detected at the forming joint surfaces from E15.5, after cavitation has begun, whereas Gdf5 expression is no longer detected in the joint area. Expression of Prg4 at the cartilage surfaces and adnexal structures increases further as maturation proceeds. (B) Pseudo-colored pictures showing Prg4 or Agc1 mRNA expression (red) and cell nuclei (blue) in 3-month-old (P90) and 6 month-old (P180) mouse knee joints. Alizarin red and Alcian blue–stained (A&A-stained) adjacent sections are included for orientation. Prg4 expression persists throughout adult life at the articular cartilage surface and within the synovium but is not detectable in the growth plate cartilage. Agc1 is expressed in articular and growth plate cartilage.