Fig. 2. Barx2 (red) and collagen II (green) protein expression during limb development. At E11.0, Barx2 and collagen II are co-expressed in mesenchymal condensations (A,D). Barx2 expression precedes collagen II expression in the chondrogenic front (A, arrows). At E12.5, Barx2 and collagen II continue to be expressed along the developing digit. Barx2 expression is upregulated in the cell layer marking the joint interzone (B,E), whereas collagen II expression is downregulated in the developing joint. Barx2 and collagen II are co-expressed in the developing articular cartilage of carpal (C) and phalangeal (F) joints in newborn mice. (D) A higher magnification of A. (E) A higher magnification of B.