Biological roles of gap junction proteins in cartilage and bone development

Cell-cell and cell-matrix interactions are essential for cell differentiation, function, and maintenance of skeletal tissue. Gap junction proteins, composed of connexin (Cx) and pannexin (Panx) families, mediate these interactions and play an important role in cell-cell communications. Cx and Panx share similar protein structures, but have evolved differently. The Panx family was initially identified by its sequence homology to the invertebrate gap junction innexin family. The Panx family comprises three members, Panx1, 2, and 3. Panx1 is expressed in many organs, such as the eyes, thyroid, prostate, kidneys, and liver, but its expression is especially strong in the central nervous system. Similarly, Panx2 is expressed mainly in the central nervous system. Panx3 is expressed predominantly in skeletal tissues, including cartilage and bone. In this review, we describe the expression and functions of Cxs and Panx3 in cartilage and bone.