Connexin expression and gap junctions in the mammary gland.

Gap junctional communication plays a vital role in embryogenesis, cell differentiation and the co-ordination of tissue responses. Gap junctions are formed by a family of closely-related proteins called connexins which show tissue-specific patterns of expression. The role of gap junctions in the mammary gland remains unclear. The lumena of mammary gland ducts are lined by luminal cells with an outer layer of basal cells. In rodents, the luminal cells express connexin26 only during pregnancy and lactation and the basal cells, in some reports, express connexin43. In the normal human breast the basal cells express connexin43, although human mammary epithelial cells in vitro have been reported to express both connexin26 and connexin43. Analysis of connexin expression at the molecular level is now bringing new insights into the structure and function of gap junctions in a range of normal and pathological cell systems.