Overview. Until quite recently, only one mammalian family of gap junction genes had been identified, namely, the connexins. However, a novel family of mammalian gap junction genes with low sequence similarity to the invertebrate gap junctions, innexins (Inxs), has been discovered in chordates and termed pannexins (Panxs). Currently, three pannexin members (Papanicolaou test, Panx2, and Panx3) have been identified in vertebrates. Previous studies on Inx mutants in Drosophilahave demonstrated Inx-specific functions including synaptogenesis in the giant fiber system, epithelial organization and morphogenesis, and germ cell differentiation processes. The role of pannexins in mammalian cells and tissues has yet to be...