Molecular biology and genetics of gap junction channels

Gap junctional communication between cells provides a mechanism for the movement of molecular information between cells via the unit of gap junction structure and function, the gap junctional channel. In the past five years, there has been rapid progress in identifying and characterizing a multigene family that is responsible for producing the gap junction polypeptides that are responsible for generating gap junctional channel oligomers between cells. The products of these genes have been referred to as connexins, and the multigene family can be categorized into two classes at present, the alpha class and the beta class. Members of these two classes can be distinguished on the basis of their primary sequence and overall predicted topological organization. The gap junction genes map to different chromosomes in both mice and humans, and these genes are utilized on a cell specific basis. Furthermore, these genes can be developmentally regulated, and multiple genes can be co-expressed simultaneously by the same cell type. Efforts to understand the precise structure-function relationship of the products of these different genes is now being approached by utilizing various expression systems. Criteria that can be used as a basis for determining membership in the multigene family is presented and discussed, as well as the rationale for using a nomenclature system for the gap junction multigene family that is based on genetic and structural relationships rather than the molecular size of the deduced protein products.