Dramatic Changes in Gap Junction Expression in the Mammary Gland During Pregnancy, Lactation and Involution

Abstract

Gap junctions constitute a widespread mechanism for intercellular communication. They are formed by a family of highly conserved connexin proteins which produce channels between adjacent cells permeable to molecules of approximately < lkDa. Gap junctions are presumed to be important in the regulation of embryonic development, growth and tissue differentiation via ionic and second messenger molecules. In electrically excitable tissues e.g. cardiac muscle, they facilitate the propagation of electrical currents (Bennett et al., 1991). Expression of gap junctions is developmentally and metabolically regulated, as seen in the uterus where there is a large increase in the levels of myometrial connexin43 immediately prior to parturition (Garfield et al., 1977). The mechanisms regulating gap junction expression remain unclear. In mouse mammary gland, gap junctions have been reported by freeze-fracture electron microscopy (Pitelka et al.,1973). Study of gap junctions has recently been facilitated by production of a range of site-directed anti-connexin antibodies (Evans et al., 1992). Using a panel of these antibodies, expression of connexins in mammary tissue has been investigated during pregnancy, lactation and involution.