CONNEXIN-26, CONNEXIN-32 AND CONNEXIN-43 ARE EXPRESSED IN VIRGIN, PREGNANT AND LACTATING MAMMARY-GLANDS

Gap junctions (GJ) are formed by a number of homologous proteins terme d connexins. Here expression of connexins Cx26, Cx32 and Cx43, was eva luated by immunofluorescence (IF) in mammary glands from virgin, pregn ant and lactating rats. Cx26, Cx32 and Cx43 labeling was detected in e pithelial parenchymal cells at all functional stages. Cx26 and Cx32 la beling was very low in glands from virgin animals, somewhat greater in glands from pregnant animals and significantly higher (in number and size) in lactating animals. In the last ones, Cx26 and Cx32 punctate l abeling was localized to the basal and lateral membranes of alveolar e pithelial cells and collecting ductules. Cx43 punctate labeling was re stricted to the periphery of alveoli towards the basal pole of epithel ial cells at all functional stages, and it enlarged slightly during la ctation. At this localization, Cx43 may form GJ between myoepithelial cells and/or between epithelial and myoepithelial cells. Cx43 was also found to be steadily expressed in the connective tissue which surroun ds and invades each parenchymal lobe, at all functional stages. At thi s localization, Cx43 may couple fibroblasts and/or adipose cells. IF s tudies in sections from lactating mice showed the same distribution of connexins. Immunoblots confirmed specificity of labeling and the pres ence of Cx32 and Cx43 in the mammary gland. The increase in connexin e xpression detected during pregnancy and lactation may be important for epithelial cell differentiation and secretion in the mammary gland.