Differential expression of major gap junction proteins, connexins 26 and 32, in rat mammary glands during pregnancy and lactation

We examined the expression pattern of two major gap junction proteins, conn exin 26 (Cx26) and connexin 32 (Cx32), in rat mammary glands during pregnan cy and lactation. Immunohistochemically the two different Cxs were coexpres sed in acinar cells and were independently modulated according to the physi ological cell activity. Western blot analysis demonstrated that Cx26 gradua lly increased from early pregnancy, while Cx32 rapidly and dramatically inc reased at 16 h after parturition, and that both Cxs reached a maximum early in lactation. Increased expression of both Cxs was confirmed by Northern b lot analysis showing that their mRNA transcripts were significantly induced on the day of parturition. We also analyzed double-immunofluorescent stain ing for Cx26 and Cx32 on a confocal laser scanning microscope, in order to examine colocalization of these Cxs in situ. Cx26 immunoreactivity mostly o verlapped with Cx32-positive sites in acinar cells of lactating mammary gla nds, indicating that both Cxs were colocalized together in the same gap jun ctional plaques in lactation. These results suggest that upregulation of Cx 26 and Cx32 in acinar cells at lactating stages, with colocalization in the same gap junctional plaques, may be important for control of secretion by acinar cells in rat mammary glands.