Nexus formation in the myometrium during parturition and induced by estrogen

The occurence of nexuses (gap junctions) in mouse uterine smooth muscle was found to depend on the hormonal state. As revealed by freeze-fracture electron microscopy, nexuses are virtually absent in virginal and pregnant mice. Abundant, large-sized nexuses were observed in the myometrium during parturition. Estrogen application to virginal mice also induced an increase in number and size of nexuses. Our observations indicate that a new formation of nexuses occurs in differentiated cells. New nexuses may be formed by the confluence of nexus subunits preexisting in the cell membrane or by newly biosynthesized components.