Regeneration of rat tracheal epithelium: changes in gap junctions during specific phases of the cell cycle.

Uninjured mitotically inactive tracheal epithelium has virtually no gap junctions. When the epithelium is stimulated to proliferate synchronously through a single wave of DNA synthesis and cell division, study of thin sections and freeze-fracture replicas by conventional transmission electron microscopy reveals that gap junctions are formed by the end of the DNA synthetic (S) phase. During the period of mitosis (M), the gap junctions disappear and are not again observed as the superficial cells undergo mucous and ciliary differentiation and normal pseudostratified architecture is restored. If the regenerative cells are continuously stimulated so they go through at least one additional S phase, gap junctions begin to reappear in G1 and reach peak numbers at the end of the second S phase. The correlation of the appearance of gap junctions in regenerating tracheal epithelium with a specific phase of the cell cycle and the absence of these junctions in cells in other phases of the cycle and in the differentiated progeny cells suggests that this surface feature plays a role in control of mitotic activity.