Ciliated cell differentiation in regenerating rat tracheal epithelium

We studied the differentiation of progeny of mitotic cells in regenerating tracheal epithelium using a model of minimal mechanical injury in which the mitotic cells cycle only once and synchronously. Ultrastructural features of cells which incorporated tritiated thymidine were assessed at a series of times after DNA synthetic phases. Cells arising from G₁ arrested populations and G₂ arrested population were followed separately. The G₁ blocked cells were labelled at 22 hours after injury, divided at 32 hours and then differentiated. G₂ blocked cells were labelled at 39 hours after injury and differentiated without an intervening mitosis. Both populations exhibit initial differentiation of most superficial cells as secretory cells with a subsequent increase in ciliated cells and a reciprocal decrease in secretory cells. Transitional forms in which there are both secretory granules and developing cilia are seen among the labelled cells during the period of increasing ciliated cells. While it is probable that ciliated cells also arise from basal cells or directly from cycling cells, this study demonstrates that post mitotic redifferentiation of secretory cells is one source of ciliated cells in regenerating tracheal epithelium.