The measurement of the cell cycle time in squamous epithelium using the metaphase arrest technique with vincristine

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Abstract
In squamous epithelia with a single layer of germinative cells, the age distribution of cells in the cell cycle depends on the direction of the mitotic axis (i.e., a line joining the nuclei of daughter cells) relative to the plane of the basal layer. When axes are in the plane of the basal layer the age distribution is exponential; when cells divide at right angles to the plane of the basal layer, the age distribution is rectangular. When there is a ratio of vertical to horizontal axes, the age distribution is intermediate but can be calculated from knowledge of the proportion of axes in the plane of the layer. Squamous epithelia can be classified according to this arrangement of axes. When there are multiple layers of germinative cells, as in psoriasis, the age distribution is exponential to a good approximation, whatever the direction of the mitotic axes in the several layers. The importance of these observations is demonstrated by analyzing metaphase arrest experiments with vincristine in the single layer of germinative cells in the mouse esophagus, and in the several layers found in psoriatic epidermis. Choice of the wrong age distribution leads to an error of 6 h in the esophagus and 23 h in psoriatic epidermis, when the mean cell cycle time is calculated. In squamous epithelium, it is most important to know the age distribution before calculating the cell cycle time by methods involving measurement of the rate of entry of cells into mitosis or DNA synthesis.