β Scribed by Jerrold Fried
No coin nor oath required. For personal study only.
In estimating average generation times of proliferating cell populations by the grain-count halving method, one major source of error derives from the possibility that the daughters of lightly labeled dividing cells will have grain-counts below the counting threshold. This phenomenon will cause the observed mean or median grain-count of labeled cells to decrease too slowly, leading to an overestimate of the generation time (possibly by 30 ~o or more). To compensate for this effect, a method is proposed which provides, for each sample, an estimate of the number of such cells below the threshold, and which enables a corrected mean or median grain-count to be computed.
The method consists of deriving theoretical expressions for the interphase labeling index (assuming no threshold error) as a function of time; comparing the theoretical and observed labeling indices of each sample; and (assuming the former is larger than the latter) taking the difference to be proportional to the number of cells whose progenitors had fallen below the threshold at division.
The correction procedure, which requires knowledge of labeled percentages ofinterphase and mitotic cell samples, is derived for several commonly employed models. These include exponentially growing and steady-state systems, with or without cell loss. It is shown that, subject to a number of stated assumptions, the correction procedure is identical for all systems in which every cell has an equal loss probability (i.e. for this class of systems, the procedure is model-independent).
To illustrate the use of this method, it is applied to data from a study of acute human leukemia.
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