Trowbridge E A, Harley P J
Department of Medical Physics and Clinical Engineering, University of Sheffield, UK.
IMA J Math Appl Med Biol. 1988;5(1):45-63. doi: 10.1093/imammb/5.1.45.
Normally, cells reproduce by mitosis. In mammals, a system has evolved that is unique to cell biology. The circulating blood cells called platelets are produced from parent cells called megakaryocytes, but the mechanism of platelet production is not mitosis. At present, both the site and mechanism of production are still debated. This article describes a production mechanism based on a sequence of random binary divisions of the megakaryocyte cytoplasm as it traverses the pulmonary microcirculation. Using the measured megakaryocyte cytoplasmic volumes circulating in the blood of three different mammals, rat, rabbit, and man, a computer simulation of this process is developed. The simulation depends on two separate stochastic processes. The first involves the probability that a division of a cytoplasmic particle of a specified size will occur. The second relates to the relative sizes of the two particles produced by the binary division. These two processes are controlled by three parameters only: a lower threshold L on the platelet volume, below which the probability of a binary division is zero; a parameter lambda which defines the probability of division for volumes larger than this lower threshold; and the standard deviation S of the Gaussian distribution of possible volumes created by the binary division. A minimization scheme is used to establish those values of L, lambda, and S which provide the best fit to the experimental data obtained from the different mammals.
正常情况下，细胞通过有丝分裂进行繁殖。在哺乳动物中，进化出了一种细胞生物学特有的系统。被称为血小板的循环血细胞由被称为巨核细胞的母细胞产生，但血小板的产生机制并非有丝分裂。目前，血小板的产生部位和机制仍存在争议。本文描述了一种基于巨核细胞细胞质在穿过肺微循环时进行一系列随机二元分裂的产生机制。利用在三种不同哺乳动物（大鼠、兔子和人类）血液中循环的巨核细胞细胞质体积的测量数据，开发了该过程的计算机模拟。该模拟依赖于两个独立的随机过程。第一个过程涉及特定大小的细胞质颗粒发生分裂的概率。第二个过程与二元分裂产生的两个颗粒的相对大小有关。这两个过程仅由三个参数控制：血小板体积的下限阈值L，低于该阈值二元分裂的概率为零；定义大于此下限阈值的体积的分裂概率的参数λ；以及二元分裂产生的可能体积的高斯分布的标准差S。使用一种最小化方案来确定L、λ和S的值，这些值能与从不同哺乳动物获得的实验数据最佳拟合。
