Unit of Genetics and Gene Transfer, Core Research Laboratory, Istituto Toscano Tumori, Firenze, Italy.
Mutat Res. 2010 Jul-Sep;705(1):3-10. doi: 10.1016/j.mrrev.2009.12.004. Epub 2009 Dec 24.
Mutations are an inherent risk of cell duplication. On one hand, inheritable mutations are the driving force of biological evolution; on the other hand, their accumulation in somatic cells plays a key role in the development of cancer. The frequency of mutants (f) and the rate of mutation (mu) are biological features of any cell population: their measurement could provide important information about the risk of oncogenesis and the exposure to carcinogenic agents. However, the measurement of these parameters is not trivial. To measure f and mu, a potential sentinel gene is the PIG-A gene, which encodes one of the subunits of an enzyme essential in the biosynthesis of glycosylphosphatidylinositol (GPI). Since PIG-A is X-linked, mutational inactivation of the one single copy active in somatic cells entails absence from the cell surface of all the proteins that require GPI for attachment to the membrane: thus, mutant cells display a GPI-negative surface phenotype that can be easily detected by flow cytometry. The measurement of PIG-A mutants by counting cells with the GPI-negative phenotype has proved to be effective to measure mutant frequency in peripheral blood cells of humans and of others animals. Up to now, mu has been exceedingly difficult to measure in human cells; however, by using as a sentinel the PIG-A gene in lymphoblastoid cell lines we now have a test that makes it practical to measure mu in human cells.
突变是细胞复制的固有风险。一方面，可遗传的突变是生物进化的驱动力；另一方面，它们在体细胞中的积累在癌症的发展中起着关键作用。突变体的频率（f）和突变率（mu）是任何细胞群体的生物学特征：它们的测量可以提供关于致癌风险和致癌剂暴露的重要信息。然而，这些参数的测量并不简单。为了测量 f 和 mu，可以选择 PIG-A 基因作为潜在的监测基因，该基因编码糖基磷脂酰肌醇（GPI）生物合成中必需的酶的一个亚基。由于 PIG-A 是 X 连锁的，体细胞中单个活性拷贝的突变失活会导致所有需要 GPI 连接到膜上的蛋白质从细胞表面缺失：因此，突变细胞表现出 GPI 阴性的表面表型，这可以通过流式细胞术轻松检测到。通过计数具有 GPI 阴性表型的细胞来测量 PIG-A 突变体，已被证明可有效测量人类和其他动物外周血细胞中的突变频率。到目前为止，在人类细胞中测量 mu 非常困难；然而，通过在淋巴母细胞系中使用 PIG-A 基因作为监测基因，我们现在有了一种实用的方法来测量人类细胞中的 mu。
