2023 Author: Bryan Walter | [email protected]. Last modified: 2023-05-21 22:24
In a culture of mammalian haploid cells (containing one set of chromosomes, shown in red), diploid cells are inevitably present (containing two sets of chromosomes, shown in green). Spanish researchers found that certain anti-cancer drugs can control the ratio of cells with different numbers of chromosome sets
Most cells in mammals (with the exception of sex cells) carry two sets of chromosomes and are called diploid. In them, each gene is represented by at least two copies - alleles, and alleles can differ from each other within the cell. This complicates the study of the functions of genes, since in this case, scientists must analyze the effects of several alleles at once and somehow separate them from each other.
Therefore, yeast cells are often used in genetic research. They are eukaryotes (their cells have nuclei), and most often they are haploid, that is, they have a single set of chromosomes. However, yeast is a fungus, that is, representatives of another kingdom, so the data obtained in experiments on them cannot be directly transferred to animals, including humans.
The first line of human haploid cells P1-55 appeared only in 1999. It comes from the cells of a male patient with chronic myeloid leukemia. Others followed, including HAP1. They always contain diploid cells, and over time there are more of them, since death mechanisms are activated in haploid cells, which are controlled by the p53 protein. Accordingly, it is necessary to somehow prevent or stop these processes so that the percentage of haploid cells in culture remains high for a longer time.
Researchers at the National Center for Cancer Research (Centro Nacional de Investigaciones Oncológicas, CNIO), led by Oscar Fernandez-Capetillo, used HAP1 cells to work out mechanisms for maintaining haploidy. Scientists acted on these cells with DAB, the precursor of the common cytostatic agent taxol, or nocodazole or paclitaxel (also cytostatics). These substances were chosen as the most promising in the screening of 1000 potential candidates. Means of this class do not kill cells, but disrupt their division. Usually, these drugs act on components of the cytoskeleton - microscopic strands of tubulin protein, which help to first align chromosomes along the equator of a dividing cell, and then pull them apart to different poles.
Under the action of cytostatics, HAP1 diploid cells practically stopped dividing, while haploid cells continued to do so. DAB worked most effectively. To find out if this drug works only on this line, scientists tested it on diploid cells of another species - mouse embryonic fibroblasts (MEF). They tend to spontaneously tetraploidize - the formation of cells with four sets of chromosomes. Under the influence of DAB, the proportion of tetraploid cells among fibroblasts decreased. This means that the drug, in principle, allows you to reduce the "average ploidy" in various cell cultures.
On the left - haploid cells that are actively dividing, on the right - diploid cells in which division is impaired. Tubulin is blue, phosphorylated histone H3 is red, and centromere marker is green.
The state of cells with a different number of chromosome sets after the application of various cytostatics and the proportion of these cells in culture
The discovery is useful not only for geneticists, but also for oncologists, the authors of the study note. The cytostatics used in it belong to taxanes. It turns out that taxanes in certain doses (low enough were used in the work) can remove cells with an abnormally high number of chromosome sets from tumors - and such cells are found in 7 percent of cancers. The main author of the article, Oscar Fernández-Capetilo, comments: "The results of the study may help to identify cancer patients for whom treatment with taxol and other taxanes will be especially effective."
Haploid somatic cells do not necessarily have a neoplastic origin. In 2016, Israeli and British researchers created two lines of human embryonic stem cells that carry a single set of chromosomes. Embryonic stem cells divide indefinitely, but normally do not carry the mutations characteristic of cancer cells.