What are haploid or diploid cells

Researchers are creating haploid stem cells for the first time

23 instead of 46: For the first time, researchers have succeeded in creating embryonic stem cells with just a single set of chromosomes. These cells are thus haploid, a property that otherwise only egg and sperm cells have. The big advantage: Because there is only one copy of each gene letter, it is easier to research the effects of mutations - or to trigger them, according to the researchers in the specialist journal “Nature”.

Our body cells normally have double the set of chromosomes, half of which comes from the mother and the other half from the father. This means that there are two copies of each gene. It is different in our germ cells, the egg cells and sperm. You only have 23 chromosomes, the simple set. Instead, these haploid cells cannot divide any further, instead they fuse during fertilization and thus create the diploid cells of a new embryo.

Embryonic stem cells obtained from fertilized egg cells are also diploid. Their double set of genetic material makes it difficult in some cases to locate mutations or to change the genome - because there is always a copy of the gene letter, which also plays a role in the effects.

"Half" set of chromosomes

Ido Sagi from the Hebrew University of Jerusalem and his colleagues have now succeeded for the first time in generating haploid embryonic stem cells. To do this, they use unfertilized human egg cells, which they use chemical triggers and a light electric shock to divide. From these cell divisions, mostly diploid stem cells emerged, but between which there were also haploid specimens.

In the body's cells we normally have 46 chromosomes - 23 pairs. © NIH

The researchers isolated these haploid embryonic stem cells and thus established a multiplying cell culture. As tests have shown, these stem cells with “half” the chromosome set are also pluripotent and thus have the ability to differentiate into all cell types and tissues.

Genetic life of its own

Interestingly, however, these stem cells are more than just half of the whole: their gene activity differs significantly from that of diploid stem cells, as the researchers report. Some genes are much more active, but the X chromosome is largely muted - as is otherwise only the case with male body cells. However, since these stem cells come from a woman, it should be active.

"These cells will provide research with a completely new tool to understand human development - and also the reasons why we reproduce sexually instead of parthenogenetically," explains senior author Nissim Benvenisty from the Hebrew University of Jerusalem. In addition, having only one copy of the gene at a time makes it easier to study the effects of mutations.

But the haploid stem cells could also be useful for gene therapy: "One of the greatest advantages of using haploid stem cells is that their genome is much easier to modify," explains Sagi. In the future, this could make it easier to repair harmful mutations using genetic engineering, for example, and it simplifies the cultivation of cell lines that are genetically absolutely identical. (Nature, 2016; doi: 10.1038 / nature17408)

(Columbia University Medical Center, March 17, 2016 - NPO)

17th March 2016