24 March 2017

All cells are equal, but some are more equal

The first mutations occurring in the human body have been studied

Anna Stavina, XX2 century, based on ScienceDaily: First mutations in human life discovered

Scientists have managed to track the first mutations occurring in the human body. Specialists from the Sanger Institute of the Wellcome Trust Foundation (Wellcome Trust Sanger Institute), together with colleagues from other institutions, analyzed the genome of adult cells and "looked" back in time, thereby investigating the process of embryo development.

The results of the study were published in Nature (Ju et al., Somatic mutations reveal asymmetric cellular dynamics in the early human embryo). Scientists have found that after the first division of a fertilized egg, one of the cells becomes dominant. Subsequently, in an adult organism, more descendant cells of this dominant cell are found than descendants of the second cell.

Researchers have long been interested in the question of what happens in the early stages of human embryogenesis. However, it was not possible to find an answer to it with the help of direct study. In the course of the new work, scientists analyzed the genome of cells obtained from blood samples of 279 volunteers suffering from breast cancer. As a result, it was possible to detect 163 mutations that occurred in the early stages of embryonic development of the organisms of the study participants.

Then the researchers used mutations that occurred at the stage of the first, second and third division of the fertilized egg to find out in what ratio the descendants of the first two cells of the embryo are present in the adult body. It turned out that the first of the dominant cells becomes the ancestor of 70% of tissues, while the second – only 30%. Similarly, the cells-descendants of those cells that arose as a result of the second and third division of the zygote were distributed.

A drawing from an article in Nature – VM.

Healthy cells from breast cancer patients were used for the study, but scientists also had the opportunity to analyze cells from removed tumors. If healthy tissues consist of several types of somatic cells, which are clones of various progenitor cells, then the tumor tissue consists entirely of descendants of a single cell. Thus, mutations that have arisen at the embryo level can either be present in all tumor cells, or absent in them – also in all. This served as proof of the hypothesis that the identified mutations actually occur in the embryonic period of development.

Dr. Young Seok-ju, the first author of the study, noted: "For the first time, we were able to identify mutations that occur at the earliest stages of human development. The process was like searching for a needle in a haystack, because there are much fewer such mutations than inherited genetic variations. By tracking them, we were able to figure out what happens during embryogenesis."

During the work, scientists also managed to determine the number of mutations that occur during the first three divisions of the zygote. The authors of previous studies believed that there is one mutation per division. However, according to the results of the new work, three new mutations appear in each daughter cell.

Professor Mike Stratton, head of the study and director of the Sanger Institute, explains: "This is a significant step forward in terms of increasing the volume of valuable information obtained through genome sequencing and mutation research. In reality, these mutations are archaeological traces of embryonic development preserved in the tissues of an adult organism. Therefore, when we find and study them, we will better understand human embryogenesis."

Portal "Eternal youth" http://vechnayamolodost.ru  24.03.2017

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