Genetic regulation of stem cell pluripotency (continued)

Embryonic stem cells (ESCs) have a so-called minimal phenotype and a minimum of receptors and programs for interacting with the microenvironment. It has been shown that only 5% of almost half a thousand genes responsible for transsignalization are expressed in proliferating ESCs. Deciphering the molecular mechanisms of stem cell pluripotency is one of the most "hot spots" of modern molecular and cellular biology. The list of genes involved in maintaining the state of pluripotency increases with each study, including both intracellular and surface markers. Thus, the study of gene expression in mouse embryonic stem cells in comparison with differentiated cells made it possible to isolate a specific ESG1 gene. Like OCT4, SOX2 and NANOG, the ESG1 gene plays an important role in establishing and maintaining a pluripotency state. Although the manifestation of all these genes is confined to the early stages of embryo development and the formation of germ cells, their expression profile is not identical to each other. For example, the initiation of the NANOG gene is observed during the formation of morula, while ESG1 is expressed throughout the pre-implantation period of embryo development. OCT4 expression also has its own distinctive features from ESG1. Further studies using the cDNA method showed that in developing primordial germ cells (primordial germ cells - PGC), these genes function at different times: In mice, ESG1 is specifically expressed at the stage of embryo preimplantation, in stem cells and primary germ cell lines. Functioning up to the stage of gonad formation, ESG1 is then turned off similarly to the OCT4 gene. In the culture of human embryonic stem cells, the co-expression of the ESG1, SOX2 and OCT4 genes occurs similarly, although there is no expression of ESG1 in some cell lines. These data indicate the existence of conservative regulation of pluripotency in mice and humans.

The important regulatory role of these genes has been demonstrated in experiments on reproductive and therapeutic cloning of mice. Reproductive cloning ends with the birth of animals like Dolly the sheep. In therapeutic cloning, the transplantation of somatic cell nuclei into an anucleated egg and the subsequent growth of the embryo is carried out only for the purpose of obtaining individual stem cells. During the study, scientists tested mouse embryos for the presence of the OCT4 gene. If OCT4 activity was detected in the embryo, it meant that the changes necessary for the formation of the embryo occurred in the donor nucleus, in which this activity was initially absent. Assessing the level of OCT4 activity, the researchers found that during cloning, only in 34% of cases, OCT4 activity is recorded in the necessary places of the embryo during the first (most important) days of development. Comparison of embryos obtained by cloning and in vitro fertilization showed that in the first case (during cloning) the level of OCT4 activity was significantly lower. The data obtained showed that testing clones for OCT4 activity in the early stages of development will help to select only viable embryos from which stem cells suitable for therapeutic use can be grown.

Another important characteristic of ESCs in culture is the virtually unlimited proliferation potential. Using knockout mouse lines, it was shown that this phenotypic feature occurs when three cytokines (LIF, SCF, IL-6) bind to a complex heterodimeric receptor and then transmit a signal with the participation of gp-130 and Stat-3 to a complex of genes controlling cell mitosis. At the same time, at the chromatin level, Stat-3 DNA interacts with the c-fos promoter.

In addition, in a study conducted by American scientists on the line of embryonic stem cells of Drosophila melanogaster, the participation of microRNA (microRNA) in the regulation of stem cell division was demonstrated. In mutants with impaired microRNA processing, cell division was delayed during the transition from the G1 stage to the S stage of the cell cycle. The authors believe that microRNA may be part of a mechanism that makes stem cells insensitive to external signals that normally stop cell division.

The elucidation of molecular genetic mechanisms for the preservation and maintenance of the individuality of stem cells is the key to the formation and development of regenerative medicine. Such discoveries will make it possible to find out the mechanisms of cell death and the development of various diseases. Ultimately, this will allow the development of targeted therapy methods for the restoration of damaged tissues and the treatment of various ailments.