The totipotentiality or totipotency is the ability, capacity and potential that each embryonic cell possesses to produce the total number of cells of an individual. The term derives from the Latin word totipotentia, which means ability for all things and / or ability to become or give rise to a complete organism.
The totipotent cells best defined or studied are the zygote and spores. Some authors use the term stem cells and totipotent cells as a synonym, but nevertheless there is no consensus on this aspect.
Stem cells, according to some authors, are groups of undifferentiated cells that can become different groups or types of specialized cells. They can be unipotent, multipotent and also totipotent. Only the latter are capable of giving rise to a complete individual.
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The father of totipotentiality is the German biologist and philosopher Hans Adolf Eduard Driesch. This scientist revolutionized the understanding of embryology thanks to his experiments with sea urchins.
In 1891 Driesch carried out experiments with two-celled (two-cell) embryos of the sea urchin. Echinus microtuberculatus (currently known as Psammechinus microtuberculatus) challenging the accepted hypotheses of the time about embryonic development.
Their results showed that the cells of an early embryo (zygote) when they are separated, either mechanically or naturally, could continue to develop until they form normal larvae, concluding that these cells are totipotent in their early stages of development..
This was in contrast to the results of Wilhelm Roux (pioneer of experimental embryology), who had worked with two-celled frog eggs. Roux found that killing one of the two cells developed malformed embryos, concluding that embryonic cells have predetermined destinations.
Later in 1910, the American chemist, zoologist and physiologist Jesse Francis McClendon would verify that Driesch's results could be replicated in frogs, chickens, other hedgehogs and even mammals..
Totipotentiality is characterized by the potential of some cells to give rise to a complete individual. These are capable of becoming any type of cell in the body and also in other extra-embryonic tissue.
Totipotent cells are formed in organisms of both sexual and asexual reproduction, they are zygotes or spores. They can be a zygote in the seed of a phanerogam (plant), in an egg of any animal, or in a uterus of a mammal (such as humans, elephants or mice).
This potential in most cases has a short period of existence during development. In the human body they have a limited time, approximately 4 days after fertilization. In other organisms such as plants, marine sponges, annelid worms, starfish and mice they have different duration.
In plants and fungi that reproduce by spores, it is said that these cells that do not need fertilization are of the totipotent type, since the zygote of these organisms has the capacity to produce all the types of cells required to develop a complete individual..
Numerous development, growth, and tissue culture studies in plants have repeatedly shown that many plant cells are totipotent. An example of this are small tissue cultures or stem cuts that, when placed in growth media, are capable of giving rise to or regenerating a completely new individual..
As already mentioned before, the first study that demonstrated the existence of totipotent embryonic cells was carried out with sea urchins (echinoderms). Since then many studies have been carried out to replicate Driesch's experiment and in all of them the result is the same (the existence of totipotentiality).
Another case in echinoderms, but this time with starfish and starfish, is the ability of some species of these to regenerate a complete organism from a section or part of an arm (without portions of the central disk). This regeneration capacity is due to the presence of adult totipotent stem cells.
Tissue studies in porifers (sponges) reveal that these primitive organisms have large numbers of totipotent cells. This allows them to produce or obtain any type of cell they need and sometimes also to be able to regenerate a complete organism from a small portion of the body..
In vertebrates, totipotentiality studies are described in embryonic development; that is, the embryonic cells of vertebrates such as fish, reptiles, birds and mammals have a totipotent behavior similar to that of Driesch's hedgehogs..
Regardless of the type of reproduction (cross-fertilization, self-fertilization and also parthenogenesis) the cells present between the zygote and the morula (first segmentations of the zygote) have the ability to produce all types of cells and to organize them into a coherent bauplan (a complete organism ).
Much of the scientific community classifies totipotent cells according to their origin and potentiality. According to their origin they are classified into embryonic, fetal and adult, while according to their potentiality they are classified into the following groups.
Those that give rise to a complete individual.
They can form cells that will give rise to any embryonic lineage, but they do not give rise to a complete organism.
Those that can only give rise to cells of the same lineage or embryonic layer.
Specialized cells that have the ability to differentiate into a single cell type.
Studies with totipotent cells (in the broad sense of the classification according to their potential) allow us to see them as a possible cure for many diseases, tissue regeneration, cell therapies and even potential sources for the cloning of plants, animals and the human being himself. which has been the subject of much ethical debate.
Studies of congenital diseases and cancer are approached by expert scientists in totipotent cells, due to the development and cell multiplication present in some of these diseases.
The analysis and studies of the first zygotic divisions (of totipotent cells) have provided a lot of knowledge about the activation and inactivation of genes and also about the involvement of proteins that make this process possible.
Other scientific advances related to studies of the first embryonic or zygotic divisions are malformations and / or birth defects caused by abnormal early cell divisions and differentiation..
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