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the myth of the chimera

In Greek mythology, Chimera (Χίμαιρα / Chímaira: "fabulous animal"; in Latin, Chimæra) is a hybrid monster generally considered to be the daughter of Typhon and Echidna, although for the poet Hesiod the mother of the Chimera is designated by a pronoun that can refer to both Echidna and the Hydra of Lerna. The chimera roamed the regions of Asia Minor, terrorizing populations and devouring animals, and even entire herds. It is possible that the Sphinx and the Nemean Lion were born from her union with Orthro.

Chimera was finally defeated by Bellerophon with the help of Pegasus, the winged horse, under the command of King Ióbates of Lycia. There are various descriptions of her death: some simply say that Bellerophon pierced her with his spear, while others maintain that he killed her by covering the tip of the spear with lead that melted when exposed to the Chimera's fiery breath.

interpretation of the chimera

"The chimera is a very complex symbol of imaginary creations from the depths of the unconscious, which perhaps represent unsatisfied desires, sources of frustration and subsequent pain. The chimera is seen as a monster that seduces and loses those who approach it, a monster that cannot be fought head-on and that must be pursued to catch it in its deepest lairs"
one of the many interpretations that can be given to the chimera. Everyone can see the chimera however they want: A wish, a curse, something purer or even like rebirth and becoming a great combination of fantastic things. It is each person's task to decide what their interpretation of said creature is...

What creatures fall into the category of chimera? (these are just a few, but any hybrid can fall into this category.)

• Basilisk
• Faucet
• Hippogryph
• Harpy
• Mermaids
• Winged horse

chimeras in biology and the real animal world

In biology we also use the term chimera, to refer to those animals that we have generated by mixing embryonic cells from two different individuals, generally from the same species, although they can also be from different species. In biology things are a little more complicated than in mythology... after mixing embryonic cells derived from pigmented mice and albino mice. In the resulting embryo, each group of cells gives rise to different parts of the body, with different pigmentation, as can be seen with the mottled pigmentation and the presence of one pigmented eye (derived from the pigmented embryonic cells) and the other albino eye. (derived from albino embryonic cells). Due to their appearance, these mouse chimeras are also often called mosaics. Although the use of the word mosaic is usually restricted to transgenic organisms, the presence of different genotypes or genetic modifications in the same individual, or the coexistence of genetically modified and unmodified cells in the same organism. Biological chimerism is much less precise than sculptural chimerism. Mice are not born that have half their bodies black and the other half white, clearly defined and separated, like sphinxes. Biology is always more complex than the imagination of sculptor artists.

Interspecific chimeras, with embryonic cells from different species, are logically much more difficult to produce. They have been an exciting challenge for many biologists for years. Great biologists mixed embryonic cells from different species to solve basic questions about the initial development of the animals they investigated. In 1975, Nicole Le Douarin mixed cells from chicken and quail embryos to investigate the initial events in the development and cellular differentiation of a vertebrate. Richard Gardner, also in 1975, mixed cells from mouse and rat embryos to study the early stages of preimplantation development of a mammalian embryo. In both cases, the researchers used cells from different species as markers, so they could track them once they intermingled, forming the resulting chimeric embryo, which never progressed to term.

In 1984, studies were done mixing sheep and goat embryonic cells. These pioneering studies were followed by many attempts, in vitro, in the laboratory, mixing embryos from many more or less related species, generally with limited success.

The first great success in the field of interspecific chimeras was obtained by the laboratory of Hiromitsu Nakauchi, from the University of Tsukuba (Japan) with his article published in the scientific journal Cell in 2010. In that seminal article he demonstrated three types of experiments, represented in the accompanying figure: (1) It was capable of generating intraspecific mouse chimeras by mixing embryonic cells from mice deficient in the Pdx1 gene (mutants for this function, necessary to develop the pancreas) with embryonic cells from wild mice, and the latter were responsible for to develop the pancreas that the former were incapable of producing; (2) they mixed rat and mouse embryonic cells, using both species as the recipient embryo (as blastocyst), and in both cases they obtained viable animals, that is, chimeric rats with mouse cells, and chimeric mice with rat cells; (3) Finally, the experiment that catapulted them to fame was the use of Pdx1-deficient embryos that were injected with wild rat embryonic cells, and the latter (from rats) were able to support the development of a rat pancreas. in a mouse body.

Are human chimeras possible?

Early attempts with non-human primate embryonic cells inside developing mouse embryos were not very successful. The chimeric embryos progressed a few divisions but did not implant or continue normal uterine development. Many laboratories tried, unsuccessfully, to reproduce the results of Nakauchi's group, experiments that were technically very advanced and complicated to replicate. This same laboratory demonstrated in 2015 that chimeric embryos resulting from mouse embryos injected with pluripotent human embryonic cells were unable to colonize the resulting mouse embryo.
The next experiment that we learned about, the result of collaboration between various laboratories, and coordinated by Juan Carlos Izpisúa-Belmonte, a Spanish researcher at the Salk Institute in La Jolla, San Diego (California, USA), provided some preliminary results, not entirely successful but certainly surprising, about the possibility of generating interspecific chimeras that involved human cells. The study was published in the journal Cell in 2017. As summarized in the attached figure, essentially three types of experiments were addressed: (1) Nakauchi's initial experiment was reproduced, with these authors also being able to generate chimeric mice with cells of rat; (2) rat embryonic cells were unable to colonize and intermix to form interspecific chimeras with developing pig embryos; and (3) they managed for the first time for a few human embryonic cells to colonize some organs of a developing pig embryo.

If we mix human embryonic cells into a developing pig embryo: (1) What do we call the resulting animal?; (2) What percentage of human cells must an animal have to be considered human?; (3) When does that animal stop being a pig and start being a human being?; (4) Is it ethically acceptable to generate these animals for possible use in regenerative medicine?; (5) Is the risk justified by creating these chimeras between humans and pigs for therapeutic and medical purposes?

Obviously the research team also had to consider all these ethical dilemmas, especially in order to obtain the corresponding permits from the Animal Experimentation Ethics Committees, mandatory to be able to undertake these experiments, under very limited conditions. In particular, the researchers stopped the gestation of the few chimeric pig embryos with human cells that they obtained at 3-4 weeks of fetal development (the pig has a normal gestation of 3 months, 3 weeks and 3 days), just before The central nervous system will begin to develop, to prevent any human cell from colonizing the brain of the developing chimeric animal. The experiment generated controversy and controversy. Far from obtaining a result similar to what the Japanese researchers had obtained in their rat/mouse chimeras, here it did not seem possible that a single pig organ could be obtained essentially from human cells. Only a few human cells were visualized (one human for every hundred thousand pigs), distributed in different parts of the developing pig embryo. Once again it was not a typical sculptural chimera, once again biology reminded us of its complexity.

These experiments are interesting from the perspective of developmental biology, to learn how embryonic cells differentiate to give all the multiple types of cells that make up our organs. But they are unlikely to result in chimeric animals that we will be able to use as a factory for spare human organs. Each human organ is made up of many types of cells: muscle cells, blood vessels, nerves, connective tissue, parenchyma, etc. It is currently very difficult to imagine that each and every one of these tissues would derive from a single embryonic origin (for example, from human embryonic cells). The organs were most likely as chimeric as the animal itself, with human parts and parts of the other species used to create the chimera. And, of course, then these chimeric organs could not be used in transplants, given that the non-human part would be immediately detected as foreign by the immune system of the transplanted patient and the organ would be suddenly rejected.

Will these chimeras have human consciousness? What rights will these chimeras have? Those of any animal or should we also grant them rights as human beings, even partially? It would also be possible, in theory, for these human cells to colonize the reproductive system of the chimeric animal. Then this chimera would be capable of generating human sperm or eggs, which would open other dilemmas in relation to the possible use of these gametes and their consideration as animal or human biological material.

" These questions may seem ridiculous and even too risky, but I sincerely believe that we will have to face an ethical debate that allows us to properly evaluate and manage these experiments and their foreseeable consequences, before carrying them out. And this is no longer science fiction. It's equally fascinating and worrying science..."

With this reflection the original text end,I decided to include almost this entire part since the topic of chimerism in biology seemed quite interesting to me... I leave that final opinion of the author since I agree in a certain way. Although I speak from my ignorance, I find fascinating the fact that real chimeras can be created in the future... Although I wouldn't want to see it. It would be something horrible, but at the same time wonderful. Or so I feel... For now, I leave my preference for the subject only in the fantasy and unreal, I don't really want to get back into the biological after this short investigation.