The fusion of two sisters right into a single girl means that the id of the human being isn’t of their DNA | Science | EUROtoday

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Two eggs fertilized by two sperm coincided in a uterus and, as a substitute of giving rise to 2 sisters, they fused to type a single particular person: Karen Keegan. When she was 52 years outdated, this girl from Boston suffered very critical kidney failure, however fortunately she had three kids keen to donate a kidney to her. The docs did genetic checks to see which offspring was most suitable they usually obtained a serious shock: the check stated that two of them weren’t her kids. The actuality was much more astonishing: Karen Keegan had two totally different DNA sequences, two genomes, relying on the cell you checked out. Biologist Alfonso Martínez Arias maintains that this chimeric girl is conclusive proof that DNA doesn’t outline an individual's id.

The most inspiring science guide in historical past is The egocentric gene, in line with a survey carried out by the Royal Society of the United Kingdom. In this well-known work from 1976, the British biologist Richard Dawkins defended that the DNA molecule makes use of the human being as a mere envelope to be transmitted to the subsequent technology and be immortal. “We are survival machines, automated vehicles programmed blindly in order to preserve the selfish molecules known as genes,” Dawkins acknowledged. Almost half a century later, Martínez Arias refutes this angle of the egocentric gene and proposes a way more romantic different: the altruistic cell. “An organism is the work of cells. “Genes only provide the materials,” he states in The Master Builderan interesting and provocative guide from the London writer Basic Books that might be printed in Spanish in 2024 by Ediciones Paidós.

Martínez Arias, born in Madrid 68 years in the past, argues that the DNA sequence of a person isn’t an instruction guide or a development plan for his physique, however a field of instruments and supplies for the genuine architect of life: the cell. The biologist argues that there’s nothing within the DNA molecule that explains why the center is situated on the left, why there are 5 fingers on the hand or why twin brothers have totally different fingerprints. Cells are what “control time and space,” he proclaims. They are those who know the place proper and left are and the place precisely an individual's foot or an elephant's trunk ought to finish.

The biologist from Madrid spent 4 a long time on the University of Cambridge (United Kingdom), investigating how a solitary cell with a singular DNA sequence—the fertilized egg—is able to multiplying and changing into a person with billions of cells specialised in its duties. “The question often arises as to how it is possible that such similar genomes can build such different animals as flies, frogs, horses and humans. However, the real wonder is how the same genome can build structures as different as an eye and a lung in the same organism. Let's give the cells the credit they deserve,” says Martínez Arias, who in 2021 left his chair of Genetics at Cambridge to join the Pompeu Fabra University in Barcelona.

The first cloned cat (right) lost the orange color of the cat from which the DNA was copied (left).
The first cloned cat (right) lost the orange color of the cat from which the DNA was copied (left).Texas A&M University

The scientist remembers the global surprise after the birth of the first cloned cat, called Copy Cat, on December 22, 2001. Her DNA was identical to that of a cat of three colors – white, orange and black – but Copy Cat had the white and brindle fur. The two supposed clones looked nothing alike. The researchers had copied the genetic information from a cell that had the orange gene inactivated. The American company that intended to get rich by selling identical clones, Genetic Savings & Clone, had to close in 2006. “People didn't want a cat with the same genes as their pet, they wanted a cat that was exactly the same and behaved the same way.” the identical means,” emphasizes Martínez Arias. “That is simply impossible.”

The researcher uses a legendary phrase from his British colleague Lewis Wolpert (1929-2021): “The most important moment in your life is neither your birth, nor your marriage, nor your death, but gastrulation.” Martínez Arias compares this phase of embryonic development to a cellular dance with perfect choreography. About 14 days after a sperm and an egg come together, the resulting ball, of about 400 cells, will begin gastrulation: a dance that lasts six days and ends with the tiny sphere becoming the first sketch of the individual. In this new 20-day structure, the three axes of the future person are already distinguishable: left and right, up and down, belly and back.

The biologist Alfonso Martínez Arias, in a bookstore in London.
The biologist Alfonso Martínez Arias, in a bookstore in London.Jaime Marshall

These first days of pregnancy are an enigma, due to the obvious physical and ethical barriers to directly observing the process, but Martínez Arias' team in Cambridge overcame the difficulties in 2020 with an ingenious alternative. The Spaniard and his colleagues used a chemical cocktail to induce embryonic stem cells—derived from leftover embryos from fertility clinics—to form in the laboratory a three-dimensional structure similar to the result of gastrulation: a sketch of a person, but without the seed. of the brain or the tissues that would generate the placenta. His historic breakthrough was announced in the magazine Naturetemple of the best world science.

Martínez Arias believes that these structures that partially imitate the human embryo, called gastruloids, “unequivocally show that cells are the masters of construction, and that there is no blueprint in the genome to direct what they do.” The biologist marveled, for the first time in history, at something very similar to what happens in a mother's womb: that perfect choreography in which cells communicate with each other, through forces and chemical signals, and end up occupying their place as if they knew exactly what their destination was. “This ability to self-organize could be a fundamental property of cells,” hypothesizes the researcher, who cites the spectacular techniques of the French neurobiologist Alain Chédotal to visualize the cellular structure of embryos.

A 20-day-old human embryo (left) and a gastruloid.
A 20-day-old human embryo (left) and a gastruloid.Kathleen Kay Sulik

The Pompeu Fabra researcher remembers that his colleague Susanne van den Brink discovered that gastruloids were only formed if a specific number of cells were used: about 400. Cells know how to count. If the 400 are not there, the dance of gastrulation does not begin. They all have the same DNA molecule in their nucleus, but each cell reads only a few sections, specializing in certain tasks. That is why a brain cell will not look anything like another skin cell, despite having the same DNA and descending from the same fertilized egg. “Gastruloids are proof that a confederation of cells has the ability to work together, interpret signals from each other and the environment and choose which genes to use and when,” celebrates the biologist. “Genes are not our identity,” he repeats over and over again.

For Martínez Arias, the new science of the cell is rewriting the story of life. “We still don't know much about how cells are organized to use the genome, but the answers are out there, starting to manifest in our embryo-like cellular wonders or organoids. The century that is already underway is, and will be, the century of the cell,” he proclaims.

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