A book entitled The Master Builder: How the New Science of the Cell is Rewriting the Story of Life, authored by Alfonso Martínez, has recently been published. Arias, research professor in the department of Medicine and Life Sciences at Pompeu Fabra University in Barcelona (Spain). Previously, Martínez Arias taught Developmental Mechanics at the Department of Genetics at the University of Cambridge. The author tries to draw attention to the development of multicellular animals and their evolution, and wants us to understand it in a deeper way. To this end, he tries to get us to leave aside a way of seeing things centered on genes and focus on the study of cellular behavior. Therefore, at the beginning of his book, he asserts that “geneticists have been so successful in finding changes in genes associated with dysfunction that we have fallen into the trap of equating correlation with causation.”
The author divides the publication into three parts. In the first, he maintains that cells actively use genes to send messages and guide the formation of relevant structures. The second part refers to the fabulous behaviors of cells in gastrulation and specifically the “choreography” by which embryos establish their axes and body planes. The third part illustrates the discovery of what he calls a new type of “creature”: the gastruloids, as a means for new research that helps understand the evolution and development of organisms.
In his publication, Martínez Arias is going to replace the “model” analogy usually referred to genes and DNA with another that he calls “hardware catalog.” In such a way that the genome would be more like the inventory from which the cell would order the necessary tools and proteins. He insists that it is cells that use genes to form complex three-dimensional structures, and emphasizes that genes do not perceive time or space. At the same time, he recognizes that cellular movements during gastrulation are currently inexplicable and striking.
Subsequently, he delves into the manifestations of cellular responses to various things such as their hardness, number, softness, physical substrate, order of events, density and number of adjacent cells. All this, at the same time that they have access to the “catalog” of genes that can be used for complex constructions. The clearest manifestation of this is the incredible activity of neural crest cells.
Later, he lists the difficulties researchers have in understanding the circumstances that promote the formation of what he calls small “creatures,” gastruloids, which have predictable topography and morphology. According to the author, they are not embryos, nor do they constitute a specific stage of their development, nor will they complete it. For him, they make up an “outline” of the basic pattern of bilateral organization of a vertebrate. By studying them in the laboratory, you can know the cellular interactions that occur and those that should occur so as not to hinder their development. That is why they have enormous value for researchers and, currently, do not present the legal obstacles that affect human embryos.
Regarding evolution, Martínez Arias considers that his vision coincides, since he considers that the appearance of multicellularity is the moment in which genes, which until then had been used as “simple” tools in unicellular organisms, with adequate responses to certain opportunities or environmental conditions begin to be used in cellular interactions. It is then the cells that use the genetic products as signals to reach unsuspected limits of complexity. The author thinks that these “conversations” between cells are the cause of gastrulation movements and animal body patterns that surely would have occurred in the Cambrian period.
The Master Builder finds it difficult to describe what happens inside and between cells as embryonic development progresses. The author, in some way, personalizes the cells, attributing to them powers such as “choose” and “decide” when they require some appropriate instrument or product from the genomic inventory and subsequently use it to achieve a necessary purpose. Logically, in that case, we would have to admit a consciousness in the cells or another explanation unknown to us. The responses of a cell to the different particularities of the environment: be it the physicochemical characteristics of the substrate, or the density, type or number of the cells that surround it, activate specific responses. However, this does not mean that there is a “choice” by the cell, but rather it is a simple reaction. Martinez Arias admits that we do not know the mechanism of cellular interactions, but at the same time he does not accept the theory of intelligent design. He simply states that we are in the initial phase that would lead us to discover the way in which cells together make a multicellular organism. For this purpose, gastruloids raise many questions that we had not asked ourselves until now.
Although reading the book may be exciting for those interested in these biological topics due to the novelty of the approach, it is worth making some observations from science and bioethics. Dawkins in “The Selfish Gene” attributed evolution to genes when he said: “We are survival machines, automated vehicles programmed blindly in order to preserve the selfish molecules known as genes.” Now Martínez Arias gives the spotlight to cells and in them would be the explanation of the formation and development of multicellular living beings and specifically also of human beings.
It is worth highlighting that both the genome taken in isolation and the cells, a vital unit, as well as all the components of the human organism that interact precisely, have important roles in its development, but none of them separately, neither the DNA nor the cells by themselves, explain the formation of a man or a woman. This does not mean that an organism with human DNA cannot be attributed an identity. Of course, it is not enough to verify that we are dealing with a cell with human DNA to know if we are dealing with a human living being, but we must also verify that it is an organism that begins as unicellular, then bicellular, then tricellular because a cell divides before the other, until the embryo, the fetus, the child, etc. is formed by mitosis.
In reality, experimental sciences can explain how, the functioning of a living organism, but they cannot explain why. This is what philosophy is for. What does not seem correct is to deny from experimental science the meaning, the purpose of the different organs and the living being in which they develop.
On the other hand, it is worth remembering that, from embryology, it has been confirmed that the body axes of the human organism are not configured from 20 days, but already in the fertilization of the oocyte, as stated in the article by Helen Pearson.
Finally, “gastruloids”, embryoids formed from embryonic stem cells or induced pluripotent cells (iPS), present ethical problems since, in the first case, by extracting embryonic cells, we end the life of the human embryo. In the second case, it is also possible to form a human embryo with iPS cells, so a similar difficulty could arise.
