DNA is still the Master Key

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DNA is often identified with the “birth guide”, while “learning” is recognised as that which defines us later in life. But this is nothing more than a pervasive and persistent error. The reality is much more interesting than that. DNA is the way that growing up is recorded in our nature. British zoologist and writer Matt Ridley calls it nature via nurture, to nature through nurture, in a solvent paraphrase of the Galtonian dilemma. This is the key to understanding DNA as an object of controversy. Let’s take cancer, for example. They are not hereditary, but they are all genetic because they appear due to an accumulation of mutations in the DNA of our cells. Each of our neurons or our liver cells carries a copy of the whole human genome and it is thanks to that it can function properly. DNA is not only the vehicle of inheritance from parents to children, but also the operating manual of each of our cells throughout our lives. Cancer treatment is already benefiting from DNA technology, although genomic oncology is only in its infancy. The leaders of this discipline, like Bert Vogelstein, calculate that most tumors are due to the accumulation of half a dozen key mutations of the thousands that accumulate in any of our cells throughout the life, and in particular the cancerous ones. These mutations are distinct in each tumor type. In women with breast cancer, for example, it is already common practice to analyze their key genes, because it depends on the optimal treatment, whether modest chemo or a radical breast excision. This strategy is becoming widespread in other types of cancer, even though its results are poor. So, cancer is nature or parenting? It is both. We have all seen those photos of a family in which three generations of women have died of breast cancer. In this case, the inheritance is what weighs: the mutations with which those women were born were the cause of their fatal destiny. A more common case is that some mutation or another comes from birth and that the rest have been acquired during life, sometimes by carcinogenic factors such as tobacco smoke or ultraviolet radiation from sunlight. And at other times – many other times – by mere chance. This is an important concept worth dedicating a few more lines. Recent results from large cancer genomics projects show that one-third of the cancers that afflict the world are due to risky living habits such as smoking, burning on the beach or eating more than is strictly advisable in addition to the ingredients present in food products, among others.. But the remaining two-thirds are not the fault of the patient, but a product of chance. Since the ovum and the sperm become fertilized, our cells divide hundreds, thousands or tens of thousands of times, depending on what type they belong to. In each of these divisions, the entire genome has to be replicated, made up of 3 billion letters, and however precise the DNA replication system maya be, errors occur that propagate to the next cell generations. Two of every three cancers come from that chance. But whatever the source of a key mutation – or whoever is to blame for it – few scientists and doctors doubt that its detection is essential to decide the treatment. Unfortunately, most treatments still use techniques and products that enhance cancer growth as supposed to treating the root cause of it. DNA is nature and parenting or, as Ridley would say, nature by way of parenting. During our lifetime, the environment and mere chance become flesh in the genetic sequence of each of our cells. Cancer is a good example to illustrate the complex internal harmonies of the “born or done” issue that focuses our debate. But it’s just an example. Brain development and mental illness is a topic closely related to this topic, although it may not seem so. Fred Gage of the Salk Institute of California has shown in recent years that our brain is a mosaic of neuronal clones with distinct genomes. As in the development of cancer, different areas of our brain have accumulated mutations during cell proliferation from fetal development to adulthood. There are several types of mutations – the favourite of theorists is the change of a single letter in the genome, but the one that draws the most attention in our brain is of a very different nature. Half of the human genome is what is called transposons, or moving elements, DNA segments containing some information, copies of itself that are inserted elsewhere in the genome. Almost all of these transposons are mere genomic fossils, but Gage has discovered one, the LINE 1 that remains active in the genome. It jumps from one place to another as we develop in the uterus and live outside of it, and especially in the cells destined to form our brain. When LINE 1 changes position in a brain stem cell, all of its descendants inherit the new position, although some of them add another jump to the previous one, and so on. A transposon like LINE 1 is a DNA text that means “grow and multiply.” The discoverer of these essential lines of code in evolution was the twentieth century’s most brilliant geneticist, Barbara McClintock, who took 40 years to give her the Nobel Prize for some reason that no one has […]

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