In the photo: Researcher with a Neanderthal skull
As you know, geneticists consider up to 95% of all human DNA to be garbage, that is, not carrying any useful information. For a long time, scientists failed to shed light on why nature created such a large ballast. It has only recently become clear that researchers are rushing to discard junk DNA.
"Black box" from the past
Let's think of our DNA as a time-greasy, big and plump magazine. Nature has been leading it since time immemorial, on the pages there is a huge number of notes, edits. Each animal in the chain of evolution was marked by nature on these pages, then again, again and again, and so on until that epoch-making moment when, finally, a man appeared who was able to say: " Cogito, ergo sum " ("I think, therefore I exist"). There are many drawings, comments and even cartoons left on the pages of the "magazine" by the author: dinosaurs are drawn, sketches of webbed wings, furry paws, long mustaches, sharp ears and fluffy tails …: "There are no others, but those are far away."
This is what our junk DNA is, figuratively speaking. It contains fragments of genes and whole genes, some obscure additions to something that has not existed for a long time. Nature, as it were, tells us that we are descendants of creatures that have long disappeared in the abyss of time.
A significant part of human DNA, which contains working genes, occupies only 4-5%, that is, a microscopic volume of the total number of "journal entries". This leads to the fact that a very tiny change in the working DNA is enough to mutate or damage any of the genes. It often happens that hereditary diseases arise due to the fact that the entry in a significant part of the DNA is made with an error. In this case, if you remember our comparison with the magazine, even an incorrect comma may be enough.
For example, due to a mutation in DNA, the “glass man” syndrome occurs, in which collagen is synthesized incorrectly and the bones of a child are so fragile that they break from the slightest impact. But in nature, there are also positive, evolutionarily happy variants of gene breakdown. With such mutations, proteins in genes can assemble along a chain in a fundamentally new way, which can endow the body with new functions, and often implies the loss of atavistic, that is, old features. One of the most striking examples of this is the emergence of speech in humans, which was caused by mutations with the FOXP2 gene about 200 thousand years ago.
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Get rid of the rubbish from theory
Junk DNA is present not only in humans, but also in animals, absent only in the simplest viruses. After conducting a series of studies, it turned out that some parts of junk DNA are strikingly similar in many species of living things that stand far from each other in the process of evolution. In particular, scientist David Kingsley and a group of colleagues from Stanford, after their experiments, stated that there are more than 500 pieces of DNA that are identical in the studied animals, but absent in humans. This study also compared human DNA with the DNA of our "close relative" - chimpanzees, with which the genes match is 96 percent. The result was unexpected - the differences between humans and chimpanzees and many other mammals for the most part are not in genetic acquisitions, that is, not in the presence of any new genes that have appeared in him,and in genetic losses - the absence of some fragments in the DNA chains. Surprisingly, it is true: we lack these missing fragments in non-coding, that is, junk DNA. Accordingly, the conclusion suggests itself that it is not so trash …
Let's give an example: the missing part in human DNA falls on one of the fragments of the genome associated with the production of the androgen receptor AR, which responds to male hormones - testosterone and dihydrotestosterone. There is an assumption that the loss of this particular fragment led to the disappearance in humans of features characteristic of chimpanzees and other mammals, namely: hard sensitive vibrissae hairs (for example, whiskers in cats), as well as keratin spines on the penis. Many mammals have these distinctive features, from mice to monkeys.
The second piece of DNA that has disappeared from humans is located near the GADD45G gene. This gene is in charge of cell growth, and its absence leads to harmful consequences for the body - uncontrolled cell growth, leading to the appearance and growth of cancerous tumors. However, the absence of DNA fragments next to this gene contributed to the increase in the size of some areas of the human brain. In embryos of mice and chimpanzees, which were artificially deprived of such a fragment, the visual zones of the brain and a number of other brain regions began to increase.
So junk DNA is, perhaps, completely undeservedly considered a collection of old and meaningless "records" inherited from our distant ancestors. Not playing a direct role in the transfer of genetic information, it behaves like a "gray cardinal", that is, controls the surrounding genes, and also "substitutes itself under the blows of fate", taking on the attacks of viruses and mutations.
John Mattick's discovery
Looking for a black cat in a dark room, especially if the darkness is up to 95 percent of its volume, is a thankless task. But circumstances can change dramatically if you suddenly manage to illuminate a dark room, even with a very dim light.
Australian scientist John Mattick was able to shed some light into the darkroom of junk DNA. The light is not yet too bright, shadows are visible on the walls, objects in the twilight take distorted forms, but his merit is obvious: he was able to achieve an official revision of the scientists' idea of junk DNA as a collection of ballast that we inherited from ancient times. And for this, the first Australian scientist to be awarded the Chen Award for Excellence in Genetic and Genomic Research.
“The ideas I came up with 10 years ago were pretty radical, but I always thought I was right,” said Mattik, who recently became Garvan's new CEO. He explains: “When James Watson and Francis Crick discovered that DNA was made up of a double helix about 50 years ago, scientists began to believe that most genes are written instructions for proteins, the building blocks of all body processes. This assumption was true for bacteria, but not as complex organisms as humans."
The scientist found that parts of junk DNA, among other things, are responsible for the production of RNA - ribonucleic acid. And the RNA itself, previously considered completely non-coding, that is, non-working, is a whole network that controls the work of the body.
"An obvious and very exciting possibility is that there is another layer of information expressed by the genome - noncoding RNA forms a massive and previously unrecognized regulatory network that drives human development," concluded Mattik.
RNA is a rather curious thing. Like DNA, it can store information about biological processes. RNA can also be used as the genome of viruses and virus-like particles. For example, the influenza virus at all stages contains a genome consisting exclusively of RNA. In addition, RNA is considered to be a kind of “ancestor” of DNA, which has long since transferred all control functions to its young and more successful “heir”. And now it turned out that RNA has not yet lost all the reins of control over our body! In particular, many scientists now assume that RNA is necessary for humans for brain plasticity and learning. It is assumed that further research on RNA will help in understanding the mechanisms of development of some diseases.
In short, genetics is getting closer to revising some of its foundations, and there are fewer and fewer dark spots in the theory of junk DNA.
