Helpless female elephants: epigenetics for beginners

0

During Mozambique’s 20-year civil war, due to intensive poaching, African elephant populations in Gorongosa National Park declined by 90%. As the population recovered after the war, a relatively large proportion of females were born helpless. The absence of tusk was not observed in male elephants from the same region. Now scientists have identified the genes responsible for female elephants born without tusks. At present, it has proven difficult to determine exactly what is going on genetically in these populations. This brings us to genetics and Charles Darwin.

In About the origin of species (1859), Darwin advanced his theory of natural selection and the survival of the fittest. He wrote that the characteristics developed by environmental influences will not be passed on to future generations; only traits transmitted by genes will be inherited, and genes take millennia to change.

A 1988 article published by John Cairns in Nature initiated a tectonic shift in genetics. The article described an experiment in which a particular strain of bacteria, E. Coli, which could not metabolize lactose (a sugar found in dairy products), was placed on a lactose medium (scientific jargon for foods on which bacteria thrive, usually in a Holy Bread). Instead of starving, the bacteria very quickly underwent genetic changes, which allowed them to digest lactose and thus survive. Cairns reported that at least in some cases, selective pressures could specifically drive mutations.

Goodbye, Darwinist orthodoxy. Cairns, some critics have said, “brazenly” raised the specter of possible Lamarckian hereditary mechanisms – one could not be more heretical than that in 1988. In the same issue of NatureFranklin Stahl, professor emeritus of biology at the University of Oregon, endorsed Cairns’ findings and presented his own model of how “site-directed mutations” can take place.

A decade after the Cairns article was published, Indiana University biology professor PL Foster wrote: “Much subsequent research has shown that mutation rates can vary and increase. during certain stresses such as nutritional deprivation. The phenomenon came to be called “adaptive mutation”. Today, the adaptive mutation has turned into epigenetics. And suddenly, all the university labs are studying it.

While Darwin’s work defines evolution as a process of accidental and random mutation between generations and the survival of the fittest, the new science of epigenetics is much closer to the much maligned theory of French biologist Jean-Baptiste. Lamarck, who suggested that an organism can switch to its characteristics of offspring acquired during its lifetime.

Epigenetics is the study of changes in the activity of genes which do not alter the genes themselves but which are still transmitted to at least one successive generation. These gene expression patterns are governed by the cellular material – the epigenome – which sits above the genome, just outside (hence the prefix ear-, which means above). A key part of epigenetics is methylation, in which a chemical group (methyl) attaches itself to parts of DNA, a process that acts as a dimmer on the function of genes in response to physical and psychosocial factors. Epigenetic “switches” turn genes on or off, and all points in between.

Methylation is a dynamic process, and methylation levels can change at any time and throughout a person’s life depending on the person’s experiences, whether external or internal. The process opposite to methylation is acetylation. Methylation decreases or completely silences the function of a gene while acetylation partially or fully activates the gene.

One of the main goals of epigenetics is to study the transfer of data from one generation to another by biological rather than psychological means. Biological inheritance evokes the idea that germ cells (sperm and eggs) are affected by important environmental events, and that these changes in the genome are then passed on to offspring. I suggest that it is this phenomenon that has led to the birth of helpless elephants in response to the threat of annihilation.

The field of epigenetics gained momentum when scientists several decades ago studied children born to pregnant women during a time of famine near the end of World War II in Holland. They discovered that these children carried a particular chemical mark, or epigenetic signature, on one of their genes. The researchers linked this finding to differences in the health of children later in life. The children became smaller than the Dutch average and had an above average body mass. Their children were also smaller and more susceptible to diabetes, obesity and cardiovascular disease. These changes were detectable over three generations.

Around the same time that Cairns was performing his experiments, Lars Olov Bygren of Umea University in Sweden wondered, “Could parents’ early life experiences change in any way? on the other hand, the traits they passed on to their offspring? Bygren and many other scientists have now accumulated a great deal of historical evidence to suggest that powerful environmental conditions (almost death by starvation, for example) can leave an imprint on the genetic material of eggs and sperm. These genetic fingerprints can bypass evolution and pass on new traits in a single generation.

But it is not only stressful or traumatic incidents that can alter gene expression (activity). David Clayton, a neurobiologist at the University of Illinois, found that if a male zebra finch heard another male zebra finch singing nearby, a particular gene in the bird’s forebrain would be stimulated and it would do so differently depending on whether the other finch was strange or not. and threatening, or familiar and secure. Songbirds demonstrated massive and widespread changes in gene expression in just 15 minutes.

We are learning that brain responses to social stimuli can be massive, involving hundreds, sometimes thousands, of genes. Just 20 years ago, no self-respecting geneticist or neuroscientist would have thought in their wildest dreams that social experiences lead to changes in gene expression and brain behavior.

Complex diseases such as cancer, diabetes, obesity, autism and birth defects are increasing in prevalence at rates that cannot be explained by classical genetics alone. Studies in humans and animals strongly suggest that epigenetic mechanisms may be responsible.

Compelling scientific evidence shows that our social lives, our interactions with others, and ourselves can alter our gene expression with a speed, scale and depth never before seen. Genes don’t make us who we are. Gene expression does. And gene expression varies depending on the life we ​​live. In other words, the food we eat, the water we drink, the air we breathe, our interpersonal relationships and our relationship to ourselves all affect us on a deep biological level which in turn affects our spirit.

Are genes important? Absoutely. But so is the physical, psychological and social environment, not only from birth but extending up to the nine months of the life of the womb, conception and, in many ways, several generations. further away. The advance of epigenetics shattered the old Darwinian paradigm of genetics.

More on this in The embodied spirit (2021).


Source link

Share.

Leave A Reply