The international T2T consortium announced the successful completion of the work. Twenty years after sequencing the human genome, scientists have figured out the remaining portions – about eight percent – that were the most difficult to sequence. This is reported in a press release from the U.S. National Institutes of Health (NIH); an article about the work was published in the journal Science.

The human genome was almost completely defined back in 2003, as part of a global study of the Human Genome Project. For that time, the task was enormous, and hundreds of researchers from different universities and countries participated in its solution. They had successfully sequenced about 92 percent of DNA – the genes and sections between them that make up euchromatin. In cells, euchromatin is active, so it remains “unraveled” and twists into a more compact form only to divide.

In contrast, heterochromatin permanently maintains its compact form and does not encode proteins. It performs primarily auxiliary functions, maintaining the structure and integrity of chromosomes, ensuring their interaction with proteins, and the like. Heterochromatin is located, for example, in centromeres – the sites where a pair of sister chromosomes join together to form a recognizable “X” – and in telomeres, the end sites of chromosomes. This DNA is characterized by the presence of long repetitive sequences, the identification of which is a great challenge.

Recall that to sequence a strand of DNA, you have to cut it into many fragments, then determine the nucleotide sequence of each fragment and, finally, combine the resulting codes in the correct original order. But if the code is hundreds of short repeats that are indistinguishable from one another, such work becomes virtually impossible. That is why the Human Genome Project participants had to skip this small part of the genome, for the benefit of science and medicine it plays far from the main role.

However, a complete understanding of the structure of the genome requires at least a complete sequence, and over time, sequencing technologies have made great strides forward. Therefore, a new consortium Telomere to Telomere (T2T) began its work a few years ago with the goal of understanding heterochromatin regions. In 2021, its participants presented a “rough” result, and now – the final, covering the missing eight percent of the genome.

To do this, the biologists had to go for a little trickery, using DNA from a cell line with a hereditary disorder for sequencing, as a result of which they carry two identical copies of each chromosome (instead of one maternal and one paternal). Therefore, the T2T consortium has not completed its work: at least its members have yet to sequence the heterochromatin on the unpaired Y chromosome.

The importance of this work should not be underestimated. In the past, many sections of heterochromatin were indeed considered “junk” DNA, accumulated over billions of years of evolution and playing no role in the life of the human body. Today, scientists understand that these fragments have important functions, not only structural, but also, for example, regulatory, controlling the activity of euchromatin genes. Many severe diseases are associated with heterochromatin malfunction.

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Researchers from the University of Leicester and Leicester General Hospital (UK) examined data from 405,981 people stored at the British Biobank and confirmed that a faster walking pace, regardless of overall physical activity level, is associated with telomere length, the end sections of chromosomes considered a marker of biological age. The findings are published in the journal Communications Biology.

Walking is a simple and accessible form of exercise for people of all ages. Scientists have long claimed that walking is not only generally beneficial, but also reduces the risk of cardiovascular disease and all-cause mortality, and if one walks at a faster pace daily, one can even increase life expectancy. However, it has not been fully understood how walking speed is related to biological age, which reflects the degree of development and maturity of the body.

Telomeres are a complex of telomere DNA and associated proteins, they protect the ends of chromosomes from degradation, fusion and abnormal recombination of DNA strands. Telomeric regions gradually shorten with each cell division, contributing to replicative, or cellular aging (caused by the loss of the cell’s ability to divide). In addition, telomere shortening is regulated by factors such as oxidative stress and inflammation.

As suggested by previous studies, there is a link between high levels of physical activity and endurance and longer chromosome endings: therefore, physical activity via telomere lengthening helps to slow biological aging. But according to the Leicester scientists, most of the work on this topic that involved humans was small and did not fully address the causal relationship between simple types of exercise like walking and telomere length.

The average age of the British Biobank participants, whose genetic information formed the basis of the new study, was 56.5 years old, had a body mass index of 27.2, 54% were female and 95% were white. About half of the participants (212,303, 52.3%) reported walking “at a medium pace,” 6.6% (26,835) walked slowly, and 41.1% (166,843) walked at a fast pace. Compared with those who were not in a hurry, people in groups one and three were slightly younger, more likely to have never smoked and less likely to have taken cholesterol or blood pressure lowering medications, less likely to have chronic illnesses or to be restricted in movement. Those who were “slow” were more likely to be obese and prone to drinking alcohol.

“Those who walked at a medium or fast pace had significantly longer telomeres than those who walked slowly,” the researchers wrote. A secondary analysis, in which data from an accelerometer were taken into account, showed that if one did most of the daily physical activity at a higher intensity, the end sections of the chromosomes would be longer. The relationship persisted after other factors were taken into account.

“We found evidence that walking pace has a causal relationship with telomere length. Depending on the simulated difference in walking pace (from slow to medium pace or from medium to fast), there was an increase in the standard deviation of telomere length of 0.192 and 0.226 before and after accounting for body mass index, respectively,” the researchers add. They calculate that there is a 16-year difference in biological age between fast- and slow-moving individuals, although the adjusted analysis gives a difference of two years.

In the future, the researchers plan to confirm whether behavioral interventions aimed at increasing walking speed or increasing the intensity of physical activity can slow telomere degradation.

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Researchers at the University of Michigan conducted a study involving first-time interns. DNA analysis showed that their telomere shortening accelerated six times over the first year compared to normal progression. The work was published in the journal Biological Psychiatry.

Telomeres are the end sections of chromosomes, which are usually compared to protective caps because they keep the ends of chromosomes intact. However, because DNA polymerase is unable to synthesize a copy of the DNA from the very end, telomeres shorten with each division. Therefore, telomere length has been associated with a person’s lifespan and predisposition to disease. Last year, researchers at George Mason University showed that having children affects telomere length. Women who gave birth had shorter telomeres than women who did not have children. In addition, telomere shortening has been linked to cardiovascular disease and cognitive decline. Now researchers at the University of Michigan have decided to find out if there is a link between telomere length and stress.

For the experiment, they selected 250 interns who were entering their first year of practice at the hospital. The scientists took DNA samples before they started and after a year to compare how telomere length had changed. At the same time, they asked the volunteers to fill out a questionnaire that revealed the length of the work week and stress levels.

The authors observed that over the past 12 months, telomere length depletion in the interns accelerated six-fold compared to the average rhythm (from 6465.1 ± 876.8 base pairs to 6321.5 ± 630.6). Moreover, they highlighted a correlation between the number of work hours and the rate of acceleration. The standard work week includes 64 and a half hours, but some interns worked 80 hours a week. It was in them that telomere depletion progressed the fastest. The opposite trend was seen in those who chose the least busy schedule.

“Studies show that telomeres are indicators of aging and risk of various diseases, but this experiment suggests that their length also serves as a biomarker that reflects the effects of stress,” said one of the paper’s authors, psychiatrist Srijan Sen.

If this assumption is correct, the results obtained by the University of Michigan researchers could be extended to other stress-inducing professions.

Earlier, psychologists from the University of Michigan conducted a simple experiment that demonstrated that 20 minutes a day in nature is enough to significantly reduce cortisol levels.

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