2023-08-24 16:56:31
by Laura Cuppini
Work completes set of human chromosomes and adds 30 million new bases to genome map currently used as reference
The human Y chromosome and its role in the development of disease have long been a mystery. Now part of the puzzle has been unraveled by an international study led by the National Human Genome Research Institute (USA), published in the scientific journal Nature, showing for the first time the complete sequences of 43 Y chromosomes. An essential step forward in understanding the role of this chromosome in evolution and human biology. The 43 structures sequenced cover 180,000 years of human evolution.
Sex chromosomes
Chromosomes are structures made up of DNA and proteins, are found in the nucleus of cells and contain the individual’s genetic information. Each human cell contains 23 pairs of chromosomes. X and Y determine male or female sex (XY or XX pairs respectively): it has been hypothesized that they originated from a structurally similar pair of chromosomes and that Y subsequently underwent significant degradation, losing 97% of its set of genes over millions of years. Consequently, the possibility that human Y chromosomes may disappear completely in the distant future is being considered by scholars. for example, it has been observed that some males lose them in cell division during aging, with unclear consequences on health.
The two new studies
The Y chromosome contains numerous repetitive sequences that make complete sequencing difficult. But two works, including the one mentioned above, have made it possible to take important steps forward. The Telomere-to-Telomere (T2T) consortium has published the first complete sequence of the Y chromosome from a single individual of European ancestry in a study that was also published in Nature
(The complete sequence of a human Y chromosome). At the same time, a team led by Charles Lee, a professor at the Jackson Laboratory for Genomic Medicine in Farmington (USA), assembled the Y chromosomes of 43 unrelated males, nearly half of whom came from African ancestry. The two works, published simultaneously in the prestigious journal, reveal a highly variable nature of the Y chromosomes between individuals (from 45.2 million to 84.9 million base pairs, i.e. the unit of measurement of the length of sequences of double-stranded nuclei) and provide an important basis for future studies of male fertility and the development of certain diseases.
Genomic sequencing
The Telomere-to-Telomere consortium study presents the complete 62,460,029 base pair sequence of a Y chromosome, correcting several errors in the reference human genomic sequence (known as GRCh38) and adding to the current knowledge over 30 million pairs of bases (the human genome contains about 3.2 billion), in addition to 41 protein-coding genes present in the Y chromosome. Genomic sequencing technologies require the decomposition of DNA into short fragments (about 250 bases long). These fragments are then reassembled into the complete genome. The method is very accurate but does not work for the entire genome. Most of the sequences, including the current reference (GRCh38), are about 90% complete, because highly repetitive or complex sections are difficult to assemble accurately. GRCh38 is particularly deficient with regard to the Y chromosome. While the other sex chromosome X, larger and richer in genes, has been extensively studied, the Y chromosome (whose genes help govern crucial reproductive functions, including sperm production) has often been overlooked outside of studies of male fertility.
Men’s health
Now the work of the Jackson Laboratory, carried out in collaboration with other international research centers, has revealed for the first time a complete picture of the key characteristics of the Y chromosome. An important step, because the role of this chromosome in male health is poorly understood. Some indications of its importance have recently been brought into focus by two studies which investigated its functions in relation to the aggressive characteristics of colorectal and bladder tumors in men. One of the studies showed that tumors that have lost the Y chromosome can more effectively evade the immune shield of T cells (lymphocytes). The latest research shows that proper function of the Y chromosome gene is extremely important for men’s overall health, said Charles Lee.
August 24, 2023 (change August 24, 2023 | 16:56)
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