the amazing adventure of centromere evolution

Remember your college biology textbooks and those chromosome pictures with their X shape. Almost every X has a centromere in the center (it is very eccentric on our chromosomes 13, 14, 15, 21, and 22). These centromeres play a crucial role in the division of our cells: they ensure a balanced distribution of chromosomes in each daughter cell. A group of one hundred proteins, kinetochores, play an important role in this process. It stops at the centromere so that other gears can grab and then separate the chromosome pairs.

But the DNA of these centromeres remained “dark matter” until then. Genome reading methods made it difficult to decipher the text. Nevertheless, on 31 March, the American consortium Telomere-to-Telome (T2T) announced that Science so that it can finally be read thanks to a new DNA sequencing technique.

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This reading revealed the strange evolutionary process of centromeres. But first let’s see what their DNA is made of. It is basically a series of repetitions of the same “word”. This “word” is a sample of 171 DNA “chemical letters” with variations. This is repeated tens of thousands of times (in tandem, two strictly identical patterns follow each other).

The core of the centromere is in the middle of the famous kinetochore. “But during evolution, this active zone is constantly being renewed because new mutations are taking place in it.”, explains Loran Dure, a specialist in evolutionary biology at the University of Lyon. These new mutations occur in one of the 171-letter patterns, creating a new version of this article. “It is possible that there is selection pressure in the center of the centromere because it is its active heart: ‘the best options’ [les plus efficaces pour répartir les chromosomes de façon équilibrée] will be passed on to offspring.accepts Loran Dure.

This new version will drive out older models at the edges of the centromere. “Older sequences have a higher number of random mutations indicating that they are no longer used by the cellin a press release explains the University of Berkeley, which participated in the studies published Science. The latest sequences in which the kinetochore is attached are much less variable. »

Fossil layers

“By deviating from the active site of the centromere, DNA sequences are increasingly degraded, adds Nicolas Altemose, a postdoctoral researcher at the University of Berkeley, co – author of four of the six published articles. Science. On the other shores of this repetitive sea, we begin to see the ancient centromere, which was probably linked to the kinetochore by our distant primate ancestors. Those are as layers of fossils. »

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Georgie Collins

"Falls down a lot. Writer. Passionate alcohol maven. Future teen idol. Hardcore music practitioner. Food fanatic. Devoted travel fan."

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