Genomic and proteomic analysis reveals that the regulatory role of chromatin is a eukaryotic innovation – Genetics News

In nearly all human cells, DNA that is two meters long must fit into a nucleus no more than 8 millionths of a metre wide. Like wool around a spool, the extreme space challenge requires DNA to wrap around structural proteins called histones. This coiled genetic structure, known as chromatin, protects DNA from damage and plays a key role in gene regulation.

Histones are found both in eukaryotes, organisms with specialized cellular machinery such as nuclei and microtubules, and in archaea, another branch of the tree of life consisting of prokaryotic unicellular microbes, that is, without a nucleus.

In eukaryotic cells, histones are modified by enzymes, constantly changing the genetic landscape for the regulation of gene expression and other genetic processes. Despite this primary role, the exact origin of chromatin is shrouded in mystery.

Researchers from the Center for Genomic Regulation (CRG) have now revealed that a natural storage solution first evolved in ancient microbes that lived on Earth between 1 and 2 billion years ago. The study was published today in the journal Ecology and Natural Evolution.

To go back in time, the researchers used information written into the genomes of modern organisms, organizing life forms according to the evolution of genes and chromatin-related proteins. They studied thirty different species obtained from water samples in Canada and France. Microbes were identified using modern genetic sequencing techniques that allow species identification by DNA filtering. They were then cultured in the laboratory for proteomic and genetic sequencing.

The researchers found that prokaryotes lacked the machinery to modify histones, suggesting that primitive chromatin at that time could have played an essential structural role but did not regulate the genome. In contrast, researchers have found ample evidence for proteins that read, write, and erase histone modifications in early divergent eukaryotic lineages such as malawimonad. Jevonella O’Keeffeancyromonas Fabomonas Madaror Discopan Nigeria GruberyMicrobes that have not yet been sampled.

“Our results confirm that chromatin’s structural and regulatory roles are as old as eukaryotes themselves. These functions are essential for eukaryotic life – since chromatin emerged, it has not been lost again in any life form,” says Dr. Xavier Grau-Bové, Postdoctoral Fellow In CRG and first author of the study. “We are now one step closer to understanding its origin, thanks to the power of measurement to reveal evolutionary events that occurred billions of years ago.”

Using the sequencing data, the researchers reconstructed the repertoire of genes possessed by the last common eukaryotic ancestor, the cell that gave rise to all eukaryotes. This organism had dozens of histone-modifying genes and lived between one and two billion years on Earth, with an estimated lifespan of 4.5 billion years. The study authors hypothesize that chromatin evolved in this microbe as a result of selective pressures in Earth’s primitive environment.

Dr. Arnau Sepe Pedro, a researcher at CRG and lead author of the study, points out, “Viruses and transmissible elements are genome parasites that regularly attack the DNA of single-celled organisms. This could have led to an evolutionary arms race to protect the genome, which led to the development of chromatin. As a defense mechanism in the cell led to the emergence of all eukaryotic organisms on Earth.Organization, as we observe in modern eukaryotes, especially multicellular organisms.”

According to the study authors, future research could focus on the evolution of histone-modifying enzymes in Asgardian archaea, microbes often described after a mythical region populated by Norse gods as an evolutionary stepping stone between archaea and eukaryotes. Researchers have found evidence that some types of Asgardian microbes such as LokiarcheotaIt has histones with eukaryote-like features and could be the result of convergent evolution.

The study is the result of a research project that began eight years ago. Led by the CRG researchers, the work builds on the collaboration of the CRG-UPF Proteomics Unit, the Institute of Developmental Biology (CSIC-UPF), Paris-Saclay University, the University of Montreal and the University of Vienna.

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