HomeScience and ResearchScientific ResearchSecrets Of Chromatin That Gave Life To All Eukaryotic On Earth Revealed

Secrets Of Chromatin That Gave Life To All Eukaryotic On Earth Revealed

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Almost in every human cell, the nucleus is only 8 millionths of a meter wide, and the DNA is two meters long. The tremendous space challenge requires DNA to wrap around structural proteins called histones, much like wool around a spool. Chromatin is a coiled genetic architecture that protects DNA from harm and regulates gene expression.

Histones can be found in both eukaryotes, which are living organisms with specialized cellular machinery like nuclei and microtubules, and archaea, which are single-celled bacteria that are prokaryotic, meaning they lack a nucleus.

Enzymes modify histones in eukaryotic cells, constantly altering the genomic landscape to regulate gene expression and other genomic functions. Despite its critical role, the exact genesis of chromatin has remained a mystery.

Researchers at the Centre for Genomic Regulation (CRG) have discovered that nature’s storage solution first arose between one and two billion years ago in ancient bacteria living on Earth. The findings were just published in the journal Nature Ecology and Evolution.

To travel back in time, the researchers exploited information written in modern organisms’ genomes, grouping living forms based on the evolution of genes and proteins connected to chromatin. They looked at thirty distinct species found in Canadian and French water samples. Modern gene-sequencing tools, which allow the identification of species by filtering DNA, were used to identify the bacteria. They were cultivated in the lab after that for proteome and genomic sequencing.

The researchers discovered that prokaryotes lack the machinery needed to change histones, implying that archaeal chromatin may have had a structural purpose but did not regulate the genome at the time.

For the first time, researchers have identified evidence of proteins that can read, write, and erase histone modifications in early-diverging eukaryotic lineages, such as the ancyromonad Fabomonas tropica, the discoban Naegleria gruberi or the malawimonad Gefionella okellyi.

“Our results underscore that the structural and regulatory roles of chromatin are as old as eukaryotes themselves. These functions are essential for eukaryotic life — since chromatin first appeared, it’s never been lost again in any life form,” said Xavier Grau-Bové, the study’s first author. “We are now a bit closer to understanding its origin, thanks to the power of comparative analyses to uncover evolutionary events that occurred billions of years ago.”

The researchers used the sequence data to rebuild the gene repertoire of the Last Eukaryotic Common Ancestor, the cell that gave rise to all eukaryotes. This living organism possessed dozens of histone-modifying genes and lived on Earth between one and two billion years ago, when it was thought to be between one and two billion years old. According to the researchers, chromatin formed in this microbe as a result of selective forces in Earth’s primordial environment.

“Viruses and transposable elements are genome parasites that regularly attack DNA of single-celled organisms,” adds Dr. Arnau Sebe-Pedrós, senior author of the study.

“This could have led to an evolutionary arms-race to protect the genome, resulting in the development of chromatin as a defensive mechanism in the cell that gave rise to all known eukaryotic life on Earth. Later on, these mechanisms were co-opted into elaborate gene regulation, as we observe in modern eukaryotes, particularly multicellular organisms.”

The authors of the paper suggest that future research might examine the evolution of histone-modifying enzymes in Asgardian archea, which has been referred to as an evolutionary bridge between archaeotes and eukaryotes due to their mythological origins.

Some Asgardian microorganisms, such as Lokiarchaeota, have histones with eukaryotic-like characteristics, which could be the product of convergent evolution, according to the researchers.

Image Credit: Getty

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