When the worms migrated from salt water to fresh water, they experienced a massive rearrangement of their genetic material.
The event ripped out once-functioning genes, including those involved in key cell division processes, making it a natural choice for earthworms, leeches and other Convex part It is known as the relative with the most confusing genome.
“Everything was broken and rearranged in a completely random way,” said Rosa Fernández of the Spanish National Institute of Evolutionary Biology (CSIC-UPF). Said Christie Wilcox science“I had my team repeat the analysis a thousand times.”
Three groups of researchers independently reached the same conclusion, overturning a long-held assumption that animal species need a certain level of genetic stability to avoid extinction.
Evolutionary biologist Carlos Vargas-Chavez and colleagues at CSIC-UPF found that gene loss was about 25 percent higher in the lineage of worms that evolved into Clitellata than in other relatives.
They think the worms’ genomes may have shuffled in response to the change to a new habitat, but they haven’t yet determined whether the worms branched out from fresh water to land first, or whether their genes ventured to new locations on their genetic molecules (chromosomes) first.
“While the timing of this genetic rearrangement remains unclear, we argue that it is highly unlikely that the genetic features observed in the clitellates arose through rearrangement over time,” the researchers wrote. Explain in the paper.
Instead, the patterns observed by Vargas-Chávez and team suggest a “single-cell catastrophe” that essentially shatters the worm’s genome over a short period of time. They suggest that a sudden change in environmental conditions, including a sudden exposure to more oxygen or radiation, could trigger this.
The authors compare the worm’s remarkable genome changes to processes identified in: cancer cell.
Maximum bilaterally symmetrical animalAnimals like us, with mirror images on both sides, were thought to have highly conserved parts of their chromosomes. This stability is essential for properly aligning the two strands of DNA that form when they separate during reproduction and pair with one strand from each parent.
From sponges to monkeys, genomes contain long ribbons of genes that are held together in a specific order among distantly related species. preserved for hundreds of millions of years.
These ribbons can move to some extent, but the order within this section remains relatively constant. This is not the case with leeches and earthworms.
“Overall, the ancient bilaterian genome structure is completely lost within the uplifted animals,” said a second team led by Thomas Lewin, an evolutionary genomicist at the Taiwan Biodiversity Research Center. Establish.
The Ruin team is investigating how these unexpectedly drastic changes in chromosomes influenced animal evolution.
“Examples of genome-wide conservation are extremely rare,” Lewin and colleagues write. Explained in another studyContrary to previous assumptions, this is argued to be “the exception, not the rule.”
But while large-scale genetic reconfiguration may be more common than previously thought, it comes with risks, as expected. Third Team 2,291 genomes were examined If drastic chromosomal changes are found in any major animal clade, they could be associated with a major extinction event.
“The important question is how this profound genomic reorganization event did not lead to extinction.” write Vargas-Chavez and his colleagues.
The researchers found that the ancestral marine worm’s genome appeared to be disorganized and “much looser” than that of other animals.
“This may have resulted in a high resilience to deep genome remodeling that occurs after chromosome scrambling,” the team said. ConcludeIt also suggests that these dramatic genetic rearrangements are likely to continue in this species.
This study is available on a preprint server. BioArchiveWith two relevant documentAnother one has been published Molecular Biology and Evolution.
