Mucus Is So Convenient We’re Evolving It Over And Over Again, Study Says: ScienceAlert

The animal kingdom is practically dripping with mucus.

Amphibians, snails and slugs are some of the most famous masters of mucus, but even the most lonely microorganism can ooze slime from time to time.

In our own species, mucus is produced in the mouth, nose, throat, lungs, intestine, cervix and urinary tract, all for various purposes.

Yet the origin of the world’s slime is a mystery.

Despite the many similarities between mucus, many forms have evolved in parallel and not in a branching, tree-like fashion.

Across glands and between mammals, a small study found that many mucus genes don’t actually share a common ancestor.

This is unusual because most genes with similar functions come from a shared ancestral gene that is passed down from generation to generation as it confers survival benefits.

Even in our own species, the genes that code for mucus proteins belong to several families. One secretes gel-forming mucus proteins, while another produces mucus proteins bound to the membrane of a cell. There are also “orphan” genes that code for mucus production that don’t quite match elsewhere.

Each of these distinct lineages probably evolved independentlyand researchers now think they’ve figured out where they came from.

By comparing genes coding for mucus, known as mucin genes, across 49 mammalian species, the team found that non-mucin proteins can evolve into slimy mucin proteins when repeated short chains of amino acids (building blocks of proteins) are added again.

Among all the mucin genes studied, these random repeats were counted 15 different times.

In other words, some genes in mammals that code for non-mucin proteins tend to stickiness over time. These proteins rich in organic acid proline are the most likely to go slimy with generations, according to the authors of the current study.

“I don’t think it’s been known before that protein function can evolve in this way, from a protein gaining repeat sequences,” said evolutionary biologist Omer Gokcumen of the University at Buffalo.

“A protein that isn’t mucin becomes mucin simply by gaining repeats. It’s an important way that evolution creates mud. It’s an evolutionary trick, and we’re now documenting that it happens. again and again.”

The authors came across their discovery by chance while studying human saliva. During the experiments, they noticed that a particular mucin gene in humans showed similarities to another seen in mice.

When they tried to find common ancestry, however, they failed.

The mucin gene in mice appears to have evolved independently, although part of the gene shares a structure seen in genes responsible for human tears, which are not considered mucus.

“We think that somehow this tear gene ends up being repurposed,” Explain Gokcum

“It gains repeats that confer mucin function, and is now abundantly expressed in mouse and rat saliva.”

If Gokcumen and his colleagues are correct, their results offer scientists a new mechanism of genetic evolution – the formation of new gene function without the usual process of a gene duplication event.

This parallel series of mutations in unrelated genes resulting in the same function is an example of convergent evolution (where selective pressure shapes the same function from unrelated biological origins, such as bat and bird wings) occurring at the genetic level.

“If these mucins keep evolving from non-mucins over and over again in different species at different times, that suggests there is some sort of adaptive pressure that makes it beneficial,” Explain Petar Pajic, evolutionary geneticist from the University at Buffalo.

“And then, on the other end of the spectrum, maybe if that mechanism goes off the rails – happens too much or in the wrong tissue – then maybe it can lead to diseases like certain cancers or mucosal diseases. “

While the study of mucus may not seem like the most magical of scientific endeavors, it’s hardly a pursuit to be sniffed at.

The study was published in Scientists progress.

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