The animal kingdom is practically dripping in mucus.
Amphibians, snails, ducks snails It is among the more famous masters of mucus, but even the loneliest microorganism can ooze a sticky slime from time to time.
In our own species, mucus is produced in the mouth, nose, throat, lungs, intestines, cervix and urinary tract, all for various purposes.
Yet the origin of slime on Earth is a mystery.
Despite the many similarities between mucus, many forms have evolved in parallel rather than in a branching, tree-like manner.
A small study between glands and among mammals revealed that many mucus genes do not actually have a common ancestor.
This is unusual because many of the genes with similar functions originate from a common ancestral gene that is passed down through generations because it benefits survival.
Even in our own species, the genes encoding mucus proteins belong to several families. One secretes mucus proteins that form gels, while the other produces mucus proteins attached to the cell membrane. There are also ‘orphan’ genes that encode mucus production that doesn’t quite fit anywhere else.
Each of these separate lineages probably developed independentlyand researchers now think they’ve figured out where they came from.
When comparing mucus-encoding genes, known as mucin genes, in 49 mammalian species, the team found that non-mucin proteins can turn into slimy, mucinous proteins when repeated short chains of amino acids (protein building blocks) are re-added.
Among all mucin genes studied, such random repeats were counted 15 different times.
In other words, some genes encoding non-mucin proteins in mammals tend to lean towards slimy over time. Proteins rich in organic acids proline According to the authors of the current study, it is more likely to go over the generations emotionally.
“I don’t think it was known before that protein function could evolve in this way from a protein that gains repeated sequences” says Omer Gokcumen, an evolutionary biologist at the University of Buffalo.
“A protein that isn’t mucin becomes mucin by simply regaining it. This is an important way evolution has made it slimy. It’s an evolutionary trick, and we’re now documenting that it happens over and over.”
The authors made their discovery by accident while working on human saliva. During the experiments, they noticed that one particular mucin gene in humans had similarities with another seen in mice.
But when they tried to find a common ancestor, they were unsuccessful.
The mucin gene in mice appeared to have evolved independently, but part of the gene shared a pattern seen in the genes responsible for human tears, which are not considered mucus.
“We think that somehow this tear gene has been redesigned” explains Gokcumen.
“It acquires repeats that give it a mucin function and is now abundantly expressed in mouse and rat saliva.”
If Gökcümen and his colleagues are right, their results provide scientists with a new mechanism of genetic evolution – the formation of a new gene function without the usual process of gene duplication.
An example is this series of parallel mutations that result in the same function in unrelated genes. convergent evolution It happens at the genetic level (where selective pressure molds the same function from unrelated biological origins like bat and bird wings).
“If these mucins continue to evolve repeatedly from different types of mucins at different times, it indicates a kind of adaptive pressure that makes it useful.” explains Evolutionary geneticist Petar Pajic of the University of Buffalo.
“And then, at the other end of the spectrum, maybe if this mechanism ‘derails’ – if it’s getting too much or in the wrong tissue – then maybe it could lead to diseases like some cancers or diseases of the mucous membranes.”
While working on mucus may not sound like the most magical scientific endeavor, it’s not much of a smack to smell.
Study published Science Advances.
