A mesmerizing journey of evolution
The researchers found that mice lacked MUC7, a tiny salivary mucin seen in humans. However, MUC10, a salivary mucin of comparable size, was present in the rodents. So the researchers wondered if these two proteins were related from an evolutionary perspective.
Even though the answer to this was no, the research revealed that while MUC10 did not appear to be connected to MUC7, PROL1, a protein identified in human tears, did have some structural similarities to MUC10. Without the sugar-coated bottlebrush repetitions that define MUC10 as a mucin, PROL1 resembled MUC10 in appearance.
“We think that somehow that tear gene ends up repurposed,” states Gokcumen. “It gains the repeats that give it the mucin function, and it’s now abundantly expressed in mouse and rat saliva.”
The researchers also wondered if other mucins could have formed the same way and decided to look into it. They came across numerous instances of the same phenomenon. The scientists identified 15 instances in which evolution appears to have transformed non-mucin proteins into mucins by adding PTS repeats, even though many mucins had a common ancestor among different groups of mammals.
“How new gene functions evolve is still a question we are asking today,” says Pajic, a UB Ph.D. student in biological sciences. “Thus, we are adding to this discourse by providing evidence of a new mechanism, where gaining repeated sequences within a gene births a novel function.”
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“I think this could have even broader implications, both in understanding adaptive evolution and in possibly explaining certain disease-causing variants,” Pajic adds.