$817,000
New York
National Institutes of Health
Drool from monkeys, gorillas, orangutans, macaques, and
humans was compared in an attempt to gain “insights into evolution of saliva.”
The study was funded, in part, from two National
Institutes of Health (NIH) grants totaling $817,000 to the State University of
New York at Buffalo (UB).
DNA samples of saliva from the primates were purchased
and then analyzed using polymerase chain reaction (PCR). PCR is a technique that copies and amplifies small
segments of DNA to conduct molecular and genetic analyses.
The research specifically focused on the salivary mucin-7
(MUC7) gene, that “tells the body how to create a salivary protein of the same
name.” This protein, “which is long and
thin, forms the backbone of a bottlebrush shaped molecule that helps to give
spit its slimy, sticky consistency.”
The analysis found the instructions within the MUC7 gene
“for building important components of the bottlebrush were repeated multiple times”
in each of the five primate species studied. Gorillas had the fewest copies of this
information (4-5), while African green monkeys had the most (11-12). Humans
fell somewhere in between, with 5-6.”
The researchers then simulated evolutionary changes in
the composition of the saliva gene over 11 million years from a common
ancestor. They assumed “every 1 million
year [sic], there is a random gain or loss of 0.5/1.0/1.5/2.0 copies for
Orangutan and the common ancestor of Human, Chimpanzee and Gorilla separately.
At 8 million years ago, the common ancestor of Human and Chimpanzee separated
from Gorilla and they started the copy number gain and loss simulation
separately. The same simulation continues to 5 million years ago that Human and
Chimpanzee separated from each other, and start their copy number gain/loss
process independently until present. We simulated this process 1,000 times for
4 different copy-number-change rates (0.5/1.0/1.5/2.0 copies per million year),
and for each simulation, calculated the variation of final state of simulated
copy numbers for Human, Chimpanzee, Gorilla and Orangutan. The observed copy
number state in present is Human 5 or 6 copies, Chimpanzee 5 copies, Gorilla 4
or 5 copies, and Orangutan 6 or 7 copies.”
So what does that all mean?
“This diversity in humans and other primates is ‘fodder
for rapid evolution,’” the scientists write in a study published in Scientific
Reports. It is “unusual for members of a
single species to have varying numbers of tandem repeats,” which are “short
strings of DNA found multiple times inside the gene.”
The researchers speculate that by “having numerous copies
of the repeated instructions likely conferred an evolutionary advantage to
primates— possibly by enhancing important traits of saliva such as its
lubricity.”
The authors of the study do caution that “gene
predictions, especially for genes that have repeat content as in MUC7, may be
error prone.”
As sticky as the subject may be, saliva does serve
important functions. Other studies— including some conducted at UB— have
examined the importance of saliva for human health. While the findings of those
efforts may lead to exciting scientific breakthroughs, this particular study is
nothing to drool over.
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