Sniffing Out The Evolution Of Rodent Pheromones

According to researchers in Japan, rodent pheromones may have originated from a combination of two ancient vertebrate genes.

AsianScientist (Nov. 30, 2020) – Experts from Japan have traced the evolutionary origins of genes that allow mice, rats and other rodents to communicate through smell. Their results were published in Molecular Biology and Evolution.

In popular culture, pheromones are commonly thought of as airborne aphrodisiacs—with one whiff sparking a mating frenzy. While the search for human pheromones has so far proven elusive, they certainly exist in other members of the animal kingdom. After all, pheromones are essentially chemical cues that animals release to trigger specific behaviors.

Male mice, for instance, release a pheromone known as the exocrine-gland secreting peptide 1 (ESP1) in their saliva and tears. ESP1 makes female mice more receptive to mounting mates. Meanwhile, in males, it enhances aggressiveness upon encountering urine from other, unfamiliar males encroaching upon their territory.

Seeking to uncover the origins of ESP1, Associate Professor Yoshihito Niimura from the University of Tokyo and his team scoured the genomes of 100 different mammals in hopes of finding similar genes from the ESP family. They found ESP genes only in two closely-related rodent lineages: the Cricetidae family of hamsters and voles and the Muridae family of mice, rats and gerbils.

Interestingly, the researchers discovered that the Muridae family had a second group of additional ESP genes.

“We can imagine about 35 million years ago, the common ancestor of Muridae and Cricetidae formed the first ESP genes. Eventually, approximately 30 million years ago, the ancestor of Muridae duplicated and expanded these ESP genes. So now mice have many more ESP genes than the Cricetidae rodents,” said Niimura.

The team also found that ESP proteins and α-globin—which forms part of our blood hemoglobin—share a distinctive spiral shape. DNA sequencing revealed that splicing multiple α-globin genes together resembled parts of the ESP gene, suggesting that the latter may have originated from the former.

Aside from α-globin, Niimura and his colleagues also identified similarities between the ESP gene and CRISP2, a gene expressed in mammalian reproductive tracts and salivary glands. As ESP proteins are released in mice saliva and tears, this finding suggests that the ESP gene may have also originated from CRISP2.

Given that hemoglobin and CRISP genes are both ancient genes found in the shared evolutionary ancestor of all vertebrates, genetic reshuffling of the two may have ultimately given rise to what would become the ESP gene in rodents. Moving forward, Niimura and his team intend to search for novel pheromones armed with their new knowledge of ESP’s evolution.

“The creation of new genes is not done from scratch. Nature utilizes pre-existing material. Evolution is like a tinkerer, using old things and broken parts to create [a] new device with a useful function,” said Niimura.

The article can be found at: Niimura et al. (2020) Origin and Evolution of the Gene Family of Proteinaceous Pheromones, the Exocrine Gland-secreting Peptides, in Rodents.


Source: University of Tokyo; Photo: Vivek Doshi/Unsplash.
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