Humans can someday evolve to spit venom like snakes, finds study

Oral venom systems have been evolutionary in the vertebrates, and therefore the human salivary glands were found to contain venom gland gene expression preserved for over several thousands years. Both mice and humans share ancient functional cores and have the potential to become venomous like reptiles, a new study, that analyzed the ancient, conserved gene regulatory network and rise of oral venom systems, found. The results were published on March 29 in the journal PNAS. 

“Venoms are proteinaceous mixtures that can be traced and quantified to distinct genomic loci, providing a level of genetic tractability that is rare in other traits,” scientists said, "studies of venom in snakes have allowed comparisons of the relative importance of sequence evolution vs. gene expression evolution,” they continued, adding that the present-day human toxins can modify venom due to the genes that interact with each other. According to the study, scientists attempted to find the source of snake poison and discovered that it was formed due to the complex oral venom systems that likely originated from a gene regulatory network conserved across species known as the “metavenom network.” 

[Expression pattern of orthologs between venom gland in snakes and salivary gland in mammals was surprisingly well conserved. Image Credit: PNAS journal]

[Gene families in the metavenom network have not only evolved more rapidly in the lineage leading to snakes but have also undergone more expansions in snakes. Credit: Journal PNAS]

Evolutionary mechanisms transformed glands

The study purported that “comparative transcriptomics found that the venom network is conserved between venom glands of snakes and salivary glands of mammals.” As per the scientists, the tissues have transformed with time to perform different functions due to the evolutionary mechanisms, and hence, human salivary glands have their links to the snake’s venom glands. "It definitely gives a whole new meaning to a toxic person,” the lead researcher of the study  Agneesh Barua said.  A team of scientists from the Okinawa Institute of Science and Technology Graduate University and the Australian National University-led analysis of the venom genes in reptiles. They used a Taiwan habu snake - a pit viper found in Asia and extracted at least 3000 venom genes from the metavenom network. 

 "Many scientists have intuitively believed this is true, but this is the first real solid evidence for the theory that venom glands evolved from early salivary glands. While snakes then went crazy, incorporating many different toxins into their venom and increasing the number of genes involved in producing venom, mammals like shrews produce simpler venom that has a high similarity to saliva," Study author Agneesh Barua said. 

“Oral venom systems started with a common gene regulatory foundation, and underwent lineage-specific changes to give rise to diverse venom systems in snakes, lizards, and even mammals,” scientists found. And mammals’ saliva shared ancestry with the snake’s venom system. Metavenom network gene expression patterns were found in the tissue groups of nine species: human, chimpanzee, mouse, dog, anole, habu, cobra, chicken, and frog, according to the study.