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article imageStudy says toxic venom proteins 'born' from non-toxic genes

By Karen Graham     Dec 8, 2014 in Science
Arlington - Snakes and some lizard's venom are a cocktail of toxins, usually consisting of tens to hundreds of different proteins, and scientists have always defined an animal as venomous based on finding the toxic gene families in their oral cavities.
This way of categorizing snakes and lizards as being venomous is being challenged by researchers at The University of Texas at Arlington. They have also developed a new model explaining how snake venom evolved. The study, published in the journal Molecular Biology and Evolution, is based on a detailed analysis of groups of related genes, or what the researchers call "gene families" in tissues from different parts of the Burmese python, or Python molurus bivittatus.
The research team was led by assistant professor of biology Todd Castoe and including researchers from Colorado and the United Kingdom. They found similar levels of the so-called toxic gene families when they examined tissue specimens taken from the oral glands of the python, as well as tissue samples from the brain, liver, and other parts.
What the scientists learned is interesting, especially in categorizing animals as being venomous. By finding venom homologs at much lower levels in pythons, along with high variances in the different tissues, they found the genes are expressed in fewer organs compared with all other python genes. The team says the findings tell us much about the function of venom genes before they actually evolved into venoms.
“Research on venom is widespread because of its obvious importance to treating and understanding snakebite, as well as the potential of venoms to be used as drugs, but, up until now, everything was focused in the venom gland, where venom is produced before it is injected,” Castoe said. “There was no examination of what’s happening in other parts of the snake’s body. This is the first study to have used the genome to look at the rest of that picture.”
“The non-venomous python diverged from the snake evolutionary tree prior to this massive expansion and re-working of venom gene families. Therefore, the python represents a window into what a snake looked like before venom evolved,” Castoe said.
The scientists looked at 24 gene families shared by cobras, rattlesnakes, pythons and Gila monsters, along with the associated venom. It is the traditional view that the venom system evolved at one point in the evolutionary tree called Toxicofera. It is believed that the highly venomous snakes called caenophidian snakes came later. The big question that remains is why evolution picked just 24 genes to make highly toxic venom genes when there was over 25,000 to choose from.
More about Snakes, Lizards, toxic venom, evolutionary, housekeeping genes
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