New model for snake venom evolution

Researchers have found genetic evidence that highly toxic venom proteins were evolutionarily ‘born’ from non-toxic genes, which have other ordinary jobs around the body, such as regulation of cellular functions or digestion of food. Technology that can map out the genes at work in a snake or lizard’s mouth has, in many cases, changed the way scientists define an animal as venomous. If oral glands show expression of some of the 20 gene families associated with “venom toxins,” that species gets the venomous label. Researchers found similar levels of these so-called toxic gene families in python oral glands and in tissue from the python brain, liver, stomach and several other organs.  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 till now everything was focused in the venom gland, where venom is produced before it is injected. There was no examination of other parts of the snake’s body. This is the first study to have used the genome. These potentially venomous genes end up in the oral gland by default, because they are expressed in low but consistent ways throughout the body. Then, because of natural selection on this expression in the oral gland being beneficial, tissues in the mouth begin expressing those genes in higher levels than in other parts of the body. Finally, as the venom evolves to become more toxic, the expression of those genes in other organs is decreased to limit potentially harmful effects of secreting such toxins in other body tissues.