An international team of researchers has sequenced and analyzed the genome of the king cobra (Ophiophagus hannah). The team has also sequenced the genome of the Burmese python (Python molurus bivittatus) and compared it with that of the cobra.
King cobra, Ophiophagus hannah. Image credit: Anand Titus / Geeta Pereira / Michael Allen Smith / CC BY-SA 2.0.
The Burmese python’s ability to ramp up its metabolism and enlarge its organs to swallow and digest prey whole can be traced to unusually rapid evolution and specialized adaptations of its genes and the way they work.
The python study, published in the Proceedings of the National Academy of Sciences, calls into question previous theories that major obvious physical differences among species are caused primarily by changes in gene expression. Instead, it contends that protein adaptation, gene expression and changes in the structure of the organization of the genome itself are all at work together in determining the unusual characteristics that define snakes, and possibly other vertebrates.
The king cobra study, also published in the Proceedings of the National Academy of Sciences, provides insight into the biology of the venom in snakes, and allow the understanding of the evolution of venom genes at the genome structural level.
Armed with the both the king cobra and Burmese python genome, the scientists were able to show that, despite previous hypotheses that venom genes evolve early in the lineage leading to snakes, venom gene families do not duplicate early. In fact, the two studies show that the rapid and extensive expansion of functionally important venom toxin families is restricted to the venomous advanced snake lineage.
Burmese python, Python molurus bivittatus. Image credit: Tim Vickers.
The diversification of these toxins correlates directly with their functional importance in prey capture, for example the most pathogenic king cobra toxin family has undergone massive expansion, while, in contrast, venom proteins with less important functions do not participate in the evolutionary arms race occurring between snakes and their prey.
“These are the first snake genomes to be sequenced and fully annotated and our results in relation to the king cobra provide a unique view of the origin and evolution of snake venom, including revealing multiple genome-level adaptive responses to natural selection in this complex biological weapon system,” explained co-author Dr Nicholas Casewell from Bangor University and Liverpool School of Tropical Medicine.
“These adaptations include the massive and rapid expansion of gene families that produce venom toxins, providing the snake with a highly toxic protein mixture required to overcome a variety of different prey and also circumvent any resistance to venom that may have developed in such prey.”
The python and king cobra studies represent a significant addition to the field of comparative systems genomics – the evolutionary analysis of multiple vertebrate genomes to understand how entire systems of interacting genes can evolve from the molecules on up.
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Castoe TA et al. The Burmese python genome reveals the molecular basis for extreme adaptation in snakes. PNAS, published online December 2, 2013; doi: 10.1073/pnas.1314475110
Vonk FJ et al. The king cobra genome reveals dynamic gene evolution and adaptation in the snake venom system. PNAS, published online December 2, 2013; doi: 10.1073/pnas.1314702110
