Unexpected Features Found Via Great White Shark Genome Study
November 20, 2013

Unexpected Features Found Via Great White Shark Genome Study

[ Watch the Video: Genome Of The Great White Shark ]

April Flowers for redOrbit.com - Your Universe Online

Made famous by the horror movie "Jaws," the great white shark is an apex predator that has become an iconic species by capturing an extraordinary amount of public fascination.

What makes this particular shark so distinctive? A new study, published in BMC Genomics, addresses this question by exploring the genetic makeup of this remarkable animal.

A team of scientists from Nova Southeastern University's (NSU) Save Our Seas Shark Research Centre and Cornell University conducted the first large-scale exploration of the great white shark's genetic repertoire, and came up with unexpected findings.

The team compared the transcriptome -- the RNA sequences expressed by the organism's genes -- of the great white shark's heart to the transcriptomes from the zebra fish, which is the best studied fish research model, and humans. They were looking for similarities and significant differences that might explain the distinctiveness of the great white shark. To give the analysis a common comparative base, the team compared gene products that had known functions in all three species.

One surprising result: the proportion of white shark gene products associated with metabolism had fewer differences from humans than from zebra fish (a bony fish).

The team was also surprised to find that aspects of the white shark heart transcriptome, including molecular functions as well as the cellular locations of these functions, also showed greater similarity to humans than to zebra fish. The unexpected results of this study, like many first looks at complex scientific mysteries, raise more questions than provide answers.

"It's intriguing why there are these fewer differences in the proportion of gene products between white sharks and humans, than white sharks and zebra fish," said Mahmood Shivji, PhD, director of NSU's Save Our Seas Shark Research Center and Guy Harvey Research Institute. "One possibility for the apparent greater similarity between white sharks and humans in the proportion of gene products associated with metabolism might be due partly to the fact that the white shark has a higher metabolism because it is not a true cold-bodied fish like bony fishes; however this explanation remains a hypothesis to be further tested."

White sharks are one of the few fishes that are regionally warm-bodied, which means that parts of its body - viscera, locomotor muscles and cranium - are kept at a higher temperature than the surrounding water. This characteristic is known as regional endothermy, and is associated with elevated metabolic rates compared to true cold-blooded bony fishes.

"Additional comparative data from other white shark tissues and/or from other endothermic shark species such as makos would be required to see if this general similarity in gene products holds," said Michael Stanhope of Cornell. "Nevertheless, this preliminary finding opens the possibility that some aspects of white shark metabolism, as well as other aspects of its overall biochemistry, might be more similar to that of a mammal than to that of a bony fish."

The genetic repertoire of the white shark heart had even more curious features. For example, the transcriptome revealed a much lower abundance of a certain type of DNA sequence that occurs in repeated triplet form, than found in other vertebrates. An aberrant increase in the number of such repeated triplet sequences in human genes has been linked to a variety of neurological disorders. Scientists do not know if sharks are immune to neurological genetic diseases, however, the fact that these DNA patterns occur in such low abundance in white shark genes may indicate a reduced chance of similar disorders in this primitive vertebrate.

"Our results, along with other distinctive shark genome features reported by the very few studies in this area by others, are suggesting that we may be in for some surprises as we further explore sharks at their most fundamental level – their genes," said Shivji. "We've just scratched the surface in terms of investigating what makes these evolutionary marvels, and in many cases threatened species, tick."