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Nov 20, 2013

Shark Transcriptome Less Fishy, More Human Than Expected

  • Researchers primarily interested in conserving the great white shark undertook a gene-level analysis of the remarkable creature, which remains mysterious even though it continues to hold the public’s imagination as firmly as its jaws seize prey. After completing their work, the researchers found that the mystery of the great white had only deepened, since they had established that in some respects, at the genetic level, the great white resembles humans more closely than bony fishes.

    Given the difficulties inherent in collecting suitable tissues from great white sharks, the researchers had to limit their study to one type of tissue, from a single shark. Nonetheless, the tissue sample, from the shark’s heart, proved to be revealing.

    Combining Roche-434 and Illumina sequencing technologies, the researchers compared the transcriptome from the white shark’s heart to the transcriptomes from humans and the zebrafish, the best-studied fish research model. Surprisingly, the researchers found that the proportion of white shark gene products associated with metabolism had fewer differences from humans than zebrafish.

    This result appeared in BMC Genomics, in a paper entitled “Characterization of the heart transcriptome of the white shark (Carcharodon carcharias).” Besides describing the unexpected gene-level similarities between the great white and humans, the authors of this paper write, “The transcriptome resource also provides a large set of new microsatellites that will be immediately useful as markers in studies of population structure, dispersal dynamics, genetic diversity, and mating system biology to further the conservation and management of this vulnerable species.”

    In considering possible explanations for the shark genome’s human-like gene products, study co-author Mahmood Shivji, Ph.D., director of Nova Southeastern University’s Save Our Seas Shark Research Center and Guy Harvey Research Institute, said, “One possibility [might be 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.”

    One of the notable biological properties of white sharks is that it is one of few fishes that is regionally warm-bodied, that is, parts of its body (its viscera, locomotor muscles and cranium) are kept at a higher temperature than the surrounding water world—a property known as regional endothermy. This warm-body property is in turn 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, Ph.D., an evolutionary biologist at Cornell University who co-led the study with Dr. Shivji. “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.”



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