Elephant shark genome decoded

The genome has explained why sharks have a cartilaginous skeleton and how their immune system is strong despite missing cells previously thought to be key to fighting bacterial and viral infections.
By Ananth Baliga  |  Updated Jan. 8, 2014 at 2:23 PM
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The first shark genome decoded belongs to the slow-evolving elephant shark, providing researchers new insight into cartilaginous fish, and the differences between sharks and other bony vertebrates.

A team of international researchers, including researchers from the Max Planck Institute of Immunobiology and Epigenetics and San Francisco State University, have decoded the one billion DNA pairs found in the elephant shark genome and compared them to the 3 billion DNA pairs found in humans.

The findings, published in Nature, have given them a better understanding of why a shark's skeleton is largely composed of cartilage rather than bone, and why their immune system is simpler than that of humans.

The researchers found a family of genes missing that are critical for bone formation and found in most bony vertebrates. This family of genes enables other vertebrates to replace cartilage with bone and researchers believe they could use this data to better understand bone diseases like osteoporosis.

Analysis of genes linked to the immune system showed that sharks lacked T-helper lymphocytes, which until now were considered essential for fighting off viral and bacterial infections. But despite the absence of these lymphocytes the shark has a robust immune defense system.

“It is obvious that sharks can efficiently deal with all kinds of infections without this particular cell type. This indicates that nature can come up with different solutions to the same problem,” said Thomas Boehm, co-author and director at the Max Planck Institute of Immunobiology and Epigenetics in Freiburg.

The study also provided evidence that elephant shark genome is the slowest evolving among all vertebrates. The study of a shark's genome is considered essential because they are the oldest living group of jawed-vertebrates that diverged from bony vertebrates about 450 million years ago.

[Max Planck Institute of Immunobiology and Epigenetics] [Nature]

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