Scientists decode elephant shark genome

A team of researchers has sequenced the genome of the elephant shark, a curious-looking fish with a snout resembling the end of an elephant's trunk.

The elephant shark and its cousins the sharks, rays, skates and chimaeras are the world's oldest-living jawed vertebrates. But their skeletons are made of cartilage rather than bone, making this group of vertebrates an oddity on the evolutionary tree.

Senior author Wesley Warren, PhD, research associate professor of genetics at The Genome Institute at Washington University School of Medicine, said that they now have the genetic blueprint of a species that is considered a critical outlier for understanding the evolution and diversity of bony vertebrates, including humans.

Among the cartilaginous fishes, the elephant shark was selected for sequencing because of its compact genome, which is one-third the size of the human genome.

By analyzing the elephant shark genome and comparing it with other genomes, the scientists discovered a family of genes that is absent in the elephant shark but present in all bony vertebrates, including the chicken, cow, mouse and human.

When the researchers deleted a member of this gene family in zebrafish, they observed a reduction in bone formation, highlighting the gene family's significance in making bone.

In a surprise finding, the team found that the elephant shark appears to lack special types of immune cells that are essential to mounting a defense against viral and bacterial infections and for preventing autoimmune diseases such as diabetes and rheumatoid arthritis.

Furthermore, large chunks of elephant shark and human chromosomes were found to be highly similar.

The research has been published in the journal Nature.