Mola Mola’s Genome May Explain Its Gigantic Size

Researchers have sequenced the genome of the ocean sunfish, focusing particularly on growth hormone signalling genes to understand its freakish growth spurts.

AsianScientist (Sep. 12, 2016) – Researchers in Singapore and China have sequenced the genome of the ocean sunfish (Mola mola), the world’s largest bony fish. Their results have been published in the journal GigaScience.

The ocean sunfish, which can be found in tropical and temperate sea zones such as the Mediterranean or the Atlantic, can grow up to a length of 2.7 meters and weigh 2.3 tons. The sunfish grows at an unusually fast rate of almost one kilogram per day; other fishes grow at 0.02 to 0.5 kilograms per day. Furthermore, females can produce more eggs than any other known vertebrate—up to 300,000,000 at a time.

Its genome, which was sequenced by study leader Dr. Byrappa Venkatesh at Singapore’s Agency for Science, Technology and Research (A*STAR), along with colleagues at the China National Genebank (CNGB), revealed several altered genes that may explain the fish’s fast growth rate and large size, as well as its unusual endoskeleton and unique body shape.

Before the study was carried out, the researchers hypothesized that the sunfish’s unusual appearance may be due to the loss of HOX genes. These genes control the body plan of an organism on the head-tail axis by specifying which parts of the body—such as head, thorax or abdomen—the different segments of an embryo will form. They were surprised to find out that this wasn’t the case, discovering instead that the sunfish possessed complete HOX gene clusters.

“We found that several genes involved in growth hormone signalling evolve very fast in the sunfish when compared to other bony fishes, which may explain its large size and fast growth rate,” said corresponding author Dr. Zhang Guojie, the associate director of CNGB.

The article can be found at: Pan et al. (2016) Genome of the Ocean Sunfish (Mola mola).


Source: GigaScience; Photo: Wikipedia.
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