Hailin Pan1,*, Hao Yu1,*, Vydianathan Ravi2,*, Cai Li1, Alison P. Lee2, Michelle M. Lian2, Boon-Hui Tay2, Sydney Brenner2, Jian Wang3, Huanming Yang3, Guojie Zhang1,† and Byrappa Venkatesh2,4,†
1 China National Genebank, BGI-Shenzhen, Shenzhen 518083, China.
2 Institute of Molecular and Cell Biology, A*STAR, Biopolis, Singapore 138673.
3 BGI-Shenzhen, Shenzhen 518083, China.
4 Department of Paediatrics, Yong Loo Lin School of Medicine, National University of Singapore,
* Joint first authors
† Corresponding authors
Published in GigaScience on 9 September 2016.
Media report about this paper: https://www.sciencedaily.com/releases/2016/09/160908203903.htm
Blog on ocean sunfish genome: http://blogs.biomedcentral.com/gigablog/2016/09/12/big-fish-small-genomes-ocean-sunfish-shines/
The ocean sunfish (Mola mola; Order Tetraodontiformes), which can grow up to a length of 2.7 m and weigh 2.3 tons, is the world’s largest bony fish. Although it belongs to the same Order as that of pufferfish, its morphology differs dramatically from that of pufferfish. The ocean sunfish has an extremely fast growth rate and its endoskeleton is mainly composed of cartilage. It also lacks a caudal fin, which is replaced by a broad and stiff lobe that results in the characteristic truncated appearance of the fish. To gain insights into the genomic basis of these phenotypic traits, we sequenced the sunfish genome and performed comparative analyses with other teleost genomes. Several sunfish genes involved in the growth hormone and insulin-like growth factor 1 (GH/IGF1) axis signalling pathway were found to be under positive selection or accelerated evolution, which might explain its fast growth rate and large body size. A number of genes associated with the extracellular matrix, some of which are involved in the regulation of bone and cartilage development, have also undergone positive selection or accelerated evolution. A comparison of the sunfish genome with that of the pufferfish (fugu), which has a caudal fin, revealed that the sunfish contains more homeobox (Hox) genes than pufferfish. Thus, caudal fin loss in sunfish is not associated with the loss of a specific Hox gene. Our analyses provide insights into the molecular basis of the fast growth rate and large size of the ocean sunfish. The high-quality genome assembly generated in this study should facilitate further studies of this ‘natural mutant’.
Figure: (a) An ocean sunfish. Photo courtesy: Chang Ai-Lien (b) Phylogenetic relationship of the ocean sunfish with other fishes based on a phylogenomic approach. The scale bar shows divergence time estimates (MYA, million years ago) and the blue bars represent the 95% confidence intervals for the estimates. Values at the nodes represent bootstrap support percentages. The ocean sunfish lineage diverged from the pufferfish lineage approximately 68 million years ago.
For more information on Byrappa VENKATESH 's lab, please click here.