The osteobic fish genome resolves the mystery of the origin of fish thermostatics

In the evolution of vertebrates, temperature has an important regulatory effect on the physiological activities of living organisms. Birds and mammals on land are able to adapt to a variety of habitats, and their ability to keep temperatures at bay is a credit to it. Compared with the terrestrial environment, it is more difficult for organisms in the aquatic environment to obtain constant temperature capacity, and they must face the challenge of high specific heat and easy loss of heat in water. However, according to observations, at least 40 species of fish have overcome these difficulties and have a constant temperature capacity similar to that of mammals and birds. Among them, swordfish, sailfish and tuna are two representative of thermostatic bony fish. How these fish overcame difficulties and eventually evolved their thermostatic capacity is a mystery that remains unsolved.

Recently, the Institute of Deep-sea Sciences and Engineering of the Chinese Academy of Sciences and Northwestern Polytechnical University collaborated on research, and published a paper on Molecular Biology and Evolution The genomes of two billfishes provide insights into the evolution of endothermy in teleosts, and published high-quality swordfish and sailfish genomes. And analyzed their constant temperature mechanism.

Fish temperature constant temperature is a relatively rare phenomenon, and about 40 of the existing about 40,000 fish species have constant temperature capacity. Through continuous swimming, they generate heat, maintain a constant temperature, and eventually evolve into thriving taxa among fish. Swordfish of independent origin - sailfish and tuna are two of these species of fish. Is there a similar molecular mechanism for this phenotypic convergence? The study found that there are four genes with significant convergence signals (pkmb, ryr1a, atp2a1 and rh1) in swordfish-sailfish and tuna, of which pkmb, ryr1a and atp2a1 are in the invalid calcium ion circulation pathway associated with red muscle thermogenesis, so that the energy released by decomposition ATP is not used for the transmembrane circulation of calcium ions, but for heat generation. The pkmb-encoded pyruvate kinase is the last step of the glycolysis process, and there are two convergence sites in swordfish-sailfish and tuna, and the mutation of this site has been shown to change the efficiency of ATP production during glycolysis. These alterations in convergent genes may be the molecular basis for heat production in eukeletal fish.

In order to cope with the rapid heat dissipation of water bodies, aquatic thermostatic animals usually have a unique countercurrent exchanger for the preservation and transfer of temperature. Swordfish and sailfish have a vascular network system in which arterial and venous vessels are arranged in parallel and the blood flow direction is completely opposite. In homologous gene analysis of swordfish and sailfish, it was found that there were 9 genes that were significantly positively selected, and three genes (dapk3, prkcda and rfx4) had large amino acid changes. Dapk3 is an important factor in the regulation of smooth muscle contraction in vertebrate animals, and this gene may be involved in the formation of vascular networks; prkcda is an important gene that regulates vascular tone, which may promote the better realization of heat preservation and transfer in countercurrent exchangers. Rfx4 is highly expressed in the mammalian suprachiasmphalus and has a regulatory effect on diurnal changes and temperature stimulation. Significant changes in this gene in swordfish and sailfish suggest that the suprachiasmphalus may also have a key regulatory effect on them.

In addition, it was found that rh1 associated with visually sensitive types was convergent and replaced in sailfish, swordfish and tuna, and gene doubling and positive selection occurred in prdm1 and rp2 associated with photoreceptor development, respectively; chd9 associated with maxillary development was missing regulatory elements upstream or promoting the development of swordfish and swordfish maxillas, and changes in the structure of the ggps1 protein may be related to the rapid repair ability of their maxilla The loss of regulatory elements in the hox gene family may be related to the development of the dorsal fin of the sailfish and the loss of the ventral fin of the swordfish.

Wu Baosheng, a doctoral student at the Institute of Deep Sea, is the first author of the paper, and He Shunping, a researcher at the Institute of Deep Sea, and Wang Kun, associate professor of Northwestern Polytechnical University, are the corresponding authors of the paper.

Thermostatic pathways associated with swordfish and sailfish and phenotypic-related genetic changes

Source: Institute of Deep-Sea Science and Engineering, Chinese Academy of Sciences

Source: Voice of the Chinese Academy of Sciences