Abstract
Teleost fish can synthesize one of the major omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFAs), docosahexaenoic acid (DHA, 22:6n-3), from dietary α-linolenic acid (ALA; 18:3n-3), via elongase of very long–chain fatty acid (Elovl) and fatty acid desaturase (Fads). However, it remains unclear which elongase is primarily responsible for the endogenous synthesis of DHA. Here, in this study, the knockout models of the two major elongases, Elovl2 and Elovl5, were generated by CRISPR/Cas9 approach in zebrafish and comparatively analyzed. The homozygous mutants were validated by Sanger sequencing, mutation-mediated PCR, and whole-mount in situ hybridization analysis of the endogenous target genes. Compared with wild-type (WT) counterparts, the content of DHA was significantly reduced by 67.1% (P < 0.05) in the adult liver and by 91.7% (P < 0.01) in the embryo at 3-day post-fertilization (dpf) of the elovl2 mutant, but not of the elovl5 mutant. Further study revealed that elovl2 and fads2 was upregulated by 9.9-fold (P < 0.01) and 9.7-fold (P < 0.01) in the elovl5 mutant, and elovl5 and fads2 were upregulated by 15.1-fold (P < 0.01) and 21.5-fold (P < 0.01) in the elovl2 mutant. Our study indicates that although both Elovl2 and Elovl5 have the elongase activity toward C20, the upregulation of elovl2 could completely replace the genetic depletion of elovl5, but upregulation of elovl5 could not compensate the endogenous deficiency of elovl2 in mediating DHA synthesis. In conclusion, the endogenous synthesis of DHA in is mediated by Elovl2 but not Elovl5 in zebrafish and a DHA-deficient genetic model of zebrafish has been generated.
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Funding
The National Key R&D Program of China (grant No 2018YFA0801000), the National Natural Science Foundation of China (grant No 31972780), the Youth Innovation Promotion Association of Chinese Academy of Sciences, and the State Key Laboratory of Freshwater Ecology and Biotechnology (grant number 2019FBZ05).
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Y. S. designed the study and has primary responsibility for the final content; C. L. and D. Y. conducted research; C. L., D. Y., and Y. S. analyzed the data and wrote the manuscript; and H. W. and M. H. provided resources necessary to complete experiments. All authors read and approved the final manuscript.
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The experiments involving zebrafish followed the Zebrafish Usage Guidelines of CZRC and were performed under the approval of the Institutional Animal Care and Use Committee of the Institute of Hydrobiology, Chinese Academy of Sciences, under protocol IHB2015–006.
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Liu, C., Ye, D., Wang, H. et al. Elovl2 But Not Elovl5 Is Essential for the Biosynthesis of Docosahexaenoic Acid (DHA) in Zebrafish: Insight from a Comparative Gene Knockout Study. Mar Biotechnol 22, 613–619 (2020). https://doi.org/10.1007/s10126-020-09992-1
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DOI: https://doi.org/10.1007/s10126-020-09992-1