Deficiency of SSTR2a promotes body growth by activating the GH/IGF axis in Nile tilapia Oreochromis niloticus

Le résumé fourni par la source

Somatostatin (SST), named for its ability to inhibit pituitary growth hormone (GH) secretion, is involved in multiple physiological processes though somatostatin receptors (SSTRs). Both in vitro and in vivo studies have demonstrated that SSTR2 mediates GH inhibition by SST. However, whether a deficiency of SSTR2 promotes the somatic growth of fish is unclear. In this study, both sstr2a and sstr2b were predominantly expressed in the pars distalis of the pituitary gland, with sstr2a showing higher expression levels than sstr2b . Mutation of sstr2a was performed in tilapia using the CRISPR/Cas9 system. The sstr2a −/− mutants exhibited a significant increase in body weight at 60, 120, and 180 days post fertilization (dpf) when reared in mixed populations with wild type (WT) fish, being 43 ​% heavier than WT fish at 180 dpf. The sstr2a −/− mutants also demonstrated better growth than WT fish under the separate-tank culture condition, with higher body weight, length, height, and width, weight gain rate, and specific growth rate, as well as lower food intake and feed coefficient, but no difference in condition factor. Furthermore, among female and male sstr2a −/− mutants and WT controls, the growth of male sstr2a −/− mutants was the highest, followed by female sstr2a −/− mutants, then WT males and WT females. No differences were observed between sstr2a −/− mutants and WT fish in the mean area and number of muscle fibers per visual field under the microscope. However, there were fewer lipid droplets in the liver in sstr2a −/− mutants than in WT fish. The deficiency of SSTR2a also led to elevated circulating GH and IGF-1 levels and up-regulated expression of GH/IGF axis genes. Overall, the first established sstr2a −/− mutant line in fish not only holds significant potential to develop into a fast-growth strain of tilapia, but also provides an excellent model for understanding the regulation of growth and metabolism in teleosts.

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