miR-1338-5p Modulates Growth Hormone Secretion and Glucose Utilization by Regulating in Genetically Improved Farmed Tilapia (GIFT, ).

MicroRNAs (miRNAs) are endogenous, non-coding small RNA molecules about 22 nt in length, which could regulate the expressions of target genes and participate in growth and development of organisms. Genetically improved farmed tilapia (GIFT, ) is an important economic freshwater species in China and the growth performance is one of the main breeding indicators. () plays an important role in growth and development of both mammals and invertebrates; however, little studies have been reported on fish. Our previous experiments indicated that miR-1338-5p expression may be negatively correlated with expression. In this study, we firstly used qRT-PCR and northern blot to verify the expression of miR-1338-5p and , and determined the binding site of miR-1338-5p in the 3'-untranslated region (UTR) by luciferase reporter assay. Secondly, juveniles GIFT injected with miR-1338-5p antagomir were used to analyze the regulatory function of the miR-1338-5p- pair . The results showed that the 3'-UTR was complementary to the 5' 2-8-nt site of miR-1338-5p. Inhibition of miR-1338-5p promoted expression in the pituitary and liver of GIFT. could interfere in the growth hormone (Gh)-growth hormone receptor (Ghr)-insulin-like growth factor (Igf) signaling pathway by competing with the for combination with Gh, and then reduce the growth of GIFT. Moreover, the reduction of Gh in serum may regulate insulin secretion and result in the increasing sugar and fat storage in serum and liver. Our results suggest that miR-1338-5p participates in the growth and development of GIFT through the regulation of , which provides theoretical support for the study of the fish growth mechanism.