Dietary protein regulates ovarian development through TOR pathway mediated protein metabolism in female Litopenaeus vannamei

Abstract

The accumulation of nutrients in the gonads is closely related to reproductive capacity and quality of the larvae in the subsequent autotrophic stage of Pacific white shrimp, Litopenaeus vannamei. Nutrition is one of the important factors affecting the gonad development of aquaculture animals, dietary protein is utilized as the major component of vitellogenin through vitellogenesis, which acts as an indispensable nutrient in ovary development. Therefore, six different protein diets were formulate to contain 39.81%, 44.34%, 48.20%, 52.81%, 56.12% and 59.45%, respectively. A total of 540 shrimp (initial weight, 9.3 g) were distributed randomly into eighteen 250-L cylindrical fiber-glass tanks, with each diet assigned to 3 replicate tanks. The results showed Arg, His, Leu, Lys, Glu, Gly, Pro, total essential amino acids (ΣEAA) and total non-essential amino acids (ΣNEAA) in ovary were significantly influenced by dietary protein levels, and shrimps fed diet with 39.81% protein exhibited the lowest total amino acids composition in ovary among all treatments. The percentage of ovarian development in stages III-V was higher in shrimp fed diets with higher protein ( ≥ 48.20%) than those fed diets with lower protein. Shrimp fed diet with 52.81% protein had higher serum concentrations of vitellogenin (VTG), meanwhile, shrimp fed the diet with 52.81% protein had higher expression levels of vitellogenin 1 (vg1), vtg and vitellogenin receptor (vgr) in the ovaries than those fed the other diets. However, the highest concentrations of VTG in the hepatopancreas and ovaries were observed at shrimp fed diet with 52.81% protein. The expression levels of target of rapamycin (torc1), ras homologue enriched in brain (rheb), protein kinase B (akt), 4E-binding protein (4ebp) and phosphatidylinositol 3-kinase (pi3k) in ovary and hepatopancreas significantly up-regulated in shrimp fed diet with 52.81% protein. In conclusion, dietary 52.81% protein promoted the synthesis of exogenous vitellogenin in hepatopancreas and its transport to the ovary through serum, and also motivated the production of endogenous vitellinogen in ovary, and was involved in the regulation of ovarian development through TOR mediated protein metabolism of L.vannamei .