Abstract
The histological integrity of the intestine depends on the tight and orderly arrangement of epithelial cells within the intestinal villi. Nodal, a transforming growth factor-β (TGF-β) family member, has been reported to promote epithelial cell proliferation. Collagen not only establishes physical connections between adjacent cells but also serves as an anchoring platform for cell adhesion and regeneration processes. Therefore, a 21-day feeding trial was conducted using RNA interference to investigate the role of the Nodal gene in regulating intestinal collagen synthesis and histological structure integrity in juvenile A. japonicus fed diets containing graded levels of vitamin E (VE) (0, 200, and 400 mg/kg). The results showed that the addition of 200 mg/kg VE significantly improved the growth rate, immune enzyme activities and related gene expression, as well as intestinal villus morphology. Additionally, the addition of 200 mg/kg VE upregulated the expression of Nodal, which activated the expression of collagen synthesis-related genes and promoted collagen deposition in the intestines of A. japonicus. After Nodal gene knockdown, A. japonicus presented a decreased growth rate, damage to the intestinal histological structure, and impaired collagen synthesis, with the most notable findings observed in A. japonicus fed diets without VE addition. However, these detrimental effects were eliminated to some extent by the addition of 200 mg/kg VE. These findings indicate that VE improves immune function and intestinal histological structure in A. japonicus through a Nodal-dependent pathway.