Effects of vitamin B₂ on the gonad growth, texture traits, collagen content and related gene expression of sea urchin (Mesocentrotus nudus)

The market value of sea urchin gonads is determined by the specific characteristics associated with gonad size and texture. The objective of this study was to investigate the impact of vitamin B₂ on the gonad growth, texture, collagen content, and the expression of genes involved in the collagen synthesis of sea urchins (Mesocentrotus nudus). Graded amounts of vitamin B₂ (0, 15 and 30 mg/kg) were supplemented to make three formulated feeds. Fresh kelp (Saccharina japonica) was used as the control group. Each diet was randomly distributed to three tanks of M. nudus initial body weight: (3.63 ± 0.02) g. The results indicated that the gonadosomatic index (GSI) and texture traits (hardness, springiness, adhesiveness, gumminess and water content) of M. nudus fed kelp were significantly lower than those fed formulated feeds. The GSI and texture traits of M. nudus fed 15 mg/kg vitamin B₂ were significantly greater than those fed 0 and 30 mg/kg vitamin B₂. The gonad collagen content of sea urchins fed 15 mg/kg vitamin B₂ was significantly higher than those fed kelp, 0 and 30 mg/kg vitamin B₂. The expression levels of collagen synthesis genes (collagen protein alpha-1, 2 and 3) and transforming growth factor beta (TGF-β)/Sma- and Mad-related protein (Smad) pathway genes (TGF-β receptor 1 and 2, smad nuclear-interacting protein 1 (SNIP1) and prolyl 4-hydroxylase subunit beta (P4Hβ)) of M. nudus fed 15 mg/kg vitamin B₂ were significantly higher than those fed 0 and 30 mg/kg vitamin B₂. On the contrary, the expression levels of collagen degradation genes (lysyl oxidase-like 2 (LOXL2) and matrix metalloproteinase 14 (MMP14)) in the 15 mg/kg vitamin B₂ group were significantly lower than those in the 0 and 30 mg/kg vitamin B₂ and kelp groups. In conclusion, vitamin B₂ at an addition level of 15 mg/kg significantly increased the gonad texture and collagen contents of M. nudus, which could be accomplished by increasing collagen synthesis and inhibiting collagen degradation through the TGF-β/Smad pathway. These results could contribute to better understanding the beneficial effects of vitamin B₂ addition on the gonad texture quality of M. nudus.