The Influence of Diet Containing Wheat Gluten Supplemented with Dipeptides or Amino Acids on the Morphology of White Muscle of Yellow Perch (Perca flavescens)

Insights into Dietary Different Co-Forms of Lysine and Glutamate on Growth Performance, Muscle Development, Antioxidation and Related Gene Expressions in Juvenile Grass Carp (Ctenopharyngodon idellus)

The study aimed to compare the effects of crystalline L-lysine and L-glutamate (CAA), Lys-Glu dipeptide (KE) on the growth and muscle development of grass carp (Ctenopharyngodon idellus), and related molecular mechanisms. Five experimental diets (CR, 0.5% CAA, 1.5% CAA, 0.5% KE, 1.5% KE) containing Lys and Glu as free (Lys and Glu, CAA) dipeptide (Lys-Glu, KE) forms were prepared, respectively. A total of 450 juvenile grass carp with an initial weight of 10.69 ± 0.07 g were randomly assigned to 15 cages, and 5 treatments with 3 replicates of 30 fish each for 61 days of feeding. The results showed that the group of 0.5% KE exhibited the best growth performances according to the indicator's weight gain rate (WGR) and specific growth rate (SGR), although no statistically significant occurred among all groups; diet supplemented with 0.5% CAA significantly elevated the condition factor (CF) and viscerasomatic index (VSI) of juvenile grass carp. Diet supplemented with different Lys and Glu co-forms at different levels promoted the muscle amino acid content compared with those of CR group. Comparing with the CR group and other groups, the hardness of 0.5% CAA group significantly increased, and the springiness of 0.5% KE group excelled. Both the muscle fiber diameter and density of 0.5% KE group showed significant difference with those of the CR group, and a negative correlation between them was also observed. To uncover the related molecular mechanism of the differences caused by the different co-forms of Lys and Glu, the effect of different diets on the expressions of protein absorption, muscle quality, and antioxidation-related genes was analyzed. The results suggested that comparing with those of CR group, the dipeptide KE inhibited the expressions of genes associated with protein metabolism, such as AKT, S6K1, and FoxO1a but promoted PCNA expression, while the free style of CAA would improve the FoxO1a expression. Additionally, the muscle development-related genes (MyoD, MyOG, and Myf5) were significantly boosted in CAA co-form groups, and the expressions of fMYHCs were blocked but fMYHCs30 significantly promoted in 0.5% KE group. Finally, the effect of different co-forms of Lys and Glu on muscle antioxidant was examined. The 0.5% CAA diet was verified to increase GPX1a but obstruct Keap1 and GSTP1 expressions, resulting in enhanced SOD activity and reduced MDA levels in plasma. Collectively, the different co-forms of Lys and Glu influenced the growth of juvenile grass carp, and also the muscle development and quality through their different regulation on the protein metabolism, muscle development- and antioxidative-related genes.

The Role of Transcription Factors in Gonad Development and Sex Differentiation of a Teleost Model Fish-Guppy (Poecilia reticulata)

The guppy (Poecilia reticulata) is one of the world's most popular ornamental fish. Due to lecithotrophic viviparous, it is commonly used in toxicological studies and environmental monitoring. This study aimed to investigate the molecular mechanisms of gonad development and differentiation during guppy ontogenesis. The study mainly focused on the role and localization of potential specific sex markers and transcription factors: Sox9, Dmrt1, Erβ. For histological analysis, guppies of both sexes were collected at 1, 60, and 360 dph (day post-hatching). The gonads morphology and immunohistochemistry detection of mentioned markers localization were performed. The expression of Sox9 protein was compared between sexes. Histological analysis revelated all types of male germinal cells in 60 dph guppy's testes. Maturated oocytes were visible in the ovaries of 360 dph fish. The Sox9 expression varied in spermatocytes and spermatids, from cellular to nuclear localization, and was higher in ovaries. Dmrt1 was detected in all testes groups and 360 dph ovaries. The Erβ was observed in both sexes at 60 and 360 dph. For the first time, the localization of transcription factors in guppy during ontogenesis was traced. The Sox9 designation as a factor regulating the development of germinal cells in adult guppies may facilitate the analysis of xenobiotics' influence on fish's reproductive system.