Characterization of Pax3 and Pax7 genes and their expression patterns during different development and growth stages of Japanese pufferfish Takifugu rubripes

Transcriptome analyses of betta fish (Betta splendens) provide novel insights into fin regeneration and color-related genes

The betta fish (Betta splendens), an important ornamental fish, haswell-developed and colorful fins.After fin amputation, betta fish can easily regenerate finssimilar to the originalsin terms of structureand color. The powerful fin regeneration ability and a variety of colors in the betta fish are fascinating. However, the underlying molecular mechanisms are still not fully understood. In this study, tail fin amputation and regeneration experiments were performed on two kinds of betta fish: red and white color betta fish. Then, transcriptome analyseswere conducted to screen out fin regeneration and color-relatedgenes in betta fish. Through enrichment analyses of differentially expressed genes (DEGs), we founda series of enrichment pathways and genes related to finregeneration, including cell cycle (i.e. plcg2), TGF-beta signaling pathway (i.e. bmp6), PI3K-Akt signaling pathway (i.e. loxl2aand loxl2b), Wnt signaling pathway(i.e. lef1), gap junctions (i.e. cx43), angiogenesis (i.e. foxp1), and interferon regulatory factor (i.e. irf8). Meanwhile, some fin color-related pathways and genes were identified in betta fish, especially melanogenesis (i.e. tyr, tyrp1a, tyrp1b, and mc1r) and carotenoid color genes (i.e. pax3, pax7, sox10, and ednrba). In conclusion, this studycan not only enrich the research onfish tissue regeneration, but also has a potential significance for the aquaculture and breeding of the betta fish.

Characterization and functional analysis of pax3 in body color transition of polychromatic Midas cichlids (Amphilophus citrinellus)

As the representative genetic and economic trait of ornamental fish, skin color has a strong impact on speciation and adaptation. However, the genetic basis of skin color pigmentation, differentiation and change is still not understood. The Midas cichlid fish with three typical body color transition stages of "black-gray‑gold" is an ideal model system for investigating the formation and change of fish body color. In this study, to investigate the regulatory role of the pair box 3 (pax3) gene in the early body color fading process of Midas cichlids, the complete cDNA sequence (3513 bp) of pax3 was successfully isolated from Midas cichlids (Amphilophus Citrinellus), and found to encode polypeptides of 491 amino acids. Expression patterns of the pax3 gene in tissues of Midas cichlids during different periods, including embryonic development and body color fading stages were detected by quantitative real-time PCR. The qRT-PCR analysis showed that pax3 was expressed in all tissues of adult fish, with a higher expression level in muscle and skin. The highest expression level in muscle tissue was significantly higher than that in other tissues (P < 0.05). During embryonic development, the expression tendency of pax3 was first increased and then decreased. In the three typical stages of early skin color fading from black to gold, pax3 expression in skin, caudal fin and scales all showed a downward trend. The expression level in the black stage was significantly higher than that in other stages (P < 0.05). Positive signal of pax3 protein was detected in the three typical skin color conversion stages, and the highest positive signal intensity was detected in the black stage, which was consistent with qRT-PCR results. After pax3 RNA interference, pax3 and the downstream genes mitf and tyr all decreased, while dct mRNA expression increased in the skin of fish. Western blotting also showed a decrease in pax3 protein concentration. Those results suggest that pax3 plays an important role in skin color formation, distribution and change in Midas cichlids through the melanogenesis pathway.

Molecular characterization of Pax7 and its role in melanin synthesis in Crassostrea gigas

The paired-box 7 (Pax7) is a transcription factor crucial for skin color polymorphism. However, the mechanism underlying the pigmentation associated with Pax7 in mollusks have yet to be elucidated. In this study, the cDNA sequence of Pax7 in the Pacific oyster Crassostrea gigas (CgPax7) was characterized. Phylogenetically, the identity of deduced amino acid sequence was similar to that of other mollusks and contained 463 amino acids, with conserved features of paired domain (PRD), homeobox domain (HD) and octapeptide. Gene expression analysis revealed that CgPax7 was markedly increased at D-shaped larvae stage and ubiquitously expressed in six examined tissues in adult oyster. The result of whole-mount in situ hybridization (WMISH) showed a restricted pattern of CgPax7 expression on margins of shell valves at D-shaped and umbo larvae stages. Additionally, although CgPax7 silencing had no significant effect on CgMitf expression, it significantly inhibited the expressions of CgPax7, CgTyr, CgTyrp1, CgTyrp2 and CgCdk2, genes involved in Tyr-mediated melanin synthesis. Furthermore, CgPax7 knockdown obviously decreased the tyrosinase activity. Less brown-granules at mantle edge was detected by micrographic examination and melanosomes defect was observed by transmission electron microscopy. It was demonstrated that CgPax7 play a key role in melanin synthesis by regulating Tyr-pathway in C. gigas. These findings indicated the potential framework by which mollusks pigmentation.

Effects of Dietary Paper Mulberry (Broussonetia papyrifera) on Growth Performance and Muscle Quality of Grass Carp (Ctenopharyngodon idella)

Simple Summary

The quality of muscle plays an important role in improving the economic benefit of aquatic products. The paper mulberry (Broussonetia papyrifera, BP) grows wildly in the south of Asia. In this experiment, grass carps (initial weight: 50.0 ± 0.5 g) were fed diets with the addition of 0%, 5%, 10%, 15% and 20% BP in a control diet (crude protein: 31%, crude fat: 3.8%) for 8 weeks. In conclusion, adding 5% BP did not affect the growth of grass carp. However, the supplementation of 10% BP could improve muscle quality through improving muscle hardness, reducing fat accumulation and muscle fiber diameter, at the cost of reducing growth performance.

Abstract

The present study investigated the effects of dietary paper mulberry (Broussonetia Papyrifera, BP) on growth performance, muscle quality and muscle growth-related mRNA expressions of grass carp. Fish (initial weight: 50.0 ± 0.5 g) were fed diets supplemented with 0% (control diet), 5%, 10%, 15% and 20% BP for 8 weeks. The results showed that increasing levels of paper mulberry linearly and quadratically decreased the special gain rate (SGR) and increased the feed conversion rate (FCR) of grass carp (p < 0.05). Significantly positive quadratic trends were found between paper mulberry levels and muscle crude fat or crude protein of grass carp (p < 0.05). In comparison to the control diet, the 10%BP and 15%BP groups had significantly decreased muscle crude fat and increased crude protein (p < 0.05). The levels of paper mulberry resulted in a linear and quadratic increase in water loss of grass carp muscle (p < 0.05), and all groups with paper mulberry supplementation were significantly higher than the control group (p < 0.05). Significant positive linear and quadratic trends were found between the paper mulberry levels and muscle fiber diameter or density of grass carp (p < 0.05). In comparison to the control diet, the significant differences were found in the 15%BP and 20%BP groups (p < 0.05). The muscle adhesiveness and hardness linearly and quadratically increased with the increasing levels of paper mulberry (p < 0.05), and both of which increased significantly when the level of paper mulberry reached 10% (p < 0.05). In addition, the increase in paper mulberry linearly and quadratically improved the expressions of myoblast determination protein (MyoD), myogenin (MyoG), paired box protein 7 (Pax7) and myostatin 1 (MSTN1) (p < 0.05). When the supplementation of paper mulberry reached 15%, the expressions of all these mRNAs were significantly higher than those of the control group (p < 0.05). In summary, adding 5% paper mulberry did not affect the growth of grass carp. However, the supplementation of 10% paper mulberry could improve muscle quality through improving muscle hardness, reducing fat accumulation and muscle fiber diameter, at the cost of reducing growth performance.

Pax3 and Pax7 Exhibit Distinct and Overlapping Functions in Marking Muscle Satellite Cells and Muscle Repair in a Marine Teleost, Sebastes schlegelii

Pax3 and Pax7 are members of the Pax gene family which are essential for embryo and organ development. Both genes have been proved to be markers of muscle satellite cells and play key roles in the process of muscle growth and repair. Here, we identified two Pax3 genes (SsPax3a and SsPax3b) and two Pax7 genes (SsPax7a and SsPax7b) in a marine teleost, black rockfish (Sebastes schlegelii). Our results showed SsPax3 and SsPax7 marked distinct populations of muscle satellite cells, which originated from the multi-cell stage and somite stage, respectively. In addition, we constructed a muscle injury model to explore the function of these four genes during muscle repair. Hematoxylin–eosin (H–E) of injured muscle sections showed new-formed myofibers occurred at 16 days post-injury (dpi). ISH (in situ hybridization) analysis demonstrated that the expression level of SsPax3a and two SsPax7 genes increased gradually during 0–16 dpi and peaked at 16 dpi. Interestingly, SsPax3b showed no significant differences during the injury repair process, indicating that the satellite cells labeled by SsPax3b were not involved in muscle repair. These results imply that the muscle stem cell populations in teleosts are more complicated than in mammals. This lays the foundation for future studies on the molecular mechanism of indeterminant growth and muscle repair of large fish species.

Pax3 Gene Regulated Melanin Synthesis by Tyrosinase Pathway in Pteria penguin

The paired-box 3 (Pax3) is a transcription factor and it plays an important part in melanin synthesis. In this study, a new Pax3 gene was identified from Pteria penguin (Röding, 1798) (P. penguin) by RACE-PCR (rapid-amplification of cDNA ends-polymerase chain reaction) and its effect on melanin synthesis was deliberated by RNA interference (RNAi). The cDNA of PpPax3 was 2250 bp long, containing an open reading fragment of 1365 bp encoding 455 amino acids. Amino acid alignment and phylogenetic tree showed PpPax3 shared the highest (69.2%) identity with Pax3 of Mizuhopecten yessoensis. Tissue expression profile showed that PpPax3 had the highest expression in mantle, a nacre-formation related tissue. The PpPax3 silencing significantly inhibited the expression of PpPax3, PpMitf, PpTyr and PpCdk2, genes involved in Tyr-mediated melanin synthesis, but had no effect on PpCreb2 and an increase effect on PpBcl2. Furthermore, the PpPax3 knockdown obviously decreased the tyrosinase activity, the total content of eumelanin and the proportion of PDCA (pyrrole-2,3-dicarboxylic acid) in eumelanin, consistent with influence of tyrosinase (Tyr) knockdown. These data indicated that PpPax3 played an important regulating role in melanin synthesis by Tyr pathway in P. penguin.

The DNA methylation status of MyoD and IGF-I genes are correlated with muscle growth during different developmental stages of Japanese flounder (Paralichthys olivaceus)

Many genes related to muscle growth modulate myoblast proliferation and differentiation and promote muscle hypertrophy. MyoD is a myogenic determinant that contributes to myoblast determination, and insulin-like growth factor 1 (IGF-I) interacts with MyoD to regulate muscle hypertrophy and muscle mass. In this study, we aimed to assess DNA methylation and mRNA expression patterns of MyoD and IGF-I during different developmental stages of Japanese flounder, and to examine the relationship between MyoD and IGF-I gene. DNA and RNA were extracted from muscles, and DNA methylation of MyoD and IGF-I promoter and exons was detected by bisulfite sequencing. The relative expression of MyoD and IGF-I was measured by quantitative polymerase chain reaction. IGF-I was measured by radioimmunoassay. Interestingly, the lowest expression of MyoD and IGF-I emerged at larva stage, and the mRNA expression was negatively associated with methylation. We hypothesized that many skeletal muscle were required to complete metamorphosis; thus, the expression levels of MyoD and IGF-I genes increased from larva stage and then decreased. The relative expression levels of MyoD and IGF-I exhibited similar patterns, suggesting that MyoD and IGF-I regulated muscle growth through combined effects. Changes in the concentrations of IGF-I hormone were similar to those of IGF-I gene expression. Our results the mechanism through which MyoD and IGF-I regulate muscle development and demonstrated that MyoD interacted with IGF-I to regulate muscle growth during different developmental stages.