Identification of a transforming growth factor-β type I receptor transcript in Eriocheir sinensis and its molting-related expression in muscle tissues

Cottonseed Meal Protein Hydrolysate Improves the Growth Performance of Chinese Mitten Crab (Eriocheir sinensis) by Promoting the Muscle Growth and Molting Performance

Growth retardation and prolonged marketing cycle have been noticed in the practical aquaculture of Chinese mitten crab (Eriocheir sinensis) fed with artificial feed. Plant protein hydrolysates contain a large number of small peptides and free amino acids, which can improve the growth performance of aquatic animals. However, the potential mechanisms are still not well elucidated. In this research, the influences of cottonseed meal protein hydrolysate (CPH) on the growth, feed utilization, muscle growth, and molting performance were investigated in E. sinensis. A total of 240 crabs (mean body weight 37.32 ± 0.38 g) were individually randomly distributed to six diets supplemented with 0%, 0.2%, 0.4%, 0.8%, 1.6%, and 3.2% of CPH for 12 weeks. These findings indicated that the addition of CPH at 0.4% significantly increased the survival rate, body protein gain, apparent protein utilization, trypsin and pepsin activities, and the methyl farnesoate content. When the dose reached 0.8%, the weight growth ratio, meat yield, ecdysone concentration, and the transcription of the ecdysteroid receptor all significantly increased, while the transcriptions of both myostatin and molt-inhibiting hormone significantly decreased. When CPH was added at 1.6%-3.2%, the feed conversion ratio, body crude protein content, Na+/K+-ATPase activity, and the molting ratio were all significantly improved, while the opposite was true for the transcription of the transforming growth factor-β type I receptor. The investigation results indicated that when added above 0.4%, CPH could stimulate the growth performance of E. sinensis and promote the muscle growth and molting performance.

Exploration of the regulatory mechanisms of regeneration, anti-oxidation, anti-aging and the immune response at the post-molt stage of Eriocheir sinensis

Eriocheir sinensis is widely appreciated by the surrounding population due to its culinary delicacy and rich nutrients. The E. sinensis breeding industry is very prosperous and molting is one of the important growth characteristics. Research on the regulation of molting in E. sinensis is still in the initial stages. There is currently no relevant information on the regulatory mechanisms of heart development following molting. Comparative transcriptome analysis was used to study developmental regulation mechanisms in the heart of E. sinensis at the post-molt and inter-molt stages. The results indicated that many regulatory pathways and genes involved in regeneration, anti-oxidation, anti-aging and the immune response were significantly upregulated after molting in E. sinensis. Aside from cardiac development, the differentially expressed genes (DEGs) were relevant to myocardial movement and neuronal signal transduction. DEGs were also related to the regulation of glutathione homeostasis and biological rhythms in regard to anti-oxidation and anti-aging, and to the regulation of immune cell development and the immune response. This study provides a theoretical framework for understanding the regulation of molting in E. sinensis and in other economically important crustaceans.

Toxic effects of the combined cadmium and Cry1Ab protein exposure on the protective and transcriptomic responses of Pirata subpiraticus

Cadmium (Cd) pollution poses a serious threat to agricultural production and paddy field fauna. Crystalline proteins (e.g., Cry1Ab and Cry1Ac) are secreted by Bacillus thuringiensis, which can manage pests via a complicated toxic mechanism and have been widely used for pest control due to the commercialization of transgenic crops (e.g., cotton and rice) that expresses Bt insecticidal proteins. Nonetheless, studies on the effects of combined stress of Cd and Cry1Ab protein on field indicator species are limited. In the present study, we showed that spiders, Pirata subpiraticus, fed with Cd-containing flies+Cry1Ab had dramatically higher Cd accumulation than that in the spiders fed with Cd-containing flies (p < 0.05). In addition, the enrichment of Cd led to the activation of the protective mechanism by elevating the concentrations of glutathione peroxidase, glutathione S-transferase, and metallothionein in the spiders (p < 0.05). An in-depth transcriptome analysis revealed that the activities of ion metal binding proteins, transporters, and channels might play essential roles in the Cd accumulation process. More importantly, the higher Cd concentration in the combined Cd+Cry1Ab exposure prolonged developmental duration of P. subpiraticus, due to the down-regulated cuticle proteins (CPs) encoding genes involved in the molting process, which was regulated by a series of putative transcriptional factors such as ZBTB and zf-C2H2. Collectively, this integrated analysis illustrates that the combined Cd+Cry1Ab exposure increases the adverse effects of Cd stress on the growth, antioxidase, and CPs encoding genes of P. subpiraticus, thus providing a research basis and prospect for the rationality of transgenic Cry1Ab crops in the cultivation of heavy metal contaminated soil.

A potential negative regulation of myostatin in muscle growth during the intermolt stage in Exopalaemon carinicauda

Muscle growth in crustacean is a complicated process where the muscle grows and develops through muscle restoration, and the growth rate depends on the net muscle gain during molting. Myostatin (MSTN) is a conserved inhibitor of muscle growth in vertebrates, but until now solid evidence supporting a similar function of MSTN in invertebrates has been lacking. In this study, we identified and characterized MSTN from the shrimp Exopalaemon carinicauda (EcMSTN) to better understand its biological function. The full-length cDNA of EcMSTN was 1,518 bp, encoding 428 amino acid residues, and the genomic sequence was 1,851 bp, including three exons and two introns. EcMSTN was expressed in a wide range of tissues, but predominantly detected in the abdominal muscle (P < 0.05). Low expression was detected in the cleavage, blastula and gastrula stages in the early development stages, increasing after the nauplius stage. EcMSTN expression was negatively correlated with the growth traits. After EcMSTN knockdown using RNA interference, EcMSTN expression was down-regulated in the abdominal muscle and up-regulated the expression of growth-related genes, including fast myosin heavy chain and skeletal muscle actin 3. After inhibiting EcMSTN for 5 weeks, the RNAi-treated shrimp with reduced EcMSTN levels exhibited a dramatically higher body weight compared with that of the control group. Association analysis revealed that two SNP loci g.Mstn220 and g.Mstn567 were markedly associated with both body weight and body length. The results would clarify the negative role of EcMSTN in regulating muscle growth during the intermolt stage and provide growth-related markers for molecular marker assisted breeding of E. carinicauda.

Molecular characteristic of activin receptor IIB and its functions in growth and nutrient regulation in Eriocheir sinensis

Activin receptor IIB (ActRIIB) is a serine/threonine-kinase receptor binding with transforming growth factor-β (TGF-β) superfamily ligands to participate in the regulation of muscle mass in vertebrates. However, its structure and function in crustaceans remain unknown. In this study, the ActRIIB gene in Eriocheir sinensis (Es-ActRIIB) was cloned and obtained with a 1,683 bp open reading frame, which contains the characteristic domains of TGF-β type II receptor superfamily, encoding 560 amino acids. The mRNA expression of Es-ActRIIB was the highest in hepatopancreas and the lowest in muscle at each molting stage. After injection of Es-ActRIIB double-stranded RNA during one molting cycle, the RNA interference (RNAi) group showed higher weight gain rate, higher specific growth rate, and lower hepatopancreas index compared with the control group. Meanwhile, the RNAi group displayed a significantly increased content of hydrolytic amino acid in both hepatopancreas and muscle. The RNAi group also displayed slightly higher contents of saturated fatty acid and monounsaturated fatty acid but significantly decreased levels of polyunsaturated fatty acid compared with the control group. After RNAi on Es-ActRIIB, the mRNA expressions of five ActRIIB signaling pathway genes showed that ActRI and forkhead box O (FoxO) were downregulated in hepatopancreas and muscle, but no significant expression differences were found in small mother against decapentaplegic (SMAD) 3, SMAD4 and mammalian target of rapamycin. The mRNA expression s of three lipid metabolism-related genes (carnitine palmitoyltransferase 1β (CPT1β), fatty acid synthase, and fatty acid elongation) were significantly downregulated in both hepatopancreas and muscle with the exception of CPT1β in muscles. These results indicate that ActRIIB is a functionally conservative negative regulator in growth mass, and protein and lipid metabolism could be affected by inhibiting ActRIIB signaling in crustacean.