Salinity regulates N-methylation of phosphatidylethanolamine in euryhaline crustaceans hepatopancreas and exchange of newly-formed phosphatidylcholine with hemolymph

Regulation and Response Mechanism of Acute Low-Salinity Stress during Larval Stages in Macrobrachium rosenbergii Based on Multi-Omics Analysis

Macrobrachium rosenbergii is an essential species for freshwater economic aquaculture in China, but in the larval process, their salinity requirement is high, which leads to salinity stress in the water. In order to elucidate the mechanisms regulating the response of M. rosenbergii to acute low-salinity exposure, we conducted a comprehensive study of the response of M. rosenbergii exposed to different salinities' (0‱, 6‱, and 12‱) data for 120 h. The activities of catalase, superoxide dismutase, and glutathione peroxidase were found to be significantly inhibited in the hepatopancreas and muscle following low-salinity exposure, resulting in oxidative damage and immune deficits in M. rosenbergii. Differential gene enrichment in transcriptomics indicated that low-salinity stress induced metabolic differences and immune and inflammatory dysfunction in M. rosenbergii. The differential expressions of MIH, JHEH, and EcR genes indicated the inhibition of growth, development, and molting ability of M. rosenbergii. At the proteomic level, low salinity induced metabolic differences and affected biological and cellular regulation, as well as the immune response. Tyramine, trans-1,2-Cyclohexanediol, sorbitol, acetylcholine chloride, and chloroquine were screened by metabolomics as differential metabolic markers. In addition, combined multi-omics analysis revealed that metabolite chloroquine was highly correlated with low-salt stress.

Rapid adaptive and acute stimulatory responses to low salinity stress in Pacific white shrimp (Litopenaeus vannamei): Insights from integrative transcriptomic and proteomic analysis

The Pacific white shrimp (Litopenaeus vannamei) is a euryhaline crustacean capable of tolerating a wide range of ambient salinity, but the strategies of hepatopancreas to rapid adaptive or acute stimulatory responses to extremely low salinity fluctuations remains unclear. In this study, we integrated transcriptomic and proteomic analyses on the hepatopancreas derived from rapid adaptative (RA) and acute stimulatory (AS) responses to extremely low salinity stress (0.3 ppt) to unveil specific regulatory mechanisms. The RA group displayed normal epithelial cells and tubule structures, while the AS group showed histological changes and lesions. A total of 754 and 649 differentially expressed genes (DEGs) were identified in RA and AS treatments, respectively. For proteome, a total of 206 and 66 differentially expressed proteins (DEPs) were obtained in the RA/CT and AS/CT comparison groups, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were conducted among the DEGs and DEPs, revealing that metabolic related pathways were significantly enriched pathways in both comparison groups. In addition, correlation analysis of transcriptomic and proteomic results showed that 20 and 3 pairs of DEGs/DEPs were identified in RA vs. CT and AS vs. CT comparison groups, respectively. This study is the first report on the rapid adaptive and acute stimulatory transcriptomic and proteomic responses of L. vannamei to extremely low salinity, shedding light on the mechanisms underlying osmoregulation in euryhaline crustaceans.

Dietary forage to concentrate ratios impact on yak ruminal microbiota and metabolites

To improve the rumen fermentation function and growth performance of yaks (Bos grunniens), better understanding of the effect of different dietary forage to concentrate ratios on rumen microbiota and metabolites is needed. In the present study, three diets with different dietary forage to concentrate ratios (50:50, 65:35, and 80:20) were fed to 36 housed male yaks. The changes in the distribution of rumen microorganisms and metabolites and the interactions between them were studied by 16S rRNA gene sequencing and liquid chromatography-mass spectrometry (LC–MS). The diversity and richness of microorganisms in the rumen varied according to diet. The most abundant phyla were Firmicutes and Bacteroidetes. Firmicutes was the most abundant in the C50 group, and the relative abundance of Bacteroidetes was significantly lower in the C65 group than in the C80 group (p < 0.05). The Christensenellaceae_R-7_group, Rikenellaceae_RC9_gut_group, and Methanobrevibacter had the highest relative abundances at the genus level. Among them, Christensenellace_R-7_group had the highest relative abundance in the C50 group. The Rikenellaceae_RC9_gut_group was significantly abundant in the C80 group compared with the C50 group. The Methanobrevibacter content was higher in the C65 group than in the other two groups. Both the concentration and metabolic pathways of rumen metabolites were influenced by the dietary concentrate ratio; lipids, lipid-like molecules, organic acid metabolites, and organic oxide-related metabolites differed between the groups. Significant changes were found for six metabolic pathways, including arginine and proline metabolism; glycine, serine, and threonine metabolism; glyoxylate and dicarboxylate metabolism; arginine biosynthesis; glycerophospholipid metabolism; glycerolipid metabolism; and nitrogen metabolism.

Orally administered nano-polystyrene caused vitellogenin alteration and oxidative stress in the red swamp crayfish (Procambarus clarkii)

Nanoplastics (≤100 nm) represent the smallest fraction of plastic litter and may result in the aquatic environment as degradation products of larger plastic material. To date, few studies focused on the interactions of micro- and nanoplastics with freshwater Decapoda. The red swamp crayfish (Procambarus clarkii, Girard, 1852) is an invasive species able to tolerate highly perturbed environments. As a benthic opportunistic feeder, this species may be susceptible to plastic ingestion. In this study, adult P. clarkii, at intermolt stage, were exposed to 100 μg of 100 nm carboxylated polystyrene nanoparticles (PS NPs) through diet in a 72 h acute toxicity test. An integrated approach was conceived to assess the biological effects of PS NPs, by analyzing both transcriptomic and physiological responses. Total hemocyte counts, basal and total phenoloxidase activities, glycemia and total protein concentration were investigated in crayfish hemolymph at 0 h, 24 h, 48 h and 72 h from PS NPs administration to evaluate general stress response over time. Differentially expressed genes (DEGs) in the hemocytes and hepatopancreas were analyzed to ascertain the response of crayfish to PS NP challenge after 72 h. At a physiological level, crayfish were able to compensate for the induced stress, not exceeding generic stress thresholds. The RNA-Sequencing analysis revealed the altered expression of few genes involved in immune response, oxidative stress, gene transcription and translation, protein degradation, lipid metabolism, oxygen demand, and reproduction after PS NPs exposure. This study suggests that a low concentration of PS NPs may induce mild stress in crayfish, and sheds light on molecular pathways possibly involved in nanoplastic toxicity.

Growth, Metabolite, Antioxidative Capacity, Transcriptome, and the Metabolome Response to Dietary Choline Chloride in Pacific White Shrimp Litopenaeus vannamei

Simple Summary

Choline is a vitamin-like nutrient and has many metabolic and physiological functions in aquatic animals. Unfortunately, the information on the optimal requirement of dietary choline in Litopenaeus vannamei is limited, and the molecular and metabolic mechanisms of choline on L. vannamei are unclear. Hence, in this study, the growth performance, whole-body composition, serum characteristics, hepatopancreatic antioxidant indexes, serum metabolome and hepatopancreas transcriptome were performed. In this study, the growth of L. vannamei was not affected by dietary choline. Dietary choline played an important role in arachidonic acid and glycerophospholipid metabolism and decreased the oxidant damage of L. vannamei, while excessive choline can inhibit the digestion of protein and reduce the whole-body crude protein in shrimp. Based on the results of weight gain and lipid peroxidation reduction, 1082 mg/kg dietary choline could meet the growth requirement of L. vannamei, but 2822 mg/kg dietary choline was needed to reduce peroxidation damage. The present study would provide valuable information on the requirement of choline in L. vannamei, and help to understand the molecular and metabolic mechanisms of choline in shrimp.

Abstract

To determine the response of Pacific white shrimp Litopenaeus vannamei to different levels of dietary choline, juvenile white shrimp (1.75 ± 0.09 g) were fed six semi-purified diets supplemented with 0 (control), 2000, 4000, 6000, 8000, and 12,000 mg/kg choline chloride for eight weeks. Growth performance, whole-body composition, serum characteristics and hepatopancreatic antioxidant indexes were evaluated. Meanwhile, serum metabolome and hepatopancreas transcriptome were performed to examine the overall difference in metabolite and gene expression. The weight gain, survival, specific growth rate, condition factor and hepatosomatic index were not affected by dietary choline levels. The shrimp fed 6000 mg/kg dietary choline chloride gained the maximal whole-body crude protein, which was significantly higher than that of shrimp fed with 12,000 mg/kg dietary choline. Serum total cholesterol of shrimp fed 6000 mg/kg dietary choline was higher than that in shrimp fed 4000 mg/kg choline. Dietary choline significantly decreased malondialdehyde content, superoxide dismutase, and glutathione peroxidase activities in shrimp hepatopancreas. Compared with the shrimp fed 6000 mg/kg dietary choline chloride, the glycerophospholipid metabolism pathway was significantly enriched in the shrimp fed 0 mg/kg dietary choline chloride, and the choline content and bile salt-activated lipase-like expression were upregulated. The expression of trypsin-1-like in protein digestion and absorption pathway was significantly downregulated in the shrimp fed 12,000 mg/kg dietary choline chloride. Apolipoprotein D might be a potential biomarker in shrimp, and dietary choline played an important role in lipid metabolism, especially in the reduction of oxidative damage in L. vannamei. Based on the results of weight gain and degree of oxidative damage, 1082 mg/kg dietary choline could meet the growth requirement of L. vannamei, but 2822 mg/kg dietary choline was needed to reduce peroxidation damage.

Growth and Lipidomic Responses of Juvenile Pacific White Shrimp Litopenaeus vannamei to Low Salinity

The Pacific white shrimp (Litopenaeus vannamei), a euryhaline penaeid species, can tolerate a wide range of salinities, but little is known on its strategies to cope with low salinity fluctuations from the aspect of lipidomics. Thus, in this study, L. vannamei were grown in two different salinities [3 and 30‰ (control)] for 8 weeks, and then an liquid chromatography (LC)-mass spectrometry (MS)-based lipidomics analysis was performed to reveal the lipid profile differences in gill and muscle. L. vannamei under low salinity had lower weight gain and condition factor than the control shrimp at 30‰, but no differences were found in survival and hepatopancreas index. A higher number of differential lipid metabolites were identified in gill than in muscle in L. vannamei at salinity 3‰ relative to the control shrimp at salinity of 30‰ (159 versus 37), which belonged to 11 and 6 lipids classes, respectively. Of these lipids, phosphatidylcholine (PC), phosphatidylinositol (PI), phosphatidic acid (PA), phosphatidylethanolamine (PE), and triglyceride (TG) were the main lipids in both shrimp gill and muscle, regardless of salinities. Compared with the control shrimp at salinity 30‰, the percentage of PC significantly reduced, but TG and PA significantly increased in gill of shrimp at salinity 3‰. Moreover, the relative fatty acid abundances showed significant changes in L. vannamei between the two salinity groups, but the patterns of the changes were complex and were fatty acid dependent. Neither lipid nor fatty acid composition in muscle was affected by salinity. Further pathway analysis showed that these metabolites were closely related to lipid and fatty acid metabolic pathways. All the findings in this study reveal that the lipid variations are closely related to bio-membrane structure, mitochondrial function, energy supply, or organic osmolyte contents in hemolymph for improving osmoregulatory capacity of L. vannamei under low salinity.

Disentangling structural genomic and behavioural barriers in a sea of connectivity

Genetic divergence among populations arises through natural selection or drift and is counteracted by connectivity and gene flow. In sympatric populations, isolating mechanisms are thus needed to limit the homogenizing effects of gene flow to allow for adaptation and speciation. Chromosomal inversions act as an important mechanism maintaining isolating barriers, yet their role in sympatric populations and divergence with gene flow is not entirely understood. Here, we revisit the question of whether inversions play a role in the divergence of connected populations of the marine fish Atlantic cod (Gadus morhua), by exploring a unique data set combining whole‐genome sequencing data and behavioural data obtained with acoustic telemetry. Within a confined fjord environment, we find three genetically differentiated Atlantic cod types belonging to the oceanic North Sea population, the western Baltic population and a local fjord‐type cod. Continuous behavioural tracking over 4 year revealed temporally stable sympatry of these types within the fjord. Despite overall weak genetic differentiation consistent with high levels of gene flow, we detected significant frequency shifts of three previously identified inversions, indicating an adaptive barrier to gene flow. In addition, behavioural data indicated that North Sea cod and individuals homozygous for the LG12 inversion had lower fitness in the fjord environment. However, North Sea and fjord‐type cod also occupy different depths, possibly contributing to prezygotic reproductive isolation and representing a behavioural barrier to gene flow. Our results provide the first insights into a complex interplay of genomic and behavioural isolating barriers in Atlantic cod and establish a new model system towards an understanding of the role of genomic structural variants in adaptation and diversification.

Small organic solutes in sticky droplets from orb webs of the spider Zygiella atrica (Araneae; Araneidae): β-alaninamide is a novel and abundant component

In northeastern North America, Zygiella atrica often build their orb webs near the ocean. We analyzed individual field-built Z. atrica webs to determine if organic low-molecular-mass solutes (LMM) in their sticky droplets showed any unusual features not previously seen in orb webs of other species living in less salty environments. While two of the three most abundant organic LMM (putrescine (butane-1,4-diamine) and GABamide (4-aminobutanamide)) are already well-known from webs of inland spiders, the third major LMM, β-alaninamide (3-aminopropanamide), a homolog of GABamide, has not been detected in sticky droplets from any other araneoid spiders (27 species). It remains to be established, however, whether or not use of β-alaninamide is related to proximity to saltwater. We observed variability in organic LMM composition in Z. atrica webs that appeared to be influenced more by an undetermined factor associated with different collecting locations and/or collection dates than by different genders or instars. Shifts in composition when adult females were transferred from the field to the laboratory were also observed. Structural similarities and inverse correlations among β-alaninamide, GABamide, and N-acetylputrescine suggest that they may form a series of LMM fulfilling essentially the same, as yet unknown, role in the webs of those species in which they occur.

Synthesis of phosphatidylcholine through phosphatidylethanolamine N-methylation in tissues of the mussel Mytilus galloprovincialis

We previously demonstrated the importance of upregulation of phosphatidylethanolamine N-methylation pathway in euryhaline fish and crustaceans facing hyperosmotic conditions. In marine molluscs phosphatidylcholine synthesis through N-methylation of phosphatidylethanolamine has not been described until now. In vivo labeling of the mussel Mytilus galloprovincialis with [1-(3)H]-ethanolamine showed that the digestive gland is the tissue expressing the highest incorporation into lipids. A sustained increase in lipid labeling was observed up to 72 h following label injection with 79-92% of radioactivity concentrated into phosphatidylethanolamine and phosphatidylcholine. A direct correlation (r = 0.47, p < 0.01) between the specific radioactivities of phosphatidylcholine in plasma and the digestive gland was observed. Moreover, the phosphatidylcholine fatty acid compositions of plasma and the digestive gland were similar but differed from those of phosphatidylcholine purified from other tissues. In vitro incubation of tissues with [1-(3)H]-ethanolamine or L-[3-(3)H]-serine showed that a significant labeling of the choline moiety of phosphatidylcholine was observed in the digestive gland and hemocytes. Pulse-chase experiments with [1-(3)H]-ethanolamine also demonstrated that hemocytes are exchanging the newly formed phospholipids with plasma. Finally, phosphatidylethanolamine N-methyltransferase assays demonstrated salinity-dependent activities in the digestive gland and hemocytes. We conclude that in M. galloprovincialis an active phosphatidylcholine synthesis through N-methylation of phosphatidylethanolamine occurs in the digestive gland and hemocytes and that this newly formed phosphatidylcholine is partly exchanged with plasma.