Formation of phospholipid nitrogenous bases in euryhaline fish and crustaceans. I. Effects of salinity and temperature on synthesis of phosphatidylserine and its decarboxylation

Using a metabolomics approach to investigate the sensitivity of a potential Arctic-invader and its Arctic sister-species to marine heatwaves and traditional harvesting disturbances

Coastal species are threatened by fishing practices and changing environmental conditions, such as marine heatwaves (MHW). The mechanisms that confer tolerance to such stressors in marine invertebrates are poorly understood. However, differences in tolerance among different species may be attributed to their geographical distribution. To test the tolerance of species occupying different thermal ranges, we used two closely related bivalves the softshell clam Mya arenaria (Linnaeus, 1758), a cold-temperate invader with demonstrated potential for establishment in the Arctic, and the blunt gaper Mya truncata (Linnaeus, 1758), a native polar species. Clams were subjected to a thermal stress, mimicking a MHW, and harvesting stress in a controlled environment. Seven acute temperature changes (2, 7, 12, 17, 22, 27, and 32 °C) were tested at two harvesting disturbance intensities (with, without). Survival was measured after 12 days and three tissues (gills, mantle, and posterior adductor muscle) collected from surviving individuals for targeted metabolomic profiling. MHW tolerance differed significantly between species: 26.9 °C for M. arenaria and 17.8 °C for M. truncata, with a negligeable effect of harvesting. At the upper thermal limit, M. arenaria displayed a more profound metabolomic remodelling when compared to M. truncata, and this varied greatly between tissue types. Network analysis revealed differences in pathway utilization at the upper MHW limit, with M. arenaria displaying a greater reliance on multiple DNA repair and expression and cell signalling pathways, while M. truncata was limited to fewer pathways. This suggests that M. truncata is ill equipped to cope with warming environments. MHW patterning in the Northwest Atlantic may be a strong predictor of population survival and future range shifts in these two clam species. As polar environments undergo faster rates of warming compared to the global average, M. truncata may be outcompeted by M. arenaria expanding into its native range.

Effects of different temperatures on seawater acclimation in rainbow trout Oncorhynchus mykiss: osmoregulation and branchial phospholipid fatty acid composition

This study aimed to investigate the effects of different temperatures on seawater acclimation in rainbow trout (Oncorhynchus mykiss), in terms of growth performance, osmoregulatory capacity, and branchial phospholipid fatty acid (PLFA) composition. The fish (initial weight, 94.73 g) were reared at 9, 12.5, and 16 °C for 28 days, then acclimated to seawater, and subsequently reared for 14 days. Sampling points were on the last day in freshwater, and the 1st, 4th, 7th, and 14th days after the salinity reached 30. The results showed the final weight, percent weight gain, and specific growth rate of rainbow trout at 12.5 °C were significantly higher than those at 9 °C, while the thermal growth coefficient at 16 °C was significantly lower than that in other treatments. The branchial PLFA composition in rainbow trout changed more rapidly at 9 and 12.5 °C than at 16 °C. The branchial PLFA composition was significantly affected by temperature and salinity and their interaction. The polyunsaturated fatty acid content of phospholipids in the gill at 9 and 12.5 °C was significantly higher than those at 16 °C. Low temperature (9 °C) and seawater acclimation significantly increased the degree of unsaturation of membrane, enhancing membrane fluidity, which is related to Na⁺-K⁺ ATPase activity. Responses of plasma ion, Na⁺-K⁺ ATPase activity, and plasma glucose followed a similar pattern at different temperatures. Overall, the study suggests that 12.5 °C is the ideal temperature for seawater acclimation in rainbow trout.

Effects of seawater acclimation at constant and diel cyclic temperatures on growth, osmoregulation and branchial phospholipid fatty acid composition in rainbow trout Oncorhynchus mykiss

The study investigated the effects of seawater acclimation at constant and diel temperatures on the growth, osmoregulation, and branchial phospholipid fatty acid (PLFA) composition in rainbow trout (Oncorhynchus mykiss). The fish (initial weight, 62.28 ± 0.41 g) were reared at a constant 13.0 °C (CT) or with a diel cycle of either 13.0 ± 1.0 °C (VT2) or 13.0 ± 2.0 °C (VT4) for 6 weeks, and subsequently subjected to seawater acclimation. Diel temperature variations (of up to 4 °C) did not affect the growth rate of rainbow trout maintained in freshwater, but alleviated the impairment on the growth after seawater challenge. Under all temperature conditions, rainbow trout were well prepared to seawater acclimation. The diel cyclic temperature resulted in fish with reduced fluctuations in plasma electrolyte levels, branchial Na⁺-K⁺ ATPase activity, and plasma osmolality. In freshwater, the sum of the monounsaturated fatty acids was significantly higher in the VT4 relative to CT and VT2 treatment. Conversely, the sum of polyunsaturated fatty acids was significantly lower in the VT4 fish. After seawater transfer, the branchial PLFA profiles of the fish significantly changed, but those in CT and VT2 did not recover afterwards (the degree of unsaturation was downregulated). The PLFA composition of fish in the VT4 treatment appeared to be steadier under seawater acclimation. This study suggests that a diel cyclic temperature (13.0 ± 2.0 °C) can alleviate the impairment of growth, enhance osmoregulation capability, and improve the stability of the branchial PLFA composition in rainbow trout after seawater acclimation.

Effect of seasonal and experimental temperature on de novo synthesis of fatty acids in C. crangon

The intensity of in vivo lipogensis was measured and in this purpose, the radioactivity of incorporation of tritium into fatty acids (FAs) in tissues of C. crangon was determined. De novo synthesis of FAs was five times higher in hepatopancreas than in muscle in summer period but not much higher in autumn. The higher FAs synthesis was recorded at 25 °C, both for hepatopancreas and muscle, and the summer was higher than the autumn in the hepatopancreas and in the muscles of the opposite situation was observed. The higher amounts of SFAs in hepatopancreas from autumn, when in experimental conditions the ambient temperature C. crangon changed from 6 °C to the experimental higher temperature. When content of PUFAn-3 declined dramatically (Autumn 1 h, 25 °C). In contrast, at a lower temperature, the amount of polyunsaturated FAs is much higher than at 25 °C (Autumn 1 h 6 °C).

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.

Conservation of the PRM1→PRM2→TNP2 Domain

In mouse and human, the genes encoding protamines PRM1, PRM2 and transition protein TNP2 are found clustered together on chromosome 16. In addition, these three genes lie in the same orientation to one another and are coordinately expressed in a haploid-specific manner during spermatogenesis. Previously, we have shown that the human PRM1 --> PRM2 --> TNP2 locus exists as a single chromatin domain bounded by two male germ cell-specific MARs, i.e. Matrix Attachment Regions. A third, somatic-specific MAR element lies immediately 3' of the PRM1 --> PRM2 --> TNP2 domain. This MAR maps to a conserved CpG island 5' of the human SOCS-1 gene. Similarly, two candidate MARs flank the mouse Prm1 --> Prm2 --> Tnp2 domain. Comparative analysis of the mouse and human promoter regions identified several conserved regulatory motifs for each of the genes of this cluster. This further establishes the synteny of this region. Global structural similarities and the functional relevance of the associated candidate regulatory elements are discussed.

The responses of rainbow trout gills to high lithium and potassium concentrations in water

The objective of this study is to discern the effects of increased waterborne lithium and potassium on rainbow trout gill histology, lipid composition, and enzyme activity. The study aims to elucidate the effects of these ions in the laboratory in concentrations similar to those prevailing in a forest lake Poppalijärvi in a contaminated mining area in NW Russia. Under the lithium and potassium exposure, the fish were further stressed by high pH (8.2 as in Lake Poppalijärvi) and lack of food. These multiple stress conditions altered the gill membrane fluidity by increasing sphingomyelin (5.5+/-0.6 compared to 2.9+/-0.3% in the control) and reducing cholesterol (4+/-1 compared to 17+/-3 mg g(-1) in the control). The total ATPase activity tended to be higher in the lithium-potassium-exposed group (46+/-6 compared to 34+/-2 micromol Pi h(-1) mg(-1)protein in the control). Lithium toxicity was lowered here by the protective role of higher potassium contents.

Lipids as energy source during salinity acclimation in the euryhaline crab Chasmagnathus granulata dana, 1851 (crustacea-grapsidae)

Lipids seem to be the major energy store in crustaceans. Moreover, they are extremely important in maintaining structural and physiological integrity of cellular and sub cellular membranes. During salinity adaptation, energy-demanding mechanisms for hemolymph osmotic and ionic regulation are activated. Thus, the main goal of this work was to verify the possible involvement of lipids as an energy source in the osmotic adaptation process. The estuarine crab Chasmagnathus granulata was captured and acclimated to salt water at 20 per thousand salinity and 20 +/- 2 degrees C, for 30 days. After acclimation, crabs were divided into groups of ten and transferred to fresh water (0 per thousand ), salt water at 40 per thousand salinity, or maintained in salt water at 20 per thousand salinity (control group), without feeding. Before and seven days after the salinity change, wet weight and lipid concentration in gills, muscle, hepatopancreas, and hemolymph were determined according to the colorimetric assay of sulphophosphovanilin. Results show that hepatopancreas lipids were not mobilized during osmotic stress regulation. Gill and muscle lipids were significantly lower in crabs subjected to hypo-osmotic stress than those subjected to the hyper-osmotic stress or maintained at the control salinity. Our results point to the occurrence of lipid mobilization and involvement of these compounds in the osmotic acclimation process in C. granulata, but with differences between tissues and the osmotic shock (hypo or hyper) considered.

Changes in the fatty acid composition of phospholipids in tissues of farmed sea bass (Dicentrarchus labrax) during an annual cycle. Roles of environmental temperature and salinity

We quantified seasonal effects on fatty acid composition of tissue phospholipids in farmed sea bass. Major changes in percent phosphatidylethanolamine and phosphatidylcholine were observed in all tissues between February and March, and the phosphatidylcholine/phosphatidylethanolamine ratio was drastically reduced at this time. Different changes in the fatty acid composition of total phospholipids were observed in all tissues examined. Fish fed all year on the same commercial diet showed a significant correlation between water salinity and percentage of 22:6n-3 in muscle, liver and gill phospholipids, but no correlation was found between percent 22:6n-3 of phospholipids and water temperature. In each tissue, we observed annual variation in the 20:5n-3/20:4n-6 ratio in phospholipids, but maximum and minimum values occurred at different times in each organ. From these results, we conclude that salinity can play a significant role in modulating the activities of enzymes acting on lipid metabolism during their natural circannual cycles.