Comparative cation dependency of sugar transport by crustacean hepatopancreas and intestine

Hepatopancreas immune response during different photoperiods in the Chinese mitten crab, Eriocheir sinensis

Photoperiod plays an important role in the growth, development, and metabolism of crustaceans. The growth and reproduction of crabs are closely related to the photoperiod. The hepatopancreas is an important source of innate immune molecules; however, hepatopancreatic patterns of gene expression depending on the photoperiod-which may underlie changes in immune mechanisms-remain unknown. To study the molecular basis of immune regulation in the Chinese mitten crab (Eriocheir sinensis) under different light conditions, a new generation of high-throughput Illumina sequencing technology was used, and functional genes associated with immune function in the hepatopancreas of this crab were explored via assembly of high-quality sequences, gene annotation, and classification. A total of 383,899,798 clean reads from the hepatopancreas of the normal group (12 h/12 h L:D), 387,936,676 clean reads from the continuous light group (24 h/0 h L:D), and 384,872,734 clean reads from the continuous darkness group (0 h/24 h L:D) were obtained. Compared with the normal group, 141, 152, 60, 87, 90, and 101 differentially expressed genes were identified in the groups exposed to continuous light for 2 days, continuous darkness for 2 days, continuous light for 4 days, continuous darkness for 4 days, continuous light for 6 days, and continuous darkness for 6 days, respectively. The results of this study revealed that under continuous light and dark conditions, the crabs were most affected by light on day 2, but the interference gradually decreased with time. We suggest that long-term light or dark treatment makes crabs adaptable to fluctuations in the photoperiod. The expression of genes associated with immune response patterns was found to change during different photoperiods. Prophenoloxidase (proPO) and serine proteinase (kazal-type serine proteinase inhibitor 1 and serine proteinase inhibitor-3) in the proPO-activating system were significantly upregulated in the 2-day continuous light group. Glutathione peroxidase 3 was significantly downregulated under continuous light exposure, while cyclooxygenase was upregulated in the continuous light and dark environments. These results provide insights into the molecular mechanism underlying the effects of the photoperiod on immune regulation and the physiological activity of E. sinensis.

Synthesis of digestive enzymes, food processing, and nutrient absorption in decapod crustaceans: a comparison to the mammalian model of digestion

The ∼15.000 decapod crustaceans that are mostly omnivorous have evolved a structurally and functionally complex digestive system. They have highly effective cuticular chewing and filtering structures in the stomach, which are regularly renewed by moulting. Decapods produce a broad range of digestive enzymes including chitinases, cellulases, and collagenases with unique properties. These enzymes are synthesized in the F-cells of the hepatopancreas and are encoded in the genome as pre-pro-proteins. In contrast to mammals, they are stored in a mature form in the lumen of the stomach to await the next meal, and therefore, the enzymes are particularly stable. The fat emulsifiers are fatty acyl-dipeptides rather than bile salts. After mechanical and chemical processing of the food in the cardiac stomach, the chyme is filtered by two unique filter systems of different mesh-size. The filtrate is then transferred to the hepatopancreas where the nutrients are absorbed by the R-cells, mostly via carriers, resembling nutrient absorption in the small intestine of mammals. The absorbed nutrients are used to fuel the metabolism of the hepatopancreas, are supplied to other organs, and are stored in the R-cells as glycogen and lipid reserves. Export lipids are secreted from the R-cells into the haemolymph as high density lipoproteins that mainly consist of phospholipids. In contrast to mammals, the midgut tube and hindgut contribute only little to food processing and nutrient absorption. The oesophagus, stomach and hindgut are well innervated but the hepatopancreas lacks nerves. Hormone cells are abundant in the midgut and hepatopancreas epithelia. Microorganisms are often present in the intestine of decapods, but they are apparently not essential for digestion and nutrition.

Two sodium pumps in the hepatopancreas of the intertidal euryhaline crab Neohelice granulata: biochemical characteristics and differential modulation after feeding

No study has been done on the existence, biochemical characteristics, and modulation of K+-independent ouabain-insensitive Na+ ATPase activity (the second sodium pump) in the digestive tract of intertidal euryhaline crabs and moreover on the coexistence and modulation under distinct physiological and (or) environmental conditions of different sodium pumps. We determined the occurrence, characteristics, and responses at different times (0, 1, 24, 48, and 120 h) after feeding upon distinct salinities of Na+ ATPase activity and Na+/K+ ATPase in the hepatopancreas of Neohelice granulata (Dana, 1851), which is a model species. The stimulation by Na+ under total inhibition of Na+/K+ ATPase activity revealed the occurrence of Na+ ATPase activity that was totally inhibited by 2 mmol·L–1 furosemide, exhibits Michaelis–Menten kinetics for ATP (apparent Km = 0.52 ± 0.16 mmol·L–1), and highest activity at around pH 7.4. In crabs acclimated to 35 psu (osmoconforming conditions), Na+ ATPase activity was highly increased (about 15-fold) (532 ± 58 nmol Pi·mg protein−1·min−1) in the hepatopancreas 48 h after feeding. In 10 psu (hyper-regulating conditions), Na+ ATPase activity decreased in the hepatopancreas 24 h after feeding (7 ± 9 nmol Pi·mg protein−1·min−1) and recovered initial values after 48 h (24 ± 35 nmol Pi·mg protein−1·min−1). Unlike Na+ ATPase, Na+/K+ ATPase activity did not change after feeding at any salinity, suggesting the specific modulation of the second sodium pump and its role in postprandial adjustments in the hepatopancreas.

Functional characterization of a novel disaccharide transporter in lobster hepatopancreas

In animals, the accepted model of carbohydrate digestion and absorption involves reduction of disaccharides into the monosaccharides glucose, fructose, and galactose followed by their individual transmembrane transport into cells. In 2011, a gene for a distinct disaccharide sucrose transporter (SCRT) was found in Drosophila melanogaster and characterized in a yeast expression system. The purpose of the present investigation was to functionally identify and characterize a putative disaccharide transporter analog in the hepatopancreas of the American lobster, Homarus americanus. Purified hepatopancreatic brush-border membrane vesicles (BBMV) were used in transport experiments using ¹⁴C-sucrose and a Millipore filter isolation technique. In the absence of sodium, an external pH of 4 significantly stimulated the uptake of ¹⁴C-sucrose compared to that occurring at pH 5, 6, or 7. At pH 7, increasing external concentrations of sodium increased ¹⁴C-sucrose uptake by BBMV in a hyperbolic fashion and this stimulation was significantly reduced when the pH was changed to 4, suggesting that both protons and sodium ions were each capable of driving the uptake of the sugar. In experiments with a variety of monosaccharides, disaccharides, and trisaccharides, used as potential inhibitors of ¹⁴C-sucrose uptake, only maltose and trehalose inhibited carrier-mediated ¹⁴C-sucrose transport. An additional experiment showed that 20 mM maltose was a competitive inhibitor of ¹⁴C-sucrose uptake. The use of a putative lobster SCRT by both maltose and trehalose is nutritionally appropriate for lobsters as they commonly digest glycogen and chitin, polymers of maltose and trehalose, respectively. These findings suggest there is a brush-border proton- or sodium-dependent, hepatopancreatic carrier process, shared by sucrose, maltose, and trehalose, that may function to absorb disaccharides that are produced from digestion of naturally occurring dietary constituents.