Comparative Biochemistry and Physiology B-Biochemistry & Molecular Biology最新文献

Calcifying organisms are suffering from negative impacts induced by climate change, such as CO₂-induced acidification, which may impair external calcified structures. Freshwater mollusks have the potential to suffer more from CO₂-induced acidification than marine calcifiers due to the lower buffering capacity of many freshwater systems. One of the most important enzymes contributing to the biomineralization reaction is carbonic anhydrase (CA), which catalyzes the reversible conversion of CO₂ to bicarbonate, the major carbon source of the calcareous structure in calcifiers. In this study we characterized two α-CA isoforms (LsCA1 and LsCA4) from the freshwater snail Lymnaea stagnalis using a combination of gene sequencing, gene expression, phylogenetic analysis and biochemical assays. Both CA isoforms demonstrated high expression levels in the mantle tissue, the major site for biomineralization. Furthermore, expression of LsCA4 during development parallels shell formation. The primary protein structure analysis, active site configuration and the catalytic activity of LsCA4 together suggest that the LsCA4 is embedded in the apical and basolateral membranes of mantle cells; while LsCA1 is proposed to be cytosolic and might play an important role in acid-base regulation. These findings of LsCA isoforms form a strong basis for a more detailed physiological understanding of the effects of elevated CO₂ on calcification in freshwater mollusks.

The hake fishery plays a crucial role due to its significant economic impact. The genus Merluccius includes 12 extant species found along the coasts of the Americas, Europe, and Africa. However, research on their digestive physiology and the enzymes involved in digestion, including proteases, remains limited. Proteases play a key role in protein digestion, a vital process for all living organisms. This study focused on screening the genomes of eight Merluccius spp. for eight specific proteases previously identified in Merluccius polli. Additionally, the study conducted biochemical analyses of proteases found in the stomach and intestine of Pacific whiting fish (Merluccius productus), comparing the results with the genomic findings. The analysis revealed that proteases across Merluccius spp. are conserved, although with slight variations, particularly in chymotrypsin and aspartic proteases. Biochemical characterization of M. productus identified at least three main proteases in the stomach, active at acidic pH, and at least seven proteases in the intestine, active at alkaline pH, as determined by electrophoresis. Further investigation, including specific inhibition studies, determination of molecular mass, and assessment of pH and temperature preferences for catalysis, revealed that one of the stomach proteases functioning at acidic pH likely belongs to the acid peptidase class, likely pepsin. Similarly, analysis of proteases active at alkaline pH indicated the presence of a chymotrypsin and a trypsin, consistent with genomic findings in M. productus. These results are important as they provide insights into the digestive physiology of Merluccius spp., contributing to a better understanding of their nutritional needs.

Mitochondria play a critical role in follicular development and ovulation, at least in part through the actions of growth hormone (GH)/insulin-like growth factor-1 (IGF-1) on mitochondrial biogenesis. This study aimed to identify seasonal alterations in the GH/IGF-1 system and mitochondrial biogenesis in muskrat (Ondatra zibethicus) ovaries. We utilized the muskrat, a typical seasonal breeder, to clarify the potential impact of the GH/IGF-1 system on mitochondrial biogenesis across different breeding seasons using immunohistochemistry, gene expression and high-throughput sequencing. Alterations in follicular development existed in muskrat ovaries between the breeding season (BS) and non-breeding season (NBS), accompanied by a striking decrease in circulating and ovarian GH and IGF-1 concentrations. GH, GHR, IGF-1, IGF-1R, and mitochondrial biogenesis markers were localized in the ovarian cells of muskrats during both seasons. In contrast, Gh, Ghr, Igf-1, Igf-1r, Ppargc1a, Ppargc1b, Tfam, and Nrf1/2 mRNA levels were higher in BS. The relative levels of GH and IGF-1 in circulation and ovaries were positively associated with mitochondrial biogenesis markers. Additionally, RNA-seq analysis demonstrated that differentially expressed genes might be associated with insulin and PI3K/Akt signaling pathways, as well as mitochondrial function-related pathways. These findings suggest that the intra-ovarian GH/IGF-1 system, which is associated with seasonal changes in mitochondrial biogenesis, is activated in muskrat ovaries in BS.

Water temperature is an abiotic factor influencing fish metabolism and physiological responses. As poikilothermic creatures, fish are notable sensitivity to fluctuations in water temperature, which also significantly influences intestinal microbial proliferation. This study aimed to investigate the impact of both low (8 °C) and high (28 °C) water temperatures on oxidative stress and the intestinal microbiota of Chromis notata, a species that has recently migrated northward owing to changes in sea water temperature. Laboratory experiments were conducted to assess changes in superoxide dismutase (SOD), catalase (CAT), and lysozyme activities, as well as changes in the abundance and diversity of intestinal microbiota. The activities of antioxidant enzymes, specifically SOD and CAT, in C. notata exposed to low and high temperatures, showed an increase compared to the control group (maintained at 18 °C). Moreover, liver H₂O₂ levels exhibited a significant increase over time. Conversely, plasma lysozyme activity significantly decreased in groups subjected to low and high water temperatures compared to the control group. Analyzing changes in the intestinal microbiota, we observed an increase in the proportion of Firmicutes but a decrease in Proteobacteria, which are known for their role in immune enhancement, in C. notata exposed to both low and high water temperatures. We propose that alterations in water temperature impact the antioxidant enzyme activity of C. notata, leading to compromised immune responses and disruption of the biological balance of the intestinal microbiota, potentially affecting the host's survival.

Plumage ornaments act as important sexual signals, though the extent to which these ornaments act as honest signals—and the physiological mechanisms that maintain honesty—remain poorly understood. We studied the pigmentary basis of tail color in the American Redstart (Setophaga ruticilla), a species of songbird with sexual dichromatism and delayed plumage maturation; younger males resemble females, only replacing their yellow feathers for bright orange ones after the first breeding season. The yellow rectrices of females and young males and the orange feathers of older males largely contain the same pigments, but in vastly different proportions. Whereas the feathers of females and young males contain primarily lutein, 3′-dehydro-lutein and canary-xanthophylls, those of older males contain primarily 4-keto-carotenoids. The presence of lutein and the predominance of α-doradexanthin as 4-keto-carotenoid, a pigment with a shortened chain of conjugated double bonds compared to keto-carotenoids commonly found in red feathers, in the feathers of older males contribute to their uncommon orange hue. Since the orange coloration of the tail in the American redstart results from the combination of yellow, orange, and red pigments, this is a system where slight adjustments in the types of carotenoids deposited could significantly alter hue. Factors either work against achieving the most oxidized state in this species or the hue is maintained through stabilizing selection for a favored color. The color metrics of Carotenoid Chroma, Visible Hue, λ_R50 and tetrahedral θ best captured differences in pigment concentration and make-up, and are recommended in future spectrophotometric studies of carotenoid-based traits.

To identify daily changes in the digestive physiology of Totoaba macdonaldi, the feed intake, activity (pepsin, trypsin, chymotrypsin, lipase, amylase, and L-aminopeptidase), and gene expression (aminopeptidase and maltase-glucoamylase) of key digestive enzymes were measured in the intestine and the pyloric caeca. Fish were fed for three weeks every four hours during the light period to apparent satiation, and samples were taken every four hours throughout a 24-h cycle under a 12:12 L:D photoperiod. The feed consumption steadily increased until the third feeding (16:00 h, ZT-8) and decreased significantly towards the end of the day. The activity of pepsin and alkaline enzymes (trypsin, chymotrypsin, lipase, amylase, and L-aminopeptidase) exhibited a pattern dependent on the presence of feed, showing a significant reduction during the hours of darkness (ZT-12 to ZT-24). Expression of the intestinal brush border enzyme (L-aminopeptidase) increased during the darkness period in anticipation of the feed ingestion associated with the subsequent light period. The cosinor analysis used to estimate the feed rhythms for all tested enzymes showed that activity in the intestine and pyloric caeca exhibited significant rhythmicity (p < 0.05). However, no rhythmicity was observed in the intestinal expression of maltase-glucoamylase. Our results demonstrate that some of the behavioral and digestive physiology features of totoaba directly respond to rhythmicity in feeding, a finding that should be considered when establishing optimized feeding protocols.

The polyunsaturated fatty acid docosahexaenoic acid (DHA) significantly influences fish growth and lipid metabolism. Nevertheless, the specific mechanism by which DHA is transported and exerts its effects remains unclear. Scavenger receptor class B type I (SCARB1) is essential for maintaining cellular cholesterol levels and regulating the immune system in mammals, as well as facilitating the uptake of fatty acids (FAs). Another class B scavenger receptor, cluster-determinant 36 (CD36), is involved in promoting the uptake and transport of long-chain fatty acids. However, the molecular characteristics of the grass carp scarb1 gene have not yet been reported, and the potential role of Scarb1 and Cd36 in mediating DHA transport and metabolism remains uncertain. This study aimed to investigate the effects of Scarb1 and Cd36 on DHA transport. Initially, grass carp scarb1–1 and scarb1–2 were cloned. Predictions were made regarding their structural characteristics, including number and presence of transmembrane domains and glycosylation sites. Furthermore, gene structure analysis revealed that scarb1–1 has two additional exons in the 3′-region compared to scarb1–2. The multiple sequence alignment indicated that Scarb1 exhibits conserved motifs and amino acid residues across vertebrates. mRNA expression of scarb1–1 was the highest in the intestine, while scarb1–2 was highest expressed in adipose tissue, with both having lower expression levels in muscle tissue. Scarb1–1 was primarily localized on the cell membrane, whereas Scarb1–2 was found in both the cell membrane and cytoplasm. After overexpression of grass carp Scarb1–1, Scarb1–2, and Cd36 in HEK 293 T cells, DHA incubation showed that only Cd36 significantly increased cellular DHA relative content, suggesting a potential role of Cd36 in DHA transport. These findings will serve as a basis for further research on fatty acid transport in fish.

A critical role of omega-3 polyunsaturated fatty acids (PUFA), mainly docosahexaenoic acid 22:6ω3 (DHA), in the development and function of the brain and visual system is well established. DHA, the most abundant omega-3 PUFA in the vertebrate brain, contributes to neuro- and synaptogenesis, neuronal differentiation, synaptic transmission and plasticity, neuronal network formation, memory and behaviour formation. Based on these data, the unique importance of DHA and its irreplaceability in neural and retinal tissues has been postulated. In this review, we consider omega-3 PUFA composition in the brain and retina of various invertebrates, and show that DHA has only been found in marine mollusks and crustaceans. A gradual decrease in the DHA content until its disappearance can be observed in the brain lipids of the series marine-freshwater-terrestrial crustaceans and marine-terrestrial mollusks, suggesting that the transition to the land lifestyle in the evolution of invertebrates, but not vertebrates, was accompanied by a loss of DHA. As with terrestrial crustaceans and mollusks, DHA was not found in insects, either terrestrial or aquatic, or in nematodes. We show that the nervous and visual systems of various DHA-free invertebrates can be highly enriched in alpha-linolenic acid 18:3ω3 or eicosapentaenoic acid 20:5ω3, which affect neurological and visual function, stimulating synaptogenesis, synaptic transmission, visual processing, learning and even cognition. The review data show that, in animals at different levels of organization, omega-3 PUFA are required for the functioning of the nervous and visual systems and that their specific needs can be met by various omega-3 PUFA.