Comparative Biochemistry and Physiology A-Molecular & Integrative Physiology最新文献

In the face of climate change, understanding the metabolic responses of vulnerable animals to abiotic stressors like anurans is crucial. Water restriction and subsequent dehydration is a condition that can threaten populations and lead to species decline. This study examines metabolic variations in the subtropical frog Boana pulchella exposed to dehydration resulting in a 40% loss of body water followed by 24 h of rehydration. During dehydration, the scaled mass index decreases, and concentrations of metabolic substrates alter in the brain and liver. The activity of antioxidant enzymes increases in the muscle and heart, emphasizing the importance of catalase in the rehydration period. Glycogenesis increases in the muscle and liver, indicating a strategy to preserve tissue water through glycogen storage. These findings suggest that B. pulchella employs specific metabolic mechanisms to survive exposure to water restriction, highlighting tissue-specific variations in metabolic pathways and antioxidant defenses. These findings contribute to a deeper understanding of anuran adaptation to water stress and emphasize the importance of further research in other species to complement existing knowledge and provide physiological tools to conservation.

Body temperature (Tb) variation and environmental temperature gradients are more intense in small individuals because their body size allows for a more intimate relationship between Tb and the environment. To contribute to a methodological consensus on the ecophysiology of small ectotherms, we aimed to investigate whether different approaches and methodological techniques affect the measurement of critical temperatures in a small lizard (Coleodactylus meridionalis, Sphaerodactylidae) from the Atlantic Forest of southern Bahia, Brazil, and subsequently its vulnerability assessment. We measured two metrics of thermal physiology: critical thermal minimum (CTmin) and critical thermal maximum (CTmax). In total, four types of temperature measurements (protocols) were defined. In the first protocol, we estimated CTmax/CTmin without heating/cooling rate by directly measuring the lizard's midbody temperature. In the other three protocols, we used a ramping assay with a heating/cooling rate to estimate CTmax/CTmin in the chamber (height: 11.3 cm), substrate, and Tb of the lizard, respectively. In total 116 individuals of Coleodactylus meridionalis were collected, of which 177 CTmax and 131 CTmin were performed. C. meridionalis showed a mean CTmax of 41 °C and a mean CTmin of 8.9 °C when considering the Tb protocol, which is intermediate compared to the other protocols. The substrate temperature protocol was the closest to Tb, and for this, the best method for the small lizards using an infrared thermometer.

The growth hormone (GH)-insulin-like growth factor-1 (IGF-1) system regulates skeletal muscle growth and function. GH has a major function of targeting the liver to regulate IGF-1 production and release, and IGF-1 mediates the primary anabolic action of GH on growth. However, skeletal muscle is a target tissue of GH as evidenced by dynamic GH receptor expression, but it is unclear if GH elicits any direct actions on extrahepatic tissues as it is difficult to distinguish the effects of IGF-1 from GH. Fish growth regulation is complex compared to mammals, as genome duplication events have resulted in multiple isoforms of GHs, GHRs, IGFs, and IGFRs expressed in most fish tissues. This study investigated the potential for GH direct actions on fish skeletal muscle using an in vitro system, where rainbow trout myogenic precursor cells (MPCs) were cultured in normal and serum-deprived media, to mimic in vivo fasting conditions. Fasting reduces IGF-1 signaling in the muscle, which is critical for disentangling the roles of GH from IGF-1. The direct effects of GH were analyzed by measuring changes in myogenic proliferation and differentiation genes, as well as genes regulating muscle growth and proteolysis. This study provides the first in-depth analysis of the direct actions of GH on serum-deprived fish muscle cells in vitro. Data suggest that GH induces the expression of markers for proliferation and muscle growth in the presence of serum, but all observed GH action was blocked in serum-deprived conditions. Additionally, serum deprivation alone reduced the expression of several proliferation and differentiation markers, while increasing growth and proteolysis markers. Results also demonstrate dynamic gene expression response in the presence of GH and a JAK inhibitor in serum-provided but not serum-deprived conditions. These data provide a better understanding of GH signaling in relation to serum in trout muscle cells in vitro.

Mitochondrial function can be regulated by ion channels. Mitochondrial RNA splicing 2 (Mrs2) is a magnesium ion (Mg²⁺) channel located in the inner mitochondrial membrane, thereby mediating the Mg²⁺ influx into the mitochondrial matrix. However, its potential role in regulating the Mg homeostasis and mitochondrial function in aquatic species is still unclear. This study molecularly characterizes the gene encoding Mrs2 in fish M. amblycephala with its functions in maintaining the Mg homeostasis and mitochondrial function verified. The mrs2 gene is 2133 bp long incorporating a 1269 bp open reading frame, which encodes 422 amino acids. The Mrs2 protein includes two transmembrane domains and a conserved tripeptide Gly-Met-Asn, and has a high homology (65.92–97.64%) with those of most vertebrates. The transcript of mrs2 was relatively high in the white muscle, liver and kidney. The inhibition of mrs2 reduces the expressions of Mg²⁺ influx/efflux-related proteins, mitochondrial Mg content, and the activities of mitochondrial complex I and V in hepatocytes. However, the over-expression of mrs2 increases the expressions of Mg²⁺ influx/efflux-related proteins, mitochondrial Mg content, and the complex V activity, but decreases the activities of mitochondrial complex III and IV and citrate synthase in hepatocytes. Collectively, Mrs2 is highly conserved among different species, and is prerequisite for maintaining Mg homeostasis and mitochondrial function in fish.

Muscle and bone are cooperatively preserved in Daurian ground squirrels (Spermophilus dauricus) during hibernation. As such, we hypothesized that IGF-1 and myostatin may contribute to musculoskeletal maintenance during this period. Thus, we systematically assessed changes in the protein expression levels of IGF-1 and myostatin, as well as their corresponding downstream targets, in the vastus medialis (VM) muscle and femur in Daurian ground squirrels during different stages. Group differences were determined using one-way analysis of variance (ANOVA). Results indicated that the co-localization levels of IGF-1 and its receptor (IGF-1R) increased by 50% during the pre-hibernation period (PRE) and by 35% during re-entry into torpor (RET) compared to the summer active period (SA). The phosphorylation level of FOXO1 in the VM muscle increased by 50% in the torpor (TOR) group and by 82% in the inter-bout arousal (IBA) group compared to the PRE group. The phosphorylation level of SGK-1 increased by 54% in the IBA group and by 62% in the RET group compared to the SA group. In contrast, the protein expression of IGF-1 and phosphorylation levels of PI3K, Akt, mTOR, and GSK3β in the VM muscle showed no obvious differences among the different groups. β-catenin protein expression was up-regulated by 84% in the RET group compared to the SA group, while the content of IGF-1 protein, correlation coefficients of IGF-1 and IGF-1R, and phosphorylation levels of PI3K, Akt, and GSK3β in the femur showed no significant differences among groups. Regarding myostatin and its downstream targets, myostatin protein expression decreased by 70% in the RET group compared to the SA group, whereas ActRIIB protein expression and Smad2/3 phosphorylation in the VM muscle showed no obvious differences among groups. Furthermore, Smad2/3 phosphorylation decreased by 58% in the TOR group and 53% in the RET group compared to the SA group, whereas ActRIIB protein expression in the femur showed no obvious differences among groups. Overall, the observed changes in IGF-1 and myostatin expression and their downstream targets may be involved in musculoskeletal preservation during hibernation in Daurian ground squirrels.

Developing chick embryos that are subjected to increased incubation temperature are more stressor-resilient later in life, but the underlying process is poorly understood. The potential mechanism may involve changes in small intestine function. In this study, we determined behavioral, morphological, and molecular effects of increased embryonic incubation temperatures and post-hatch heat challenge in order to understand how embryonic heat conditioning (EHC) affects gut function. At 4 days post-hatch, duodenum, jejunum, and ileum samples were collected at 0, 2, and 12 h relative to the start of heat challenge. In EHC chicks, we found that markers of heat and oxidative stress were generally lower while those of nutrient transport and antioxidants were higher. Temporally, gene expression changes in response to the heat challenge were similar in control and EHC chicks for markers of heat and oxidative stress. Crypt depth was greater in control than EHC chicks at 2 h post-challenge, and the villus height to crypt depth ratio increased from 2 to 12 h in both control and EHC chicks. Collectively, these results suggest that EHC chicks might be more energetically efficient at coping with thermal challenge, preferentially allocating nutrients to other tissues while protecting the mucosal layer from oxidative damage. These results provide targets for future studies aimed at understanding the molecular mechanisms underlying effects of embryonic heat exposure on intestinal function and stressor resiliency later in life.

There is a consensus that electroneutral Na⁺/H⁺ exchangers (NHEs) are important in branchial Na⁺ uptake in freshwater fish. There is also widespread belief, based on mammalian data, that EIPA [5-(N-ethyl-N-isopropyl)-amiloride]], and HMA [5-(N,N-hexamethylene)-amiloride)] are more potent and specific in blocking Na⁺ uptake than amiloride. We evaluated this idea by testing the three drugs at 10⁻⁷ to 10⁻⁴ M, i.e. 0.1 to 100 μM in two model species, rainbow trout (Oncorhynchus mykiss) and goldfish (Carassius auratus), using ²²Na⁺ to measure unidirectional Na⁺ influx and efflux rates. In both species, the potency order for inhibiting unidirectional Na⁺ influx was HMA > amiloride > EIPA (IC₅₀ values in the 10–70 μM range), very different from in mammals. At 100 μM, all three drugs inhibited Na⁺ influx by >90% in both species, except for amiloride in goldfish (65%). However, at 60–100 μM, all three drugs also stimulated unidirectional Na⁺ efflux rates, indicating non-specific effects. In trout, HMA and EIPA caused significant increases (2.1- to 2.3-fold) in efflux rates, whereas in goldfish, significant efflux elevations were greater (3.1- to 7.2-fold) with all three drugs. We conclude that the inhibitory potency profile established in mammals does not apply to the NHEs in fish gills, that non-specific effects on Na⁺ efflux rates are a serious concern, and that EIPA and HMA offer no clear benefits in terms of potency or specificity. Considering its much lower cost, we recommend amiloride as the drug of choice for in vivo experiments on freshwater fishes.

Temperature is a preeminent factor in the regulation of fish reproduction and hinders gonadal development beyond a specific threshold. To comprehend the molecular mechanism responsible for reproductive suppression at different temperature, expression of the genes encoding kisspeptin (kiss2), gonadotropin-releasing hormone (gnrh1) and their receptors (gpr54, gnrh1r) in the brain, and the gonadotropin (GTH) subunits (fshb and lhb) in the pituitary were studied in juvenile Nile tilapia (Oreochromis niloticus) along with gonadal histology. Fish were acclimatized to three distinct temperatures, including 31 °C, 34 °C and 37 °C for 14 days. The mRNA levels of kiss2, gpr54, gnrh1, and gnrh1r were significantly decreased at 37 °C compared to 31 °C and 34 °C in the both sexes. In parallel, the expression level of fshb in the both sexes and lhb in the female were significantly lower at 37 °C in the pituitary. Histologically, the gonads of both sexes had normal growth of gametes at control temperature (31 °C), whereas the spermatogenesis and oocyte maturation were slowed down and atretic oocytes were found in the ovary at 37 °C acclimation temperature. Taken together, the results imply that elevated temperature beyond the specific threshold may have a negative impact on reproduction by suppressing the gene expressions of kisspeptin/GnRH1/GTH system and eventually restrains normal growth and maturation of gametes in the both sexes of Nile tilapia.

Throughout life, animals must maintain homeostasis while coping with challenging events. The period after reproduction can be challenging for oviparous females to maintain homeostasis since they direct most of their energy stores to vitellogenesis, possibly increasing the vulnerability to stressors. Changes in glucocorticoids' (GC) secretion promote various behavioural and physiological adjustments daily and to restore balance after facing stressors. However, when GC are elevated for extended periods, which usually occurs in response to chronic exposure to stressors, they can affect feeding behaviour and suppress the immune function. We aim to elucidate the effects of chronic corticosterone (CORT) exposure on feeding behaviour, body condition and immune function in female lizards, Tropidurus catalanensis, in the post-reproductive period. Thirty animals were divided into three groups: 1. Control (no experimental procedure performed); 2. Empty Implant (animals implanted with empty silastic tube); and 3. CORT Implant (animals implanted with silastic tube filled with CORT, with a chronic continuous release for at least a week). CORT plasma levels feeding behaviour, body condition (body index [BI] and fat index [FI]), leukocyte count, and several immune function variables (bacterial killing ability [BKA], hemagglutination titer, phytohemagglutinin [PHA] immune challenge and leukocyte count) were evaluated. After implantation, CORT treated animals maintained stable body mass through the experiment, while Control and Empty Implant groups displayed weight loss. In the CORT treated animals, there was also a positive relation between BI and FI, and higher FI when compared to groups 1 and 2. No effects of CORT were observed on feeding behaviour nor on the immune function.

A meta-analytic approach deciphered the taxonomic profile of the zebrafish gut microbiota at different developmental stages. Data (16S rDNA) were systematically searched in databases, selecting those with intestine samples of fish not exposed to a particular treatment or challenge (e.g., pathogens, dietetic tests, xenobiotics, etc.) and obtaining 340 samples to be processed. Results revealed marked differences between the developmental phases. Proteobacteria was the dominant phylum in the larval phase, with a relative abundance of 90%, while the rest of the phyla did not exceed 2%. Vibrio, Aeromonas, Plesiomonas, Pseudomonas, Shewanella, and Acinetobacter were the dominant genera in this phase. Transitional changes were observed after the larvae stage. Proteobacteria still registered high abundance (48%) in the juvenile phase, but Fusobacteria (40%) and Bacteriodota (5.9%) registered considerable increases. Genera, including Cetobacterium, Plesiomonas, Aeromonas, Vibrio, and Flavobacterium, dominated this stage. The phyla Proteobacteria (48%) and Fusobacteria (35%) were strongly established in the adult phase. Cetobacterium was registered as the most abundant genus, followed by Aeromonas, Acinetobacter, Plesiomonas, Vibrio, and ZOR0006 (Firmicutes; 6%). In conclusion, the composition of the intestinal microbiota of zebrafish is consistently determined by two primary phyla, Proteobacteria and Fusobacteria; however, this composition varies depending on the developmental stage. Cetobacterium and Aeromonas are the most relevant genera in juveniles and adults. Finally, these results reveal a consistent pattern of certain bacterial groups in the zebrafish microbiota that could help shape gnotobiotic models (colonized with a specific known bacterial community) or synthetic microbiota (in vitro assembly of microbes), among other approaches.