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Correlative analysis of endogenous miRNA expression profiles underlying brown planthopper adaptation to resistant rice.

The brown planthopper (Nilaparvata lugens Stål, BPH) is a major insect pest threatening global rice production. However, the molecular mechanisms underlying the adaptation of BPH populations with different virulence levels to resistant rice cultivars remain poorly understood. MicroRNAs (miRNAs), as key post-transcriptional regulators, play critical roles in host adaptation in herbivorous insects. In this study, we analyzed the miRNA expression profiles of a high-virulent population (IR56p) and a low-virulence population (TN1p) after feeding on susceptible (TN1) and resistant (IR56) rice cultivars. Our findings reveal distinct miRNA-mediated regulatory strategies employed by the two populations. The IR56p population showed downregulation of miRNAs including miR-10, miR-124, and miR-316, showing an inverse correlation with increased expression of predicted target genes involved in detoxification (carboxylesterase, UDP-glycosyltransferase) and effector function (calmodulin). In contrast, several miRNAs highly expressed in IR56p, including miR-307, miR-317, and miR-275, were predicted to target rice genes associated with hormone signaling, cell wall biosynthesis, and oxidative homeostasis, suggesting a possible but unproven inter-species regulatory role that requires functional validation. Collectively, these descriptive and correlative findings provide hypothesis generating insights into insect-plant coevolution and identifies candidate molecular targets for future functional validation and RNA interference-based pest management strategies.

Animals

Muscular fiber properties and multi-omics investigation of larval and adult locomotor muscle in Microhyla fissipes.

During metamorphosis, Microhyla fissipes undergoes a critical transition from an aquatic to a terrestrial lifestyle, accompanied by significant remodeling of skeletal muscle. Notably, larval tail muscle degenerates, while adult hindlimb muscle develops. However, the molecular mechanisms that orchestrate these muscle type-specific adaptations to the changing environment remain unclear. In this study, histological observation, transcriptomics, and metabolomics were integrated to compare locomotor muscles from two stages: larval muscle from tail versus adult muscle from hindlimb. Our results revealed that adult muscle fibers exhibited reduced diameter and shorter sarcomere length compared to those of tadpoles. Transcriptomic analysis identified 4103 differentially expressed genes (DEGs), including 2182 up-regulated and 1921 down-regulated genes. Up-regulated genes were mainly involved in energy metabolism and cellular homeostasis pathways, including PPAR signaling and oxidative phosphorylation, whereas down-regulated genes were associated with carbohydrate metabolism and cell proliferation pathways, such as glycolysis/gluconeogenesis and PI3K-Akt signaling. Metabolic profiling indicated a metabolic shift from anaerobic to aerobic energy production, with 57 differential metabolites identified, mainly involved in protein metabolism and insulin-related pathways. Integrated multi-omics analysis further highlighted the AMPK and FoxO signaling pathways play key roles in this process. In conclusion, our findings demonstrate that the metabolic and structural differences between larval and adult skeletal muscles are mediated by AMPK- and FoxO-dependent signaling pathways, providing novel insights into the molecular mechanisms underlying adaptive development and locomotor transition in anuran amphibians.

Animals

Genome-wide identification of the HSP70 superfamily in tropical sea cucumber Stichopus monotuberculatus and their expression analysis under low-salinity stress.

Heat shock proteins (HSPs) are a group of evolutionarily conserved molecular chaperones that serve as indispensable core regulators in preserving cellular homeostasis and orchestrating organismal stress responses. The tropical sea cucumber Stichopus monotuberculatus, a high-value aquaculture species, is sensitive to fluctuations in environmental salinity-a challenge that has emerged as a critical bottleneck limiting its large-scale commercial cultivation. However, no systematic investigation has been conducted to characterize the HSP70 superfamily in S. monotuberculatus and elucidate its functional roles in salinity adaptation. In the present study, we performed a comprehensive genome-wide scan and identified 19 HSP70 superfamily genes in the S. monotuberculatus genome, with the HSP70IV subfamily showing remarkable gene expansion, containing 8 distinct copies. Phylogenetic analysis, conserved motif identification, and gene structure characterization demonstrated high evolutionary conservation within each HSP subfamily. These genes were unevenly distributed across the chromosomes of S. monotuberculatus, and prediction of cis-acting elements revealed that their upstream regulatory regions were enriched with numerous functional elements associated with stress response and immune regulation. Salinity stress experiments revealed that under severe low-salinity conditions (18‰), the expression levels of SmHSPA14L and multiple HSP70IV subfamily members were significantly elevated, while SmHYOU1D was significantly downregulated; in contrast, only subtle changes were detected in the expression of most HSP70 genes under moderate low-salinity stress (24‰). These findings strongly suggest that HSP70 genes, particularly the expanded HSP70IV subfamily, may act as key modulators in the low-salinity stress response. This work provides valuable insight into the molecular mechanisms underlying salinity adaptation in tropical sea cucumbers.

Animals

Desert-derived Ensifer sp. SA403 enhances potato salt tolerance by reshaping rhizosphere microbiome functions and host responses.

Soil salinization increasingly threatens global food security, and potato (Solanum tuberosum L.), a moderately salt-sensitive crop, is particularly vulnerable to saline soils. Plant growth-promoting rhizobacteria (PGPR) offer a promising strategy to improve crop performance, yet how PGPR interact with native microorganisms to enhance potato salt tolerance remains poorly understood. In this study, we identified a desert-derived PGPR strain, Ensifer sp. SA403, which substantially enhanced potato performance under high salinity across sterile, non-sterile and field conditions. Physiologically, inoculation with SA403 reduced shoot Na⁺ accumulation and increased the K⁺/Na⁺ ratio; notably, these effects were markedly stronger in non-sterile substrates than under sterile conditions, indicating that SA403-mediated ion homeostasis relies on cooperation with the resident microbiota rather than on the strain acting alone. Metagenomic profiling indicated that SA403 strain reshaped rhizosphere communities, significantly enriching beneficial taxa such as Priestia and Bradyrhizobium, and upregulated functional pathways involved in glutathione and sulfur metabolism. Furthermore, host transcriptomic analyses showed that SA403 modulated plant responses to salt stress, with differentially expressed genes enriched in jasmonic acid signaling, ethanolamine metabolism and amino-acid biosynthesis pathways. Field trials on saline soils confirmed that SA403 significantly increased seedling emergence and tuber weight. Together, our results demonstrate that SA403 functions as a biological mediator that optimizes rhizosphere microecology and coordinates ion balance and host signaling to enhance potato salt tolerance. These findings support the potential of SA403 as a robust PGPR-based tool for sustainable potato production on saline soils.

Rhizosphere

Multi-omics analysis reveals stage-associated differences in gut immunity and microbiota between juvenile and adult common carp (Cyprinus carpio).

In vertebrates, the development of intestinal immunity is closely associated with dynamic changes in the gut microbiota. However, stage-associated differences in intestinal immunity and gut microbial communities remain poorly characterized in teleost fish. In this study, transcriptomic analysis combined with 16S rRNA gene sequencing was employed to characterize intestinal immunity and gut microbial communities in juvenile and adult common carp (Cyprinus carpio). Transcriptomic profiling revealed marked developmental differences in intestinal immune function. Juvenile carp exhibited a predominantly innate immune phenotype, characterized by elevated expression of pro-inflammatory cytokines, antimicrobial peptides, and lysozyme-related genes. This immune profile was accompanied by enhanced mucosal barrier function and a relatively pro-inflammatory intestinal environment. In contrast, adult carp displayed increased expression of genes associated with adaptive immunity, suggesting that adult common carp exhibit relatively stronger adaptive immune characteristics than juvenile fish. Gut microbiota analysis demonstrated significant stage-dependent differences in microbial diversity and community composition. Juvenile fish were enriched with bacterial taxa potentially associated with innate immune activation, whereas adult fish harbored distinct microbial communities linked to intestinal homeostasis and barrier maintenance. Furthermore, correlation analyses identified significant associations between specific microbial taxa and innate immune-related gene expression, suggesting a close association between gut microbiota composition and intestinal immune characteristics in juvenile and adult common carp. Collectively, these findings reveal stage-associated differences in intestinal immunity and gut microbial communities between juvenile and adult common carp, thereby providing insights into intestinal immune characteristics at different developmental stages in teleost fish.

Animals

Improved comprehensive profiling of fecal bile acids through chemical derivatization combined with HPLC-MS/MS analysis.

Bile acids (BAs) facilitate the digestion and absorption of fats and influence lipid and glucose homeostasis, making them potential therapeutic targets for obesity and related metabolic disorders. The liver and intestinal microbiota modify BAs structurally, generating diverse chemical forms and isomers. Comprehensive profiling of the BA pool is critical for understanding their key biological functions and as a therapeutic approach for related diseases. High-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) is usually chosen as the preferred method for BA detection due to the complex chemical structures, the wide range of actual concentrations and the complexity of fecal sample matrices. However, free BAs are difficult to ionize, resulting in low detection signals and a lack of characteristic structural fragments to assist in structural identification. In this method, the labeling reagent (2-aminoethyl) trimethylammonium (AETMA) is employed to label the carboxyl group of BAs. Compared with underivatized BAs, the detection sensitivity of unconjugated BAs was enhanced by 25-180 fold, while that of conjugated BAs increased by 6-160 fold. It also generates unique fragment ions and enhances MS response, facilitating the discovery of potential BAs. Methodological parameters were validated using 38 BAs as representatives. Through methodological validation, it was verified that the precision, recovery, matrix effect and stability parameters of the method met acceptable criteria. We also identified 61 confirmed BAs and 55 additional candidate BAs in human pooled fecal samples. It has been successfully applied to fecal BA analysis in obese populations, providing valuable insights into potential therapeutic strategies for obesity.

Tandem Mass Spectrometry

Multi-omics insights into the physiological mechanisms of bile acid accumulation in the gallbladder in brumation-like snakes.

Hibernation/brumation represents an important physiological adaptation for animals to cope with seasonal environmental changes. Field observations suggested increased gallbladder weight in the Five-pacer viper (Deinagkistrodon acutus) during brumation, and our quantitative measurements confirmed this increase together with bile acid accumulation. By integrating a multi-omic approach, this study elucidates the regulatory mechanisms of bile acid accumulation in the gallbladder during brumation. Results showed that taurocholic acid (TCA) and taurodeoxycholic acid (TDCA) were the major components in the gallbladder of the brumation-like group, with significantly elevated concentrations of bile acids, whereas bile acid concentrations in serum and intestinal contents were markedly reduced, indicating suppression of the enterohepatic circulation and consequent accumulation of bile acids in the gallbladder. Hepatic transcriptomic analysis revealed significant downregulation of bile acid synthesis and regulatory genes in brumation-like snakes. In contrast, the alternative synthesis pathway gene sterol 27-hydroxylase (CYP27A1) and some transporter genes were slightly upregulated. Further, some modification genes and regulatory genes showed no significant differences between active and brumation-like states. Gut microbiota analysis demonstrated Akkermansia muciniphila, Bacteroides fragilis, and Citrobacter freundii were more enriched in the active group, which were common microbes related to bile acid metabolism, and the correlation analysis confirmed this relationship. Taken together, these findings indicate that the "physiological bile acid accumulation" observed in snakes during brumation-like state is jointly driven by suppressed hepatic synthesis, reduced enterohepatic circulation, and remodeled microbial community structure. The study provides novel comparative physiological insights into extreme metabolic homeostasis in animals.

Animals

Occupationally relevant vibrations and the brain: frequency-dependent proteomics signatures in a rat model.

INTRODUCTION: Occupational exposure to whole-body vibration (WBV), particularly in agricultural environments, has been associated with adverse cognitive and physiological effects. This study examined the neurophysiological impact of WBV in a rat model at 4 Hz and 30 Hz, frequencies representative of off-road and on-road vehicle operation. METHODOLOGY: Forty-four Sprague-Dawley rats were assigned to control (0 Hz), low-frequency (4 Hz), or high-frequency (30 Hz) vibration conditions. After three days of exposure, brain tissues were collected and analyzed using mass spectrometry-based proteomics to identify differentially expressed proteins. RESULTS: Proteomic profiling revealed distinct, frequency-dependent alterations in brain protein expression. Compared with controls, 32 cognition-related proteins were differentially regulated at 4 Hz and 29 at 30 Hz, with 13 differing between the two vibration conditions. Principal component analysis showed clear separation among groups, indicating unique proteomic signatures for each exposure frequency. Functional enrichment and protein-protein interaction analyses demonstrated involvement of synaptic plasticity, cytoskeletal organization, calcium regulation, and neurotransmitter release. Exposure to 4 Hz was associated with the upregulation of proteins involved in calcium homeostasis and synaptic integrity, suggesting potential disruption of cognitive processes. In contrast, 30 Hz increased the expression of proteins related to axonal guidance and neuroprotection, indicating a less clearly adverse response that may reflect adaptive or potentially beneficial effects. DISCUSSION: These findings provide new insight into biological mechanisms underlying WBV-induced cognitive changes and underscore the importance of vibration frequency in shaping neurophysiological outcomes. They also establish a foundation for future studies integrating proteomics with behavioural assessments in animals and humans.

Animals

Evolutionary conservation of heat shock proteins in Blattodea and their roles in wing morphogenesis and ovarian development of Blattella germanica.

Heat shock proteins (Hsps) are essential molecular chaperones for protein homeostasis and stress responses. However, the Hsp repertoires and functions in Blattodea remain underexplored. Our genome-scale survey of nine Blattodea species revealed 37-46 conserved Hsp90, Hsp70, and DNAJ (Hsp40) genes, with DNAJ the most abundant and Hsp90 the least. Phylogenetic analysis confirmed the evolutionary conservation of three Hsp90, seven Hsp70, and 29 DNAJ subclades in Blattodea. Selection pressure analysis revealed predominant purifying selection (dN/dS ≪ 1) across lineages, strongest in DNAJ and highest in Hsp90 conservation. In Blattella germanica, expression of six representative BgHsp genes progressively increased during development, peaking in fifth-instar nymphs. Tissue expression profiling revealed that BgHspA1-2/3/4 were predominantly expressed in legs, BgDNAJB5 and BgHsp90AB1-2 were enriched in the fat body, and BgHsp90AB1 was highly expressed in the head. dsRNA injection targeting conserved Hsp gene regions achieved 61.9-94.1% knockdown of all six target genes. RNAi knockdown of six BgHsp genes disrupted wing morphogenesis, causing distinct phenotypes: wing whitening (56.7%, dsBgHspA1-4), unequal length (66.7%, dsBgHspA1-3; 76.7%, dsBgDNAJB5), and wing wrinkling (70%, dsBgHspA1-2; 63.3%, dsBgHsp90AB1; 76.7%, dsBgHsp90AB1-2). During ovarian formation, the developmental delay was most severe in the dsBgHsp90AB1 group, moderate in the dsBgHsp90AB1-2 and dsBgHspA1-2/3/4 groups, and weakest in the dsBgDNAJB5 group. Besides, knockdown significantly downregulated key developmental genes (apterous-a, nubbin, scalloped, ultrabithorax, wingless, and vitellogenin). These findings provide a reference for understanding the evolutionary patterns of Hsps in Blattodea, and offer mechanistic insights into the developmental regulation mediated by Hsps in this important public-health pest.

Animals

Lipid metabolism is a key central, systemic and gut microbial feature of the decline in rat hippocampal function during middle age.

Middle age is emerging as a turning point in brain ageing, prognostic of future cognitive health and amenable to intervention. Metabolic and proteomic differences during this period are not yet fully understood and may potentially influence functions of the hippocampus, a brain area that regulates memory and anxiety. While the gut microbiota is implicated in brain ageing, the relationship between the gut microbiota, the metabolic state, and hippocampal proteome in middle age has not been investigated. We hypothesise that peripheral metabolic or protein features are associated with hippocampal vulnerability in middle age. Therefore, young adult and middle-aged rats were assessed for behavioural, proteomic, metabolic, and gut microbiota differences. Proteomic profiling of the hippocampus revealed differential expression of proteins indicative of altered synaptic signalling. Concurrently, adult hippocampal neurogenesis was decreased in middle age. Hippocampal microglia exhibited a lipid rich, inflammatory phenotype in middle age which correlated with poorer memory performance. CSF and serum proteomic and metabolomic analyses identified dysregulated lipid-related pathways potentially contributing to hippocampal vulnerability in middle age. Furthermore, 16S rRNA sequencing revealed reduced abundance of bacteria involved in lipid metabolism regulation. However, faecal microbiota transfer from young to middle aged rats was not sufficient to robustly improve hippocampus-dependent spatial memory. Together, these findings highlight dysfunctional lipid metabolism as a key feature of middle age that may contribute to decline in hippocampal function. Given that the scope for intervention is limited during older age, targeting biomarkers involved in metabolic and lipid homeostasis may be pivotal for the development of pharmacological or lifestyle-based interventions during middle age which could ultimately delay future cognitive ageing.

Animals

Fatty acids and breast cancer: Epidemiology, subtype-specific metabolism, immune regulation, and clinical translation.

Fatty acids (FAs) are bioactive dietary and metabolic molecules that participate in membrane architecture, energy homeostasis, inflammatory signaling, gene regulation and immune function, all of which intersect with breast cancer (BC) risk, progression and treatment response. In this narrative review we integrate epidemiological, clinical, translational and mechanistic evidence on the role of FAs in BC. Saturated, monounsaturated, trans- and polyunsaturated FAs (PUFAs) are treated as distinct biological exposures rather than interchangeable measures of total fat intake. Similarly, evidence from dietary assessment, circulating biomarkers, erythrocyte membrane composition, adipose tissue stores and tumor lipid signatures is interpreted separately, because each captures exposure and biology at a different level. BC subtypes differ in FA synthesis, uptake, oxidation, storage and remodeling: luminal tumors are frequently linked to hormone-regulated lipogenesis, human epidermal growth factor receptor 2 (HER2)-positive tumors to growth-factor-driven lipid metabolism, and triple-negative tumors to exogenous FA uptake, inflammatory lipid mediators and ferroptosis-related vulnerabilities. FA-derived mediators also shape immune-cell polarization, cytokine signaling and the tumor microenvironment, and dietary FAs may reshape the gut microbiota; the fiber-derived short-chain FAs it produces, distinct from dietary FAs, likewise help regulate immune and inflammatory tone. Clinical data suggest possible roles for fat-quality modification and selected n-3 PUFA interventions, but findings are heterogeneous and not yet sufficient to support routine biomarker-guided precision onco-nutrition. Candidate biomarkers, such as erythrocyte n-6:n-3 composition, require prospective validation before clinical implementation. FA biology thus represents a modifiable but complex axis in BC prevention, tumor biology and supportive care.

Humans

Transcriptomic and RNAi analyses reveal chloride channel 3-associated osmoregulation in Litopenaeus vannamei under low-salinity stress.

Chloride channels and transporters are important for cellular volume regulation and salinity adaptation in euryhaline crustaceans, yet the intestinal transcriptional relationship between plasma-membrane and intracellular chloride pathways remains unclear in Litopenaeus vannamei. In this study, RNA interference of anoctamin 1 (ANO1) was combined with intestinal transcriptome sequencing under the production-relevant low-salinity condition of salinity 3. ANO1 silencing produced a focused transcriptional response, with 16 differentially expressed genes (DEGs) identified (11 upregulated and 5 downregulated). Functional enrichment indicated that these genes were associated with transporter activity, cytoskeletal organization, extracellular matrix-receptor interaction, membrane lipid metabolism, and vesicular processes. Notably, a transcript encoding chloride channel protein 3 (CLC-3) was significantly upregulated following ANO1 knockdown, suggesting a potential transcriptional relationship between ANO1 and CLC-3 in chloride homeostasis. Based on this finding, CLC-3 was selected for full-length cDNA cloning, sequence characterization, salinity-gradient expression analysis, and RNAi-based functional assessment. The cloned CLC-3 cDNA was 2883 bp in length and encoded an 850 amino acid protein containing a conserved voltage-gated chloride channel (Voltage-CLC) domain and two cystathionine β-synthase domains. Phylogenetic analysis placed LvCLC-3 within the intracellular CLC-c clade, and tissue distribution analysis showed the highest CLC-3 expression in the intestine. Intestinal CLC-3 expression responded nonlinearly to salinity variation, peaking at salinity 20. Under salinity 3, CLC-3 knockdown reduced ANO1, Na+/K+-ATPase alpha subunit, and Na+-K+-2Cl- cotransporter transcript levels, whereas glutamate-gated chloride channel expression increased. Mild hepatopancreatic structural alterations were also observed after CLC-3 knockdown. These findings suggest that CLC-3 is a salinity-responsive intracellular chloride-transporter candidate associated with intestinal ion-transport-related transcriptional responses after ANO1 suppression in L. vannamei, although the underlying physiological mechanism requires further validation.

Animals

Early hepatic protein responses to dietary restriction-refeeding in Japanese quail: A proteomic investigation.

Feed intake and refeeding after nutrient scarcity induce rapid metabolic adaptations in the poultry liver; however, hepatic proteomic recovery pathways in the early hours post-refeeding remain poorly defined. This study aimed to characterize early liver protein signatures in Japanese quail (Coturnix japonica) recovering from nutritional stress under two refeeding conditions. Eighteen 12-week-old male quails (245.20 ± 0.213 g) were assigned to three groups (n = 6): control fed ad libitum (12.13 MJ/kg), 24 h feed deprivation followed by 6 h refeeding, and 24 h low metabolizable energy (6.30 MJ/kg) diet followed by 6 h refeeding. In total, 854 proteins were identified, of which 515 met the filtering criteria. The low metabolizable energy refeeding showed higher abundance of proteins linked to ATP binding and carbohydrate/carboxylic acid metabolism, alongside detoxification-related proteins, while suppressing translation/RNA-binding machinery and antioxidant pathways. Feed-deprived refeeding enriched in oxidative phosphorylation and mitochondrial complex I assembly with reduced cytoplasmic translation, NMD-related components, and sulfur compound metabolism. A direct comparison indicated divergent recovery strategies: low metabolizable energy refeeding mainly reflected oxidoreductase activity and translation initiation, whereas feed-deprived refeeding potentially enriched mitochondrial ATP production and glutathione-based defenses. Our analysis indicate that 6 h of refeeding initiates an early, incomplete recovery toward hepatic homeostasis, with the severity of prior nutritional restriction dictating distinct liver metabolic priorities. Collectively, these findings might provide a preliminary understanding of the hepatic mechanisms involved in recovery from nutrient deprivation and may help in the development of feeding strategies for managing metabolic recovery in poultry. However, these findings should be considered hypothesis-generating pending further validation.

Animals

Norgestrel drives mitochondrial collapse and plasma membrane impairment in Pacific oyster (Crassostrea gigas) sperm by triggering premature acrosome reaction.

The toxic mechanisms of norgestrel (NGT), an emerging marine pollutant, on the sperm from externally fertilized invertebrates remain elusive. This study employed an integrated physiological and multi-omics framework to elucidate how NGT (10 and 1000 ng/L) disrupts acrosome reaction (AR) signaling machinery, thereby impairing the functional integrity of Pacific oyster (Crassostrea gigas, also known as Magallana gigas) sperm. Exposure to NGT triggered a significant, dose-dependent premature AR, characterized by elevated acrosin activity and a loss of acrosomal integrity. Multi-omics integration supports a model in which this premature exocytosis is linked to signaling disturbances, including disruption of calcium signaling and reduced transcript abundance of calmodulin (CaM) and the primary recognition protein zonadhesin (Zan). This signaling interference induced an premature AR, subsequently driving a cascade of bioenergetic and structural failures. At the mitochondrial level, NGT induced abnormal mitochondrial permeability transition pore (mPTP) opening and elevated the transcript levels of antioxidant defense genes (e.g., peroxiredoxin-5, PRDX5). These alterations indicate the occurrence of mitochondrial collapse. Concurrently, scanning electron microscopy verified localized plasma membrane wrinkling and pore formation in sperm. In addition, NGT exposure decreased the transcript abundance of cytoskeleton-related genes, including solute carrier family 26 member 6 (SLC26A6), actin (ACT), and tubulin polymerization promoting protein family member 3 (TPPP3). These molecular changes further disrupted membrane phospholipid homeostasis, as represented by altered glycerophospholipid metabolism. At the same time, cumulative cellular stress was associated with decreased transcript abundance of cytoprotective factors (e.g., baculoviral IAP repeat-containing proteins, birc2) and changes in apoptosis-related genes consistent with activation of a caspase-8-mediated apoptotic programme. In conclusion, NGT, as a representative synthetic progestin, exerts reproductive toxicity by interfering with signaling mediators to induce premature AR, which subsequently exhausts metabolic energy and triggers plasma membrane impairment. These findings provide a critical mechanistic basis for the aquatic ecological risk assessment of synthetic progestins.

Animals

Genome-wide identification and expression profiling of HSD3B and SDR42E1 genes in the Pacific oyster (Crassostrea gigas): potential associations with gonadal development.

Sex steroids are lipid-soluble signaling molecules that regulate sex differentiation, reproductive development and physiological homeostasis in animals. 3β-Hydroxysteroid dehydrogenase/Δ5-Δ4 isomerase (3β-HSD) is a key steroidogenic enzyme, whereas SDR42E1, an extended short-chain dehydrogenase/reductase, has been implicated in sterol- and steroid-related metabolism. However, the composition, evolutionary relationships and expression patterns of the HSD3B- and SDR42E1-related genes in bivalve gonadal development remain poorly characterized. In this study, five PF01073-containing genes, comprising three CgHsd3b and two CgSdr42e1 genes, were identified in the Pacific oyster Crassostrea gigas. Phylogenetic analysis separated the proteins into HSD3B-related and SDR42E1-related groups, and gene-structure and motif analyses indicated subfamily-level divergence. All five proteins retained the SDR domain but differed in exon-intron structure and motif composition. Each contained the extended-SDR TGxxGxxG motif, whereas exact classical [ST]GxxxGxG and NNAG motifs were absent. Tyr- and Lys-equivalent residues were conserved, while the HSD3B1 Ser-equivalent position contained Thr in two C. gigas proteins and Ser in one. These features support their classification as extended-SDR proteins but do not establish enzymatic activity or substrate specificity. The three CgHsd3b genes were dispersed on one chromosome, whereas CgSdr42e1-1 and CgSdr42e1-2 were adjacent on another chromosome, suggesting a possible local duplication event for the CgSdr42e1 pair. Public RNA-seq data showed distinct tissue- and gonadal-stage expression patterns, with several genes displaying gonad-biased or female-stage-associated expression. Independent RT-qPCR profiling of the representative genes CgHsd3b-3 and CgSdr42e1-1 detected stage-dependent expression, although tissue rankings differed from those in the public RNA-seq datasets. These differences may reflect the use of independent biological samples, tissue composition, normalization procedures, and platform-specific measurements. Because enzymatic assays, metabolite measurements, cellular localization, and functional perturbation were not performed, the results identify candidate genes whose expression is associated with gonadal development rather than demonstrating regulatory roles. This study provides a comparative framework for future functional investigation of sterol- and steroid-related metabolism in bivalves.

Animals