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Histones and their N-terminal or C-terminal derived peptides have been studied in vertebrates and presented as potential antimicrobial agents playing important roles in the innate immune defenses. Although histones and their derived peptides had been reported as components of innate immunity in invertebrates, the knowledge about the histone derived antimicrobial peptides (HDAPs) in invertebrates are still limited. Using a peptidomic technique, a set of peptide fragments derived from the histones was identified in this study from the serum of microbes challenged Mytilus coruscus. Among the 85 identified histone-derived-peptides with high confidence, 5 HDAPs were chemically synthesized and the antimicrobial activities were verified, showing strong growth inhibition against Gram-positive bacteria, Gram-negative bacteria, and fungus. The gene expression level of the precursor histones matched by representative HDAPs were further tested using q-PCR, and the results showed a significant upregulation of the histone gene expression levels in hemocytes, gill, and mantle of the mussel after immune stress. In addition, three identified HDAPs were selected for preparation of specific antibodies, and the corresponding histones and their derived C-terminal fragments were detected by Western blotting in the blood cell and serum of immune challenged mussel, respectively, indicating the existence of HDAPs in M. coruscus. Our findings revealed the immune function of histones in Mytilus, and confirmed the existence of HDAPs in the mussel. The identified Mytilus HDAPs represent a new source of immune effector with antimicrobial function in the innate immune system, and thus provide promising candidates for the treatment of microbial infections in aquaculture and medicine., Competing Interests: Declaration of competing interest The authors have declared that no conflict of interests exist., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Mytilus coruscus is an economically important marine bivalve that lives in estuarine sea areas with seasonal coastal acidification and frequently suffers shell injury in the natural environment. However, the molecular responses and biochemical properties of Mytilus under these conditions are not fully understood. In the present study, we employed tandem mass spectrometry combined with isobaric tagging to identify differentially expressed proteins in the mantle tissue of M. coruscus under different short-term treatments, including shell-complete mussels raised in normal seawater (pH 8.1), shell-damaged mussels raised in normal seawater (pH 8.1), and acidified seawater (pH 7.4). A total of 2694 proteins were identified in the mantle, and analysis of their relative abundance from the three different treatments revealed alterations in the proteins involved in immune regulation, oxidation-reduction processes, protein folding and processing, energy provision, and cytoskeleton. The results obtained by quantitative proteomic analysis of the mantle allowed us to delineate the molecular strategies adopted by M. coruscus in the shell repair process in acidified environments, including an increase in proteins involved in oxidation-reduction processes, protein processing, and cell growth at the expense of proteins involved in immune capacity and energy metabolism. SIGNIFICANCE: The impact of global ocean acidification on calcifying organisms has become a major ecological and environmental problem in the world. Mytilus coruscus is an economically important marine bivalve living in estuary sea area with seasonal coastal acidification, and frequently suffering shell injury in natural environment. Molecular responses of M coruscus under the shell damage and acute acidification is still largely unknown. For this reason, iTRAQ based quantitative proteomic and histological analysis of the mantle from M. coruscus under shell damage and acute acidification were performed, for revealing the proteomic response and possible adaptation mechanism of Mytilus under combined shell damage and acidified sea water, and understanding how the mussel mantle implement a shell-repair process under acidified sea water. Our study provides important data for understanding the shell repair process and proteomic response of Mytilus under ocean acidification, and providing insights into potential adaptation of mussels to future global change., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Growth is a fundamental aspect of aquaculture breeding programs, pivotal for successful cultivation. Understanding the mechanisms that govern growth and development differences across various stages can significantly boost seedling production of economically valuable species, thereby enhancing aquaculture efficiency and advancing the aquaculture industry. Mytilus coruscus , a commercially vital marine bivalve, underscores this importance. To decipher the intricate molecular mechanisms dictating growth and developmental disparities in marine shellfish, we conducted transcriptome sequencing and meticulously analyzed gene expression variations and molecular pathways linked to growth traits in M. coruscus . This study delved into the molecular and gene expression variations across five larval development stages, with a specific focus on scrutinizing the differential expression patterns of growth-associated genes using RNA sequencing and quantitative real-time PCR analysis. A substantial number of genes-36,044 differentially expressed genes (DEGs)-exhibited significant differential expression between consecutive developmental stages. These DEGs were then categorized into multiple pathways (Q value < 0.05), including crucial pathways such as the spliceosome, vascular smooth muscle contraction, DNA replication, and apoptosis, among others. In addition, we identified two pivotal signaling pathways-the Hedgehog (Hh) signaling pathway and the TGF-beta (TGF-β) signaling pathway-associated with the growth and development of M. coruscus larvae. Ten key growth-related genes were pinpointed, each playing crucial roles in molecular function and the regulation of growth traits in M. coruscus . These genes and pathways associated with growth provide deep insights into the molecular basis of physiological adaptation, metabolic processes, and growth variability in marine bivalves.

Mytilus coruscus is an economically important marine bivalve mollusk found in the Yangtze River estuary, which experiences dramatic pH fluctuations due to seasonal freshwater input and suffer from shell fracture or injury in the natural environment. In this study, we used intact-shell and damaged-shell M. coruscus and performed metabolomic analysis, free amino acids analysis, calcium-positive staining, and intracellular calcium level tests in the mantle to investigate whether the mantle-specific metabolites can be induced by acute sea-water acidification and understand how the mantle responds to acute acidification during the shell repair process. We observed that both shell damage and acute acidification induced alterations in phospholipids, amino acids, nucleotides, organic acids, benzenoids, and their analogs and derivatives. Glycylproline, spicamycin, and 2-aminoheptanoic acid (2-AHA) are explicitly induced by shell damage. Betaine, aspartate, and oxidized glutathione are specifically induced by acute acidification. Our results show different metabolic patterns in the mussel mantle in response to different stressors, which can help elucidate the shell repair process under ocean acidification. furthermore, metabolic processes related to energy supply, cell function, signal transduction, and amino acid synthesis are disturbed by shell damage and/or acute acidification, indicating that both shell damage and acute acidification increased energy consumption, and disturb phospholipid synthesis, osmotic regulation, and redox balance. Free amino acid analysis and enzymatic activity assays partially confirmed our findings, highlighting the adaptation of M. coruscus to dramatic pH fluctuations in the Yangtze River estuary., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2023 Fan et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

The hard-shell mussel ( Mytilus coruscus ) is widespread in the temperate coastal areas of the northwest Pacific and holds a significant position in the shellfish aquaculture market in China. However, the natural resources of this species have been declining, and population genetic studies of M. coruscus are also lacking. In this study, we conducted whole-genome resequencing (WGR) of M. coruscus from eight different latitudes along the Chinese coast and identified a total of 25,859,986 single nucleotide polymorphism (SNP) markers. Our findings indicated that the genetic diversity of M. coruscus from the Zhoushan region was lower compared with populations from other regions. Furthermore, we observed that the evolutionary tree clustered into two primary branches, and the Zhangzhou (ZZ) population was in a separate branch. The ZZ population was partly isolated from populations in other regions, but the distribution of branches was not geographically homogeneous, and a nested pattern emerged, consistent with the population differentiation index ( F ST ) results. To investigate the selection characteristics, we utilized the northern M. coruscus populations (Dalian and Qingdao) and the central populations (Zhoushan and Xiangshan) as reference populations and the southern ZZ population as the target population. Our selection scan analysis identified several genes associated with thermal responses, including Hsp70 and CYP450 . These genes may play important roles in the adaptation of M. coruscus to different living environments. Overall, our study provides a comprehensive understanding of the genomic diversity of coastal M. coruscus in China and is a valuable resource for future studies on genetic breeding and the evolutionary adaptation of this species.

Toll-like receptors (TLRs) are crucial players in immune recognition and regulation, with aberrant activation leading to autoimmune, chronic inflammatory, and infectious diseases. MicroRNAs (miRNAs) have been shown to regulate gene expression at transcriptional and post-transcriptional levels. While miRNA-mediated regulation of TLR signaling has been studied in mammals, the underlying mechanisms of TLR-miRNA interactions in molluscs remain unclear. In a previous study, one of the TLR genes potentially targeted by miRNAs was identified and named McTLR-like1. McTLR-like1 was later found to be targeted by miRNA Mc-novel&#95;miR&#95;196 through bioinformatic prediction. In this study, we aim to experimentally determine the interaction between McTLR-like1 and Mc-novel&#95;miR&#95;196, as well as their functional role in the innate immune response of molluscs. The results showed that the expression of Mc-novel&#95;miR&#95;196 was suppressed, while the expression of McTLR-like1 was enhanced in M. coruscus hemocytes treated with lipopolysaccharide (LPS). Moreover, in vitro assays demonstrated that Mc-novel&#95;miR&#95;196 directly targets the 5' UTR of McTLR-like1 and leads to the down-regulation of proinflammatory cytokines in hemocytes. In addition, co-transfection experiments confirmed that Mc-novel&#95;miR&#95;196 inhibits McTLR-like1 and inhibits the expression of proinflammatory cytokines. The Tunel assay also showed that Mc-novel&#95;miR&#95;196 inhibited apoptosis in hemocytes induced by LPS. Our findings suggest that microRNA Mc-novel&#95;miR&#95;196 acts as a regulator of innate immunity in M. coruscus by targeting McTLR-like1 and inhibiting inflammatory response and apoptosis. These results provide further insights into the complex molecular mechanisms underlying TLR signaling in molluscs., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Interleukin-17 (IL-17) represents a class of proinflammatory cytokines involved in chronic inflammatory and degenerative disorders. Prior to this study, it was predicted that an IL-17 homolog could be targeted by Mc -novel&#95;miR&#95;145 to participate in the immune response of Mytilus coruscus . This study employed a variety of molecular and cell biology research methods to explore the association between Mc -novel&#95;miR&#95;145 and IL-17 homolog and their immunomodulatory effects. The bioinformatics prediction confirmed the affiliation of the IL-17 homolog with the mussel IL-17 family, followed by quantitative real-time PCR assays (qPCR) to demonstrate that Mc IL-17-3 was highly expressed in immune-associated tissues and responded to bacterial challenges. Results from luciferase reporter assays confirmed the potential of Mc IL-17-3 to activate downstream NF-κb and its targeting by Mc -novel&#95;miR&#95;145 in HEK293 cells. The study also produced Mc IL-17-3 antiserum and found that Mc -novel&#95;miR&#95;145 negatively regulates Mc IL-17-3 via western blotting and qPCR assays. Furthermore, flow cytometry analysis indicated that Mc -novel&#95;miR&#95;145 negatively regulated Mc IL-17-3 to alleviate LPS-induced apoptosis. Collectively, the current results showed that Mc IL-17-3 played an important role in molluscan immune defense against bacterial attack. Furthermore, Mc IL-17-3 was negatively regulated by Mc -novel&#95;miR&#95;145 to participate in LPS-induced apoptosis. Our findings provide new insights into noncoding RNA regulation in invertebrate models.

Research to assess the impacts of mariculture on the microbiota of the surrounding environment is still inadequate. Here, we examined the effects of Mytilus coruscus farming on the diversity of bacterial community in surrounding seawater using field investigations and indoor simulations, focusing on the variation of members of aerobic anoxygenic photoheterotrophic (AAP) bacteria. In the field, Mytilus farming shaped bacterial community and significantly increased their diversity, including biomass, OTUs, Shannon, relative abundance, number of enriched species, as compared with the non-farming area. Higher abundance of AAP related genera was observed in the Mytilus farming seawater. Under the controlled condition, the presence of M. coruscus significantly shaped the bacterial community composition and caused species composition to become similar after 10 days. Furthermore, the presence of M. coruscus consistently strengthened local diversity in seawater bacterial community, with linkages to the recruitment of AAP members as well. In addition, the tissue-related composition of M. coruscus significantly differed from those in seawater. Our findings highlight a ecological importance of Mytilus farming, as process that shape surrounding water-cultured bacterial community and offer experimental evidence for the accumulation of AAP-related genera in aquaculture systems., Competing Interests: Declaration of competing interest The Authors have declared that no competing interests., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Plastic pollution represents one of the most severe marine environmental issues today. In the present study, mussel Mytilus coruscus, was selected as the model organism to probe the toxic effects of acute exposure to different sizes of plastic particles using integrated transcriptomic techniques and histological and biochemical analysis. Nanoplastics (NPs) were efficiently ingested by mussels, thereby inducing a severe inflammatory response. Although no distinct aggregation of microplastics (MPs) was observed, a slight inflammatory response has still occurred. Biochemical analysis revealed a significant up-regulation of biomarkers after exposure to plastic particles. Further, NPs caused more ROS production and higher T-AOC level than MPs. Transcriptomic sequencing was performed, and these differentially expressed genes after MNPs exposure were mostly enriched in pathways involved in stress and immune response. Notably, a contrast expression, substantial upregulation in MPs treatment and downregulation in NPs treatment of specific genes include in these pathways were revealed. Collectively, these results indicated that acute exposure to NPs is more toxic than MPs. Additionally, MPs exposure perhaps caused the impairment of olfactory function and neurotoxicity to mussels. These data provided some new clues for the elucidating of ecotoxicological mechanisms underlying plastic particles exposure., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Mytilus shows great immune resistance to various bacteria from the living waters, indicating a complex immune recognition mechanism against various microbes. Peptidoglycan recognition proteins (PGRPs) play an important role in the defense against invading microbes via the recognition of the immunogenic substance peptidoglycan (PGN). Therefore, eight PGRPs were identified from the gill transcriptome of Mytilus coruscus. The sequence features, expression pattern in various organs and larval development stages, and microbes induced expression profiles of these Mytilus PGRPs were determined. Our data revealed the constitutive expression of PGRPs in various organs with relative higher expression level in immune-related organs. The expression of PGRPs is developmentally regulated, and most PGRPs are undetectable in larvae stages. The expression level of most PGRPs was significantly increased with in vivo microbial challenges, showing strong response to Gram-positive strain in gill and digestive gland, strong response to Gram-negative strain in hemocytes, and relative weaker response to fungus in the three tested organs. In addition, the function analysis of the representative recombinant expressed PGRP (rMcPGRP-2) confirmed the antimicrobial and agglutination activities, showing the immune-related importance of PGRP in Mytilus. Our work suggests that Mytilus PGRPs can act as pattern recognition receptors to recognize the invading microorganisms and the antimicrobial effectors during the innate immune response of Mytilus., Competing Interests: Declaration of competing interest The authors have declared that no conflict of interests exist., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

In this study, seven transcripts representing a novel antimicrobial peptide (AMP) family with structural features similar to those of arthropod defensins were identified from Mytilus coruscus. These novel defensins from the Mytilus AMP family were named myticofensins. To explore the possible immune-related functions of these myticofensins, we examined their expression profiles in different tissues and larval stages, as well as in three immune-related tissues under the threat of different microbes. Our data revealed that the seven myticofensins had relatively high expression levels in immune-related tissues. Most myticofensins were undetectable, or had low expression levels, in different larval mussel stages. Additionally, in vivo microbial challenges significantly increased the expression levels of myticofensins in M. coruscus hemocytes, gills, and digestive glands, showing different immune response patterns under challenges from different microbes. Our data indicates that different myticofensins may have different immune functions in different tissues. Furthermore, peptide sequences corresponding to the beta-hairpin, alpha-helix, and N-terminal loop of myticofensin were synthesized and the antimicrobial activities of these peptide fragments were tested. Our data confirms the diversity of defensins in Mytilus and reports the complex regulation of these defensins in the mussel immune response to different microbes in immune-related tissues. The immune system of Mytilus has been studied for years as they are a species with strong environmental adaptations. Our data can be regarded as a step forward in the study of the adaptation of Mytilus spp. to an evolving microbial world., Competing Interests: Declaration of competing interest The authors have declared that no conflict of interests exist., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Toll-like receptors (TLRs) mediated signaling plays a vital role in activating innate and adaptive immunity. Although TLR mediated signaling has been comprehensively investigated in mammalian species, the mechanisms underlying TLR signaling in molluscs remain obscure. In the present study, a novel TLR isoform namely McTLR-like1 was identified in the thick shell mussel Mytilus coruscus. McTLR-like1 was highly expressed in molluscan immune-related tissues, and its transcriptional levels in hemocytes were significantly increased when challenged by V. alginolyticus. McTLR-like1 activated nuclear factor κB (NF-κB) and strengthened the transcription and phosphorylation of NF-κB subunit P65 in mammalian cells. Upon the silencing of McTLR-like1, the mRNA expression levels of pro-inflammatory cytokines were down-regulated, and the animals exhibited higher levels of resistance when challenged with V. alginolyticus. McMyD88a mRNA expression was also downregulated alongside McTLR-like1. Furthermore, GST-pull down assays revealed a visible affinity between McTLR-like1 and McMyD88a. Collectively, these results demonstrated that the newly identified gene affiliated to the molluscan TLR family and plays a role in the TLR-mediated activation of inflammatory response via its affinity with MyD88. The present study enhances our knowledge of TLR signaling mechanisms in molluscs and provides new insights into the evolution of TLRs., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The thick shell mussel Mytilus coruscus has developed into a model species for studying the interaction between molluscs and environmental stimuli. Herein, integrated analysis of miRNAome and transcriptome was performed to reveal miRNA-mRNA network regulation in Vibrio alginolyticus infected M. coruscus. There have detected some histological abnormalities in digestive gland and gills of V. alginolyticus challenged mussels, ascertaining the effective irritation by the present bacterial strain. A total of 265 novel miRNAs were finally predicted, of which 26 were differentially expressed miRNAs (DEMs). Additionally, 667 differentially expressed genes (DEGs) were detected, which may be potentially associated with innate immune response to V. alginolyticus infection. A regulatory network linked to 22 important pathways and 16 DEMs and 34 OGs was constructed. Some traditional immune-related signaling pathways such as toll-like receptor signaling pathway (TLR) signaling pathway, transforming growth factor-beta (TGF-beta) signaling pathway, peroxisome, phagosome, lysosome, mammalian target of rapamyoin (mTOR) signaling pathway were linked to specific miRNAs and genes in this network. Further, interactional relationship between certain miRNAs and TLR pathway was dissected, which the results predicted that a number of TLRs and TLR-associated signaling genes including TLR1, TLR2, TLR4, TLR6, IRAK1, TRAF6, MAPK, and IL-17 were negatively regulated by novel&#95;miR&#95;11, novel&#95;miR&#95;145, novel&#95;miR&#95;196, novel&#95;miR&#95;5, novel&#95;miR&#95;163 and novel&#95;miR&#95;217 in the TLR pathway. Additionally, interactional relationship between novel&#95;miR&#95;145 and TLR2 was validated by laboratory experiment. The integrated analysis of mRNA and microRNA deep sequencing data exhibited a sophisticated miRNA-mRNA regulation network in M. coruscus in response to V. alginolyticus challenge, which shed a new light on the underlying mechanism of molluscan confronting bacterial infection., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

CYP3A enzymes play a crucial role in metabolic clearance of a variety of xenobiotics. However, their genetic information and function remain unclear in molluscs. In the present study, two novel CYP3A genes i.e. McCYP3A-1 and McCYP3A-2 were identified and characterized from the thick shell mussel Mytilus coruscus, and their tissue distribution as well as the response to cadmium (Cd) and benzo[a]pyrene (B[α]P) exposure were addressed using real time quantitative RT-PCR (qRT-PCR) and erythromycin N-demethylase (ERND) assay. McCYP3A-1 and McCYP3A-2 possess typically domains of CYP family such as helix-C, helix-I, helix-K, PERF and the heme binding domain as well as the characteristic domains of CYP3s including six SRS motifs. McCYP3A-1 and McCYP3A-2 transcripts were constitutively expressed in all examined tissues with high expression level in digestive glands, hepatopancreas and gonads. Upon B[α]P exposure, McCYP3A-1 and McCYP3A-2 mRNA expression in digestive glands showed a pattern of up-regulation followed by down-regulation, while under Cd exposure, showed a time-dependent induction profile. In addition, ERND activity, generally used as an indicator of CYP3, increased in a time-dependent manner after exposure to Cd and B[α]P. These results collectively indicated that McCYP3A-1 and McCYP3A-2 are CYP3A family member and may play a potential role in metabolic clearance of xenobiotics. Meanwhile, the current results may provide some baseline data to support McCYP3A-1 and McCYP3A-2 as candidate biomarkers for monitoring of PAHs and heavy metal pollution., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Carnosine and its analogues are histidine-containing dipeptides (HCDs) playing diverse functions in vertebrates. However, the distribution and the metabolism of carnosine in invertebrates are still unknown. In this study, Mytilus coruscus, a shellfish with important economic value in China, was selected for the investigation of HCD content and the expression profiling of carnosine-related genes in various mussel tissues. Quantification of HCD by amino acids analyzer revealed a low concentration of anserine in muscular tissues in Mytilus, indicating the presence of HCD even in an invertebrate. mRNA expression of five carnosine metabolic-related genes was profiled in various tissues, and the results highlighted the relative higher expression level of these genes in muscular tissues. Considering the fact that beta-alanine supplementation can increase the HCD content in vertebrates, a beta-alanine injection was performed and the changes of HCD concentration and the mRNA expression of carnosine related genes were investigated in five mussel tissues. The results revealed the increase of HCD concentration, as well as the up-regulated expression level of related genes, in tested tissues of beta-alanine injected mussels. Transcriptomic analysis for the whole soft tissue of mussel before and after beta-alanine injection were performed, and 3 569 differential expression genes (DEGs) were identified in the beta-alanine injected group when compared to their expression levels in the control. These data indicated the complex effects of beta-alanine on M. coruscus metabolism, and those DEGs enriched in pathways of cancers, muscle contraction, and tyrosine metabolism highlighted the possible functions of beta-alanine in cell proliferation, sports, and melanogenesis, respectively. [ABSTRACT FROM AUTHOR]

Mollusk shells are products of biomineralization and possess excellent mechanical properties, and shell matrix proteins (SMPs) have important functions in shell formation. A novel SMP with a PDZ domain (PDZ-domain-containing-protein-1, PDCP-1) was identified from the shell matrices of Mytilus coruscus. In this study, the gene expression, function, and location of PDCP-1 were analyzed. PDCP-1 was characterized as an ∼70 kDa protein with a PDZ (postsynaptic density/discs large/zonula occludes) domain and a ZM (ZASP-like motif) domain. The PDCP-1 gene has a high expression level and specific location in the foot, mantle and adductor muscle. Recombinantly expressed PDCP-1 (rPDCP-1) altered the morphology of calcite crystals, the polymorph of calcite crystals, binding with both calcite and aragonite crystals, and inhibition of the crystallization rate of calcite crystals. In addition, anti-rPDCP-1 antibody was prepared, and immunohistochemistry and immunofluorescence analyses revealed the specific location of PDCP-1 in the mantle, the adductor muscle, and the aragonite (nacre and myostracum) layer of the shell, suggesting multiple functions of PDCP-1 in biomineralization, muscle-shell attachment, and muscle attraction. Furthermore, pull-down analysis revealed 19 protein partners of PDCP-1 from the shell matrices, which accordingly provided a possible interaction network of PDCP-1 in the shell. These results expand the understanding of the functions of PDZ-domain-containing proteins (PDCPs) in biomineralization and the supramolecular chemistry that contributes to shell formation. [ABSTRACT FROM AUTHOR]

• Hox genes in Mytilus coruscus at the genome level were used to speculated the formation of subcluster collinearity in gene structure, synteny and evolution analysis. • The Hox gene expression profile in larval stages suggests the existence of subcluster collinearity in M. coruscus. • The clustering of Hox sequences in M. coruscus was different with the clustering between species. • Hox genes in bivalves provided the basis for the expression patterns of four Hox subclusters. Hox genes encode transcription factors that are crucial regulators of various developmental processes, including patterning of the body axis and differentiation of cells, tissues and organs. They are organized in clusters in a wide range of Metazoans and expressed during embryonic development in a collinear manner from the 3′ to the 5′ end of these genomic units. Hox genes are part of the larger homeobox gene super-class, and other gene clusters beyond Hox are being increasingly discovered. This transcriptional dynamic generates spatiotemporal expression patterns throughout the developing body that are required for the establishment of fields of cell identity. Here we suggest that subcluster temporal collinearity may occur during the development of a bivalve species, as demonstrated for other Bilateran species. We performed a genome-wide analysis of the Mytilus coruscus Hox gene family, including gene structure, synteny, and expression patterns. It was shown that 11 Hox genes were evenly distributed within one chromosome in M. coruscus. Phylogenetic analysis showed that 11 Hox proteins were divided into four groups and each of them contained different conserved motifs. Besides, sequence alignment and analysis showed the conservation of 11 Hox genes of M. coruscus. Selection pressure analysis revealed the Ka/Ks ratios of Hox1 , Hox4 , Lox4 , Post2 , and Post1 were less than 1 in Bivalvia, indicating that these five Hox genes suffered significant purifying selection. Notably, Hox1 , Hox4 , Post2 were overlapped with the leading gene in the subcluster collinearity. This discovery suggests the potential existence of subcluster temporal collinearity in M. coruscus , which adds new insights into Hox gene organization in Bivalvia or Mollusca. [ABSTRACT FROM AUTHOR]

Aquatic animals, such as the marine mussel, Mytilus coruscus , are regularly subjected to starvation due to conditions of food scarcity brought about by environmental change. Silent mating type information regulation 2 homolog 1 (sirt1) is triggered during animal starvation and participates in inflammation and stress responses. However, the function of sirt1 in Mytilus remains unknown; thus, exploring the effects of sirt1 will improve the understanding of the resistance of Mytilus to starvation. In this study, Mytilus coruscus were fasted for 9 days and treated with 20 μM resveratrol. The results indicated that sitr1 mRNA expression levels in the gonads and gills of mussels increased significantly after 3 days of starvation and significantly decreased after 9 days of starvation. 20 μM resveratrol significantly up-regulated sirt1 expression in the gonads and gills of mussels starved for 9 days. The condition factor and gonadal index considerably decreased in mussels under starvation stress. The activities of antioxidants SOD, CAT, GSH, GPX, and AKP were elevated after fasting for 3 days, but were reduced after starvation for 9 days, accompanied by histopathological damage in the gills and gonads. Resveratrol alleviates histological damage caused by starvation stress by enhancing antioxidant activity and reducing MDA production. Additionally, resveratrol decreased the mRNA expression levels of tlr4 , myd88 , and nfkb and increased the mRNA expression levels of ampk , foxo , and gadd45. Overall, the results suggest that resveratrol-induced sirt1 expression exerts a protective effect on mussels risking starvation by regulating TLR4/NFκB and AMPK/FOXO signaling pathways. This study might give us fresh insight into the effects of sirt1 on the response to starvation stress in mussels. • Starvation stress induces a temporary increase in the antioxidant capacity in mussels. • Prolonged starvation stress induced oxidative damage in mussels. • Resveratrol alleviates starvation stress induced histological damage via enhancing the antioxidant ability of mussels. • Resveratrol protects starvation stressed mussels by regulating sirt1 -mediated TLR4/NFκB and AMPK/FOXO signaling pathways. [ABSTRACT FROM AUTHOR]

Antimicrobial peptides (AMPs) play a fundamental role in mussels' innate immunity, preventing the invasion of potential pathogens. Previous research has shown that AMPs are abundant in Mytilus species. A mussel with important economic value and limited distribution in the East China Sea, M. coruscus , also contains abundant AMPs, including the mytichitin and myticusin identified previously in this species. However, the molecular diversity and expression pattern of M. coruscus AMPs remain largely unknown. Based on the dataset of the M. coruscus hemocyte transcriptome, we identified twelve AMPs representing the main AMP families present in M. coruscus , including three novel AMPs (two arthropod-like and one crustin-like). The variations in the expression of the genes encoding these AMPs have been analyzed in different tissues, different larval development stages, and different M. coruscus individuals, as well as in hemocytes and gonads under the threat of different microbes. The results suggest that in adult M. coruscus , the gonads and hemocytes are the sources of AMPs for mussels collected in winter and summer, respectively. The expression of AMPs is developmentally regulated, and most AMPs are undetectable in larvae until after larval settlement and metamorphosis. In vivo microbial challenges significantly increased the expression of AMPs in M. coruscus hemocytes, and different AMP response patterns under challenges from different microbes were observed, showing a rapid, strong response to gram-positive strains, a weak response to gram-negative strains, and a long-term response to fungus. While the gonads showed a different response pattern than the hemocytes, with stronger changes in expression relative to the control and stronger fluctuation in the expression level of some AMPs. Finally, LC-MS/MS was used for peptidomic analysis of the AMPs in M. coruscus , and the results confirmed the presence of several AMP families in the mussel serum • The diversity of the antimicrobial peptide families was explored in M. coruscus. • The expression level of these AMPs have been analyzed in different mussel tissues. • Our data revealed the developmentally regulation of AMPs expression in mussel larvae. • Different responses of these AMPs under different microbes challenge were observed. • Peptidomic analysis was performed for identification of AMPs in mussel serum. [ABSTRACT FROM AUTHOR]

Mytilus can survive in heavily anthropized coastal waters despite being constantly surrounded by abundant microorganisms, indicating an environmental adaptation and therefore an important research significance for this species. However, there is a qualitative and quantitative lack of knowledge of the molecular mechanisms involved in the physiology and immune response of Mytilus tissues, especially in tissues other than hemocytes. For filling this gap, we have studied the transcriptome of gill and gonad of M. coruscus exposed to distinct stimuli, including antibiotics pretreatment and subsequent different bacteria challenges at two time points. A total of 36 cDNA libraries were sequenced and 245.01 Gb clean data was acquired with an average of 5.91 GB and Q30 > 94% for each library. The filtered high-quality reads were assembled into 91,850 transcripts, which after clustering resulted in 59,206 unigenes. Overall, 19,783 differentially expressed genes (DEGs) were detected from the pair-wise comparisons among the gill samples, and 12,655 DEGs among the gonad samples. Comparing with the gonad, the gill showed strong immune-related responses towards bacteria challenge, with abundant immune-related signaling pathway being disturbed, highlighting the important roles of gill in mussel immune system and the tissue specificity of mussel immune responses. The gonad showed that the DEGs induced by bacteria were mainly enriched in regulatory pathways related to cell growth and proliferation. In addition, both gill and gonad presented rapid activation towards Micrococcus luteus infection comparing with that of Vibrio parahemolyticus , indicating a more sensitivity of mussel to Gram-positive bacteria. Our data revealed different immune responses in different mussel tissues under different bacteria challenges, and thus provided clues for exploring the mechanism of mussel immune system. • The transcriptome of M. coruscus gill and gonad were analyzed under distinct stimuli. • Antibiotics pretreatment of mussel provided a clean background for bacteria challenge. • The gill showed a stronger immune response to bacteria challenge than that of gonad. • Both gill and gonad showed rapid immune responses towards Gram-positive bacterium. • Gram-negative bacterium challenge induced the immune response with fall-rise pattern. [ABSTRACT FROM AUTHOR]