Genome-wide DNA Methylation Analysis of Mantle Edge and Mantle Central from Pearl Oyster Pinctada fucata martensii

miR-10a-3p Participates in Nacre Formation in the Pearl Oyster Pinctada fucata martensii by Targeting NPY

MicroRNAs (miRNAs) are small noncoding RNAs that regulate gene expression via the recognition of their target messenger RNAs. MiR-10a-3p plays an important role in the process of ossification. In this study, we obtained the precursor sequence of miR-10a-3p in the pearl oyster Pinctada fucata martensii (Pm-miR-10a-3p) and verified its sequence by miR-RACE technology, and detected its expression level in the mantle tissues of the pearl oyster P. f. martensii. Pm-nAChRsα and Pm-NPY were identified as the potential target genes of Pm-miR-10a-3p. After the over-expression of Pm-miR-10a-3p, the target genes Pm-nAChRsα and Pm-NPY were downregulated, and the nacre microstructure became disordered. The Pm-miR-10a-3p mimic obviously inhibited the luciferase activity of the 3' untranslated region of the Pm-NPY gene. When the interaction site was mutated, the inhibitory effect disappeared. Our results suggested that Pm-miR-10a-3p participates in nacre formation in P. f. martensii by targeting Pm-NPY. This study can expand our understanding of the mechanism of biomineralization in pearl oysters.

Epigenetic and Genetic Population Structure is Coupled in a Marine Invertebrate

Delineating the relative influence of genotype and the environment on DNA methylation is critical for characterizing the spectrum of organism fitness as driven by adaptation and phenotypic plasticity. In this study, we integrated genomic and DNA methylation data for two distinct Olympia oyster (Ostrea lurida) populations while controlling for within-generation environmental influences. In addition to providing the first characterization of genome-wide DNA methylation patterns in the oyster genus Ostrea, we identified 3,963 differentially methylated loci between populations. Our results show a clear coupling between genetic and epigenetic patterns of variation, with 27% of variation in interindividual methylation differences explained by genotype. Underlying this association are both direct genetic changes in CpGs (CpG-SNPs) and genetic variation with indirect influence on methylation (mQTLs). When comparing measures of genetic and epigenetic population divergence at specific genomic regions this relationship surprisingly breaks down, which has implications for the methods commonly used to study epigenetic and genetic coupling in marine invertebrates.

Immunomodulatory effects of decitabine in pearl oyster Pinctada fucata martensii

Decitabine (DAC), an inhibitor of DNA methyltransferase, is typically used to reverse DNA methylation and is considered an epigenetic modifying drug. DNA methylation is crucial to the regulation of gene expression without altering genetic information. Our previous research showed that the DNA methylation levels of many immune-related genes changed after the pre-grafting condition in pearl production. In the present study, we evaluated the DNA methylation level and analyzed transcriptome, enzyme, and antimicrobial activities after DAC treatment to evaluate the effect of DAC on DNA methylation and immune system of pearl oyster Pinctada fucata martensii. Results showed that DAC significantly decreased the level of global DNA methylation in the hemocytes of the pearl oysters. Transcriptome analysis obtained 577 differentially expressed genes (DEGs) between the control and DAC treatment group. The DEGs were mainly enriched in the following pathways: "Relaxin signaling pathway," "Cytosolic DNA-sensing pathway," "Platelet activation," and "Peroxisome," and related genes were overexpressed after DAC treatment. DAC treatment resulted in a substantial increase in the levels of serum superoxide dismutase, interleukin-17, phenol oxidase, tumor necrosis factor, and antimicrobial activity, compared with the control. These results suggested that DAC can alter DNA methylation level, activate immune-related genes, and improve the level of humoral immunity in pearl oysters, thereby increasing our understanding of the mechanism underlying DNA methylation in immune regulation.

Comparative Methylome Analysis Reveals Epigenetic Signatures Associated with Growth and Shell Color in the Pacific Oyster, Crassostrea gigas

Fast growth is one of the most important breeding goals for all economic species such as the Pacific oyster (Crassostrea gigas), an aquaculture mollusk with top global production. Although the genetic basis and molecular mechanisms of growth-related traits have been widely investigated in the oyster, the role of DNA methylation involved in growth regulation remains largely unexplored. In this study, we performed a comparative DNA methylome analysis of two selectively bred C. gigas strains with contrasted phenotypes in growth and shell color based on whole-genome bisulfite sequencing (WGBS). Genome-wide profiling of DNA methylation at the single-base resolution revealed that DNA methylations were widely spread across the genome with obvious hotspots, coinciding with the distribution of genes and repetitive elements. Higher methylation levels were observed within genic regions compared with intergenic and promoter regions. Comparative analysis of DNA methylation allowed the identification of 339,604 differentially methylated CpG sites (DMCs) clustering in 27,600 differentially methylated regions (DMRs). Functional annotation analysis identified 11,033 genes from DMRs which were enriched in biological processes including cytoskeleton system, cell cycle, signal transduction, and protein biosynthesis. Integrative analysis of methylome and transcriptome profiles revealed a positive correlation between gene expression and DNA methylation within gene-body regions. Protein-protein interaction (PPI) analysis of differentially expressed and methylated genes allowed for the identification of integrin beta-6 (homolog of human ITGB3) as a hub modulator of the PI3K/Akt signaling pathway that was involved in various growth-related processes. This work provided insights into epigenetic regulation of growth in oysters and will be valuable resources for studying DNA methylation in invertebrates.

DNA Methylation Analyses Unveil a Regulatory Landscape in the Formation of Nacre Color in Pearl Oyster Pinctada fucata martensii

Pearl color is regulated by genetics, biological pigments, and organic matrices and an important factor that influences the pearl economic value. The epigenetic regulation mechanism underlying pearl pigmentation remains poorly understood. In this study, we collected the mantle pallial (MP) and mantle central (MC) of the golden-lipped strain, and MP of the silver-lipped strain of pearl oyster Pinctada fucata martensii. The whole-genome bisulfite sequencing (WGBS) technology was employed to investigate the possible implication of epigenetic factors regulating nacre color variation. Our results revealed approximately 2.5% of the cytosines in the genome of the P. fucata martensii were methylated, with the CG methylation type was in most abundance. Overall, we identified 12, 621 differentially methylated regions (DMRs) corresponding to 3,471 DMR-associated genes (DMGs) between the two comparison groups. These DMGs were principally enriched into KEGG metabolic pathways including ABC transporters, Terpenoid backbone biosynthesis, and fatty acid degradation. In addition, integrating information about DMGs, DEGs, and function annotation indicated eight genes LDLR, NinaB, RDH, CYP, FADS, fn3, PU-1, KRMP as the candidate genes related to pigmentation of nacre color. A further study proved that the pigment in nacre is violaxanthin. The results of our study provide the support that there is an association between nacre color formation and DNA methylation profiles and will help to reveal the epigenetic regulation of nacre pigmentation formation in pearl oyster P. fucata martensii.

Exploring crucial molecular events in pearl oyster after pre-grafting conditioning by genome-wide bisulfite sequencing for DNA methylation analysis

Pre-grafting condition is an important method to promote recovery from transplant surgery during pearl production. In the present study, we constructed two DNA methylomes from pearl oysters with and without conditioning to investigate the molecular mechanism of the pearl oyster Pinctada fucata martensii underlying the pre-grafting condition. A total of 4,594,997 and 4,930,813 methyl CG in the control (Con) and pre-grafting group (PT) were detected, resulting in the whole genome methylation profile and methylation pattern in P. f. martensii. Results reveal that the promoter, especially the CpG island-rich region, was more infrequently methylated than the gene function elements in P. f. martensii. A total of 51,957 differently methylated regions (DMRs) between Con and PT were obtained, including 3789 DMR in the promoter and 16,021 in the gene body. Based on gene ontology and pathway enrichment analyses, these DMRs were mainly related to "cellular process", "metabolic process", "Epstein-Barr virus infection", and "Fanconi anemia pathway". The methylation site in the promoter region may be associated with the promoter activity and transcription factor binding. These results help our understanding of the mechanism of pre-grafting condition, thereby providing key information in guiding to improve the conditioning methods for enhanced pearl oyster survival rate after transplantation.

Genome-wide DNA methylation profile changes associated with shell colouration in the Yesso scallop (Patinopecten yessoensis) as measured by whole-genome bisulfite sequencing

BACKGROUND

Mollusca, a phylum of highly rich species, possess vivid shell colours, but the underlying molecular mechanism remains to be elucidated. DNA methylation, one of the most common epigenetic modifications in eukaryotes, is believed to play a vital role in various biological processes. However, analysis of the effects of DNA methylation on shell colouration has rarely been performed in molluscs, limiting the current knowledge of the molecular mechanism of shell colour formation.

RESULTS

In the present study, to reveal the role of epigenetic regulation in shell colouration, WGBS, the "gold standard" of DNA methylation analysis, was first performed on the mantle tissues of Yesso scallops (Patinopecten yessoensis) with different shell colours (brown and white), and DNA methylomes at single-base resolution were generated. About 3% of cytosines were methylated in the genome of the Yesso scallop. A slight increase in ^mCG percentage and methylation level was found in brown scallops. Sequence preference of nearby methylated cytosines differed between high and low methylation level sites and between the brown- and white-shelled scallops. DNA methylation levels varied among the different genomic regions; all the detected regions in the brown group exhibited higher methylation levels than the white group. A total of 41,175 DMRs (differentially methylated regions) were detected between brown and white scallops. GO functions and pathways associated with the biosynthesis of melanin and porphyrins were significantly enriched for DMRs, among which several key shell colour-related genes were identified. Further, different correlations between mRNA expression levels and DNA methylation status were found in these genes, suggesting that DNA methylation regulates shell colouration in the Yesso scallop.

CONCLUSIONS

This study provides genome-wide DNA methylation landscapes of Yesso scallops with different shell colours, offering new insights into the epigenetic regulatory mechanism underlying shell colour.

Oyster biomineralization under ocean acidification: From genes to shell

Biomineralization is one of the key processes that is notably affected in marine calcifiers such as oysters under ocean acidification (OA). Understanding molecular changes in the biomineralization process under OA and its heritability, therefore, is key to developing conservation strategies for protecting ecologically and economically important oyster species. To do this, in this study, we have explicitly chosen the tissue involved in biomineralization (mantle) of an estuarine commercial oyster species, Crassostrea hongkongensis. The primary aim of this study is to understand the influence of DNA methylation over gene expression of mantle tissue under decreased ~pH 7.4, a proxy of OA, and to extrapolate if these molecular changes can be observed in the product of biomineralization-the shell. We grew early juvenile C. hongkongensis, under decreased ~pH 7.4 and control ~pH 8.0 over 4.5 months and studied OA-induced DNA methylation and gene expression patterns along with shell properties such as microstructure, crystal orientation and hardness. The population of oysters used in this study was found to be moderately resilient to OA at the end of the experiment. The expression of key biomineralization-related genes such as carbonic anhydrase and alkaline phosphatase remained unaffected; thus, the mechanical properties of the shell (shell growth rate, hardness and crystal orientation) were also maintained without any significant difference between control and OA conditions with signs of severe dissolution. In addition, this study makes three major conclusions: (1) higher expression of Ca²⁺ binding/signalling-related genes in the mantle plays a key role in maintaining biomineralization under OA; (2) DNA methylation changes occur in response to OA; however, these methylation changes do not directly control gene expression; and (3) OA would be more of a 'dissolution problem' rather than a 'biomineralization problem' for resilient species that maintain calcification rate with normal shell growth and mechanical properties.

Differences in DNA methylation between slow and fast muscle in Takifugu rubripes

Fish skeletal muscle is comprised of fast muscle (FM) and slow muscle (SM), which constitutes 60% of total the body mass. Fish skeletal muscle can affect fish swimming activity, which is important for aquaculture due to its growth-potentiating effects. DNA methylation can influence gene expression level. We previously identified multiple differentially expressed genes (DEGs) between FM and SM in Takifugu rubripes. However, it is unknown if the expression levels of these DEGs are influenced by DNA methylation. In the present study, we used DNA methylation sequencing to study the DNA methylation profiles of FM and SM in T. rubripes. SM had higher overall methylation levels than FM. A total of 8479 differentially methylated genes (DMGs) and 3407 DMGs containing differentially methylated regions (DMRs) in the promoter regions between FM and SM were identified. After enrichment analysis, we found functionally relevant DMGs between FM and SM, including Kapca, Plcd3a, Plcd1, Pi3k, Tsp4b and Pgfrb in the hedgehog signaling pathway and phosphatidylinositol (PI)-related pathways. Due to the different methylation levels of these genes between FM and SM, the expression levels of Kapca, Plcd3a, Plcd1, Pi3k, and Tsp4b were higher in FM and Pgfrb was higher in SM. There were differences in the hedgehog signaling pathway and PI-related pathways between FM and SM. In SM, the cytokine-cytokine receptor interaction promoted focal adhesion, while ECM-receptor interactions promoted focal adhesion in FM. These results provide information regarding the difference between FM and SM in T. rubripes.

LSD1-mediated stabilization of SEPT6 protein activates the TGF-β1 pathway and regulates non-small-cell lung cancer metastasis

Non-small cell lung cancer (NSCLC) is a prevalent cancer with unfavorable prognosis. Over the past decade accumulating studies have reported an involvement of lysine-specific histone demethylase 1 (LSD1) in NSCLC development. Here, we aimed to explore whether LSD1 affects the metastasis of NSCLC by mediating Septin 6 (SEPT6) through the TGF-β1 pathway. RT-qPCR was used to determine LSD1 and SEPT6 expression in NSCLC tissues and cells. Interactions between LSD1, SEPT6, and TGF-β1 were detected using lentivirus-mediated silencing of LSD1 and overexpression of SEPT6. The role of LSD1 and SEPT6 in mediating the biological behavior of NSCLC cells was determined using the EdU proliferation assay, Transwell assay, and flow cytometry. Thereafter, transplanted cell tumors into nude mice were used to explore the in vivo effects of LSD1 and SEPT6 on metastasis of NSCLC. LSD1 and SEPT6 were overexpressed in NSCLC tissue and cell samples. LSD1 could demethylate the promoter of the SEPT6 to positively regulate SEPT6 expression. LSD1 promoted proliferation, migration, and invasion, while suppressing the apoptosis of NSCLC cells by increasing SEPT6 expression. LSD1-mediated SEPT6 accelerated in vivo NSCLC metastasis through the TGF-β1/Smad pathway. Collectively, LSD1 demethylates SEPT6 promoter to upregulate SEPT6, which activates TGF-β1 pathway, thereby promoting metastasis of NSCLC.