Cloning and expression analysis of the gene encoding fibrinogen-like protein A, a novel regeneration-related protein from Apostichopus japonicus

Identification of Key Genes Correlated with Economic Trait Superiorities and Their SNP Screening Through Transcriptome Comparisons, WGCNA and Pearson Correlation Coefficient in the Sea Cucumber Apostichopus Japonicus

Variation in morphology-driven economic traits is a common issue hindering the development of the sea cucumber aquaculture industry. In this study, transcriptome comparisons, weighted gene correlation network analysis (WGCNA) and Pearson correlation coefficient (PCC) were first employed to identify key genes correlated with morphological variation in the sea cucumber Apostichopus japonicus, after which the relationship between identified key genes (relative expression and genotype) and economic trait phenotypes was investigated to screen potential biomarker targets for molecular-assisted breeding. The results showed that three genes (putative ficolin-2, fibrinogen c domain-containing protein 1, and angiopoietin-4) were closely associated with economic trait superiorities. Two single nucleotide polymorphisms (SNPs) were identified in the putative ficolin-2 gene as having a strong correlation with body weight and papilla number. The findings from this study will enrich breeding biomarker resources and benefit the development of molecular-assisted breeding techniques in sea cucumber aquaculture.

TMT-based proteomics analysis of growth advantage of triploid Apostichopus japonicus

Polyploid breeding can produce new species with a faster growth rate, higher disease resistance, and higher survival rate, and has achieved significant economic benefits. This study investigated the protein differences in the body wall of triploid Apostichopus japonicus and diploid A. japonicus using isotope-labeled relative and absolute quantitative Tandem Mass Tag technology. A total of 21,096 independent peptides and 4621 proteins were identified. Among them, there were 723 proteins with significant expression differences, including 413 up-regulated proteins and 310 down-regulated proteins. The differentially expressed proteins (DEPs) were enriched in 4519 Gene Ontology enrichment pathways and 320 Kyoto Encyclopedia of Genes and Genomes enrichment pathways. Twenty-two key DEPs related to important functions such as growth and immunity of triploid A. japonicus were screened from the results, among which 20 were up-regulated, such as cathepsin L2 cysteine protease and fibrinogen-like protein A. Arylsulfatase A and zonadhesin were down-regulated. The up-regulated proteins were mainly involved in oxidative stress response, innate immune response, and collagen synthesis in triploid A. japonicus, and the down-regulated proteins were mainly associated with the sterility of triploid A. japonicus. In addition, the transcriptome and proteome were analyzed jointly to support proteome data. In this study, the differences in protein composition between triploid and diploid A. japonicus were analyzed for the first time, and the results revealed the underlying reasons for the growth advantage of triploid A. japonicus.

CircRNA75 and CircRNA72 Function as the Sponge of MicroRNA-200 to Suppress Coelomocyte Apoptosis Via Targeting Tollip in Apostichopus japonicus

Circular RNAs (circRNAs) act as essential regulators in many biological processes, especially in mammalian immune response. Nonetheless, the functions and mechanisms of circRNAs in the invertebrate immune system are largely unclarified. In our previous work, 261 differentially expressed circRNAs potentially related to the development of Apostichopus japonicus skin ulceration syndrome (SUS), which is a major problem restricting the sea cucumber breeding industry, were identified by genome-wide screening. In this study, via miRanda analysis, both circRNA75 and circrRNA72 were shown to share the miR-200 binding site, a key microRNA in the SUS. The two circRNAs were verified to be increased significantly in LPS-exposed primary coelomocytes, similar to the results of circRNA-seq in sea cucumber under Vibrio splendidus-challenged conditions. A dual-luciferase assay indicated that both circRNA75 and circRNA72 could bind miR-200 in vivo, in which circRNA75 had four binding sites of miR-200 and only one for circRNA72. Furthermore, we found that miR-200 could bind the 3’-UTR of Toll interacting protein (Tollip) to negatively mediate the expression of Tollip. Silencing Tollip increased primary coelomocyte apoptosis. Consistently, inference of circRNA75 and circRNA72 could also downregulate Tollip expression, thereby increasing the apoptosis of primary coelomocytes, which could be blocked by miR-200 inhibitor treatment. Moreover, the rate of si-circRNA75-downregulated Tollip expression was higher than that of si-circRNA72 under an equivalent amount. CircRNA75 and circRNA72 suppressed coelomocyte apoptosis by sponging miR-200 to promote Tollip expression. The ability of circRNA to adsorb miRNA might be positively related to the number of binding sites for miRNA.

RNA Sequencing Analysis to Capture the Transcriptome Landscape during Tenderization in Sea Cucumber Apostichopus japonicus

Sea cucumber (Apostichopus japonicus) is an economically significant species in China having great commercial value. It is challenging to maintain the textural properties during thermal processing due to the distinctive physiochemical structure of the A. japonicus body wall (AJBW). In this study, the gene expression profiles associated with tenderization in AJBW were determined at 0 h (CON), 1 h (T_1h), and 3 h (T_3h) after treatment at 37 °C using Illumina HiSeq™ 4000 platform. Seven-hundred-and-twenty-one and 806 differentially expressed genes (DEGs) were identified in comparisons of T_1h vs. CON and T_3h vs. CON, respectively. Among these DEGs, we found that two endogenous proteases-72 kDa type IV collagenase and matrix metalloproteinase 16 precursor-were significantly upregulated that could directly affect the tenderness of AJBW. In addition, 92 genes controlled four types of physiological and biochemical processes such as oxidative stress response (3), immune system process (55), apoptosis (4), and reorganization of the cytoskeleton and extracellular matrix (30). Further, the RT-qPCR results confirmed the accuracy of RNA-sequencing analysis. Our results showed the dynamic changes in global gene expression during tenderization and provided a series of candidate genes that contributed to tenderization in AJBW. This can help further studies on the genetics/molecular mechanisms associated with tenderization.

Extracellular matrix remodeling and matrix metalloproteinases (ajMMP-2 like and ajMMP-16 like) characterization during intestine regeneration of sea cucumber Apostichopus japonicus

Remodeling of extracellular matrix (ECM) regulated by matrix metalloproteinases (MMPs) is essential for tissue regeneration. In the present study, we used immunohistochemistry (IHC) techniques against ECM components to reveal changes of ECM during intestine regeneration of Apostichopus japonicus. The expression of collagen I and laminin reduced apparently from the eviscerated intestine, while fibronectin exhibited continuous expression in all regeneration stages observed. Meanwhile, we cloned two MMP genes from A. japonicus by RACE PCR. The full-length cDNA of ajMMP-2 like is 2733bp and contains a predicted open reading frame (ORF) of 1716bp encoding 572 amino acids. The full-length cDNA of ajMMP-16 like is 2705bp and contains an ORF of 1452bp encoding 484 amino acids. The predicted protein sequences of each MMP contain two conserved domains, ZnMc_MMP and HX. Homology and phylogenetic analysis revealed that ajMMP-2 like and ajMMP-16 like share high sequence similarity with MMP-2 and MMP-16 from Strongylocentrotus purpuratus, respectively. Then we investigated spatio-temporal expression of ajMMP-2 like and ajMMP-16 like during different regeneration stages by qRT-PCR and IHC. The expression pattern of them showed a roughly opposite trend from that of ECM components. According to our results, a fibronectin-dominate temporary matrix is created in intestine regeneration, and it might provide structural integrity for matrix and promote cell movement. We also hypothesize that ajMMP-2 like and ajMMP-16 like could accelerate cell migration and regulate interaction between ECM components and growth factors. This work provides new evidence of ECM and MMPs involvement in sea cucumber regeneration.

Comparative transcriptome analysis of papilla and skin in the sea cucumber, Apostichopus japonicus

Papilla and skin are two important organs of the sea cucumber. Both tissues have ectodermic origin, but they are morphologically and functionally very different. In the present study, we performed comparative transcriptome analysis of the papilla and skin from the sea cucumber (Apostichopus japonicus) in order to identify and characterize gene expression profiles by using RNA-Seq technology. We generated 30.6 and 36.4 million clean reads from the papilla and skin and de novo assembled in 156,501 transcripts. The Gene Ontology (GO) analysis indicated that cell part, metabolic process and catalytic activity were the most abundant GO category in cell component, biological process and molecular funcation, respectively. Comparative transcriptome analysis between the papilla and skin allowed the identification of 1,059 differentially expressed genes, of which 739 genes were expressed at higher levels in papilla, while 320 were expressed at higher levels in skin. In addition, 236 differentially expressed unigenes were not annotated with any database, 160 of which were apparently expressed at higher levels in papilla, 76 were expressed at higher levels in skin. We identified a total of 288 papilla-specific genes, 171 skin-specific genes and 600 co-expressed genes. Also, 40 genes in papilla-specific were not annotated with any database, 2 in skin-specific. Development-related genes were also enriched, such as fibroblast growth factor, transforming growth factor-β, collagen-α2 and Integrin-α2, which may be related to the formation of the papilla and skin in sea cucumber. Further pathway analysis identified ten KEGG pathways that were differently enriched between the papilla and skin. The findings on expression profiles between two key organs of the sea cucumber should be valuable to reveal molecular mechanisms involved in the development of organs that are related but with morphological differences in the sea cucumber.