A novel fucolectin from Apostichopus japonicus with broad PAMP recognition pattern

Combining a transcriptomic approach and a targeted metabolomics approach for deciphering the molecular bases of compatibility phenotype in the snail Biomphalaria glabrata toward Schistosoma mansoni

Biomphalaria glabrata is a freshwater snail and the obligatory intermediate host of Schistosoma mansoni parasite, the etiologic agent of intestinal Schistosomiasis, in South America and Caribbean. Interestingly in such host-parasite interactions, compatibility varies between populations, strains or individuals. This observed compatibility polymorphism is based on a complex molecular-matching-phenotype, the molecular bases of which have been investigated in numerous studies, notably by comparing between different strains or geographical isolates or clonal selected snail lines. Herein we propose to decipher the constitutive molecular support of this interaction in selected non-clonal resistant and susceptible snail strain originating from the same natural population from Brazil and thus having the same genetic background. Thanks to a global RNAseq transcriptomic approach on whole snail, we identified a total of 328 differentially expressed genes between resistant and susceptible phenotypes among which 129 were up-regulated and 199 down-regulated. Metabolomic studies were used to corroborate the RNAseq results. The activation of immune genes and specific metabolic pathways in resistant snails might provide them with the capacity to better respond to parasite infection.

Whole genome sequencing of Crassostrea ariakensis (Mollusca: Ostreidae) and C. hongkongensis expands understandings of stress resistance in sessile oysters

To understand the environmental adaptations among sessile bivalves lacking adaptive immunity, a series of analyses were conducted, with special emphasis on the widely distributed C. ariakensis. Employing Pacbio sequencing and Hi-C technologies, whole genome for each of a C. ariakensis (southern China) and C. hongkongensis individual was generated, with the contig N50 reaching 6.2 and 13.0 Mb, respectively. Each genome harbored over 30,000 protein-coding genes, with approximately half of each genome consisting of repeats. Genome alignment suggested possible introgression between C. gigas and C. ariakensis (northern China), and re-sequencing data corroborated this result and indicated significant gene flow between C. gigas and C. ariakensis. These introgressed candidates, well-represented by genes related to immunity and osmotic pressure, may be associated with environmental stresses. Gene family dynamics modeling suggested immune-related genes were well represented among the expanded genes in C. ariakensis. These outcomes could be attributed to the spread of C. ariakensis.

Cloning and characterization of a phosphomevalonate kinase gene that is involved in saponin biosynthesis in the sea cucumber Apostichopus japonicus

The sea cucumber Apostichopus japonicus is one of the most dominant and economically important aquaculture species in China. Saponin, which possesses notable biological and pharmacological properties, is a key determinant of the nutritional and health value of A. japonicus. In the present study, we amplified the full-length cDNA of a phosphomevalonate kinase (PMK) gene (named AjPMK) using rapid amplification of cDNA ends (RACE). Subsequently, we engineered a recombinant AjPMK (rAjPMK) protein and assessed its enzymatic activity by enzyme-linked immunosorbent assay (ELISA). Proteins that interact with rAjPMK were screened and identified via pull-down assay combined with liquid chromatography with tandem mass spectrometry (LC-MS/MS). We found that the full-length cDNA of AjPMK contained 1354 bp and an open reading frame (ORF) of 612 bp. The AjPMK protein was predicted not to contain a signal peptide but to contain a phosphonolate kinase domain seen in higher eukaryotes and a P-loop with a relatively conserved nucleoside triphosphate hydrolase domain. The molecular weight of the AjPMK protein was estimated to be 23.81 kDa, and its isoelectric point was predicted to be 8.72. Phylogenetic analysis showed that AjPMK had a closer evolutionary relationship with genes from starfish than with those of other selected species. Besides, we found that rAjPMK synthesized mevalonate-5-diphosphate, interacted either directly or indirectly with crucial pattern recognition receptors (PRRs) and was regulated by immune-related processes, including antioxidative reactions, stress resistance responses and enzyme hydrolysis. Moreover, AjPMK also interacted with farnesyl pyrophosphate synthase, an enzyme reported to be involved in saponin biosynthesis. Together, our findings implied that AjPMK may be directly involved in saponin biosynthesis and the regulation of various innate immune processes.

Transcriptome analysis reveals new insights into immune response to hypoxia challenge of large yellow croaker (Larimichthys crocea)

Fish live in direct contact with aquatic environment, which exhibits much wider temporal and spatial variations in oxygen content. The molecular mechanisms underlying fish response to hypoxia have become a subject of great concern in recent years. In the present study, we performed transcriptome analysis of spleen and head kidney tissues from large yellow croaker (Larimichthys crocea) at 6 h, 24 h and 48 h after hypoxia challenge. A total of 2,499 and 3,685 differentially expressed genes (DEGs) were obtained in spleen and head kidney, respectively. The expression changes of 10 selected genes in each tissue were further validated by quantitative real-time PCR. Gene ontology and Kyoto Encyclopedia of Genes and Genomes enrichments revealed that numerous DEGs were immune genes, involved in multiple immune-relevant pathways. In spleen, several pattern recognition receptors (PRRs), including Toll-like receptors (TLR1, TLR2-1, TLR2-2, TLR5 and TLR8), Fucolectins (FUCL1, FUCL4 and FUCL5) and macrophage mannose receptor (MRC1), were significantly down-regulated, suggesting that the immune processes mediated by these PRRs may be suppressed by hypoxia stress. However, some PRRs (FUCL4, FUCL5 and MRC1) and other innate immunity genes, such as C-type lectin domain gene family members, chemokines, chemokine receptors and complement components were up-regulated in head kidney, which may be due to the increases in phagocytosis and cytokine secretion by macrophages after hypoxic stimulus. The expression of genes involved in B cell receptor signaling pathway, Natural killer cell-mediated cytotoxicity and NF-κB signaling pathway decreased rapidly, but regained normal or increased over time, suggesting an early adjustment pattern of fish immune response to cope with hypoxia stress. Moreover, the anaerobic ATP-generating pathway was activated and energy consumption processes were repressed concurrently in both spleen and head kidney. These data provide valuable information for understanding the tissue-specific and temporal changes of immune gene expression in hypoxic large yellow croakers.

Divergent immune roles of two fucolectin isoforms in Apostichopus japonicus

The F-type lectin (fucolectin) family represents a new group with innate immunity. In this study, two fucolectin isoforms (designated as AjFTL-1 and AjFTL-2) were identified in sea cucumber (Apostichopus japonicus) through rapid amplification of cDNA ends. Full-length cDNAs of AjFTL-1 and AjFTL-2 measured 2134 and 1286 bp, encoding two secreted proteins comprising 317 and 181 amino acid residues, respectively. The signal peptide, l-fucose binding motif ("HX(26)RXDX(4)R/K") and cation binding sequence motif ("h2DGx") were conserved in AjFTL-1 and AjFTL-2. However, AjFTL-1 contains an additional complement control protein domain. Multiple sequence alignments supported that AjFTL-1 and AjFTL-2 are new members of the F-type lectin family. Tissues distribution analysis indicated that both AjFTL-1 and AjFTL-2 were widely expressed in all tested tissues, featuring differential expression patterns. Vibrio splendidus infection in vivo can significantly upregulate the mRNA transcripts of the two genes, with a larger magnitude observed in AjFTL-1. By contrast, lipopolysaccharide stimulation in vitro can markedly induce the expression level of AjFTL-2 but not that of AjFTL-1. Silencing AjFTL-2 by siRNA can suppress the AjNOS transcript, whereas injection of the recombinant protein of AjFTL-2 can significantly induce AjNOS expression. By contrast, the loss- and gain-of-function of AjFTL-1 caused no effect on the expression of AjNOS. Our present study provides evidence supporting that AjFTL-1 and AjFTL-2 play diverse roles in the innate immune defense of sea cucumbers toward bacterial infection.