Molecular characterization and biological effect of a C-type lectin receptor in Qihe crucian carp, Carassius auratus

Identification of potential geosmin-binding proteins in grass carp gill based on affinity responsive target stability and tandem mass tag proteomics

The escalating issue of water pollution, especially the accumulation of organic off-flavor pollutants, poses significant challenges. Geosmin, a typical off-flavor compound in aquatic environments, not only compromises the quality of aquatic products but also deters consumers. Its impact extends to aquatic organisms, with current research focusing on dose-response and ecotoxicity, while neglecting the molecular-level study of geosmin-binding proteins. This study employs an integrated approach combing affinity-responsive target stability in vitro, tandem mass tag proteomics in vivo, and molecular docking to identify geosmin-binding proteins in the gill tissue of grass carp (Ctenopharyngodon idella). ARTS analysis identified 56 proteins, predominantly membrane-associated proteins, such as catenin beta-1, annexin, and integrin beta. Proteomic analysis revealed 256 differentially expressed proteins in geosmin-exposure group, with 18 common proteins screened by in vivo and in vitro methods. Among these, annexin, cathepsin D, and interleukin-1 receptors were highlighted as potential geosmin targets, with annexin demonstrating the highest binding affinity in silico. This study provides a robust protocol integrating in vivo, in vitro, and in silico approaches to elucidate geosmin's target proteins in grass carp gill tissue, advancing our understanding of pollutant-biological interactions and enhancing environmental risk assessment accuracy.

The Exploration of Joint Toxicity and Associated Mechanisms of Primary Microplastics and Methamphetamine in Zebrafish Larvae

The co-existence of microplastics (MPs) and methamphetamine (METH) in aquatic ecosystems has been widely reported; however, the joint toxicity and associated mechanisms remain unclear. Here, zebrafish larvae were exposed individually or jointly to polystyrene (PS) and polyvinyl chloride (PVC) MPs (20 mg/L) and METH (1 and 5 mg/L) for 10 days. The mortality, behavioral functions, and histopathology of fish from different groups were determined. PS MPs posed a stronger lethal risk to fish than PVC MPs, while the addition of METH at 5 mg/L significantly increased mortality. Obvious deposition of MPs was observed in the larvae's intestinal tract in the exposure groups. Meanwhile, treatment with MPs induced intestinal deposits and intestinal hydrops in the fish, and this effect was enhanced with the addition of METH. Furthermore, MPs significantly suppressed the locomotor activation of zebrafish larvae, showing extended immobility duration and lower velocity. METH stimulated the outcome of PS but had no effect on the fish exposed to PVC. However, combined exposure to MPs and METH significantly increased the turn angle, which declined in individual MP exposure groups. RNA sequencing and gene quantitative analysis demonstrated that exposure to PS MPs and METH activated the MAPK signaling pathway and the C-type lectin signaling pathway of fish, while joint exposure to PVC MPs and METH stimulated steroid hormone synthesis pathways and the C-type lectin signaling pathway in zebrafish, contributing to cellular apoptosis and immune responses. This study contributes to the understanding of the joint toxicity of microplastics and pharmaceuticals to zebrafish, highlighting the significance of mitigating microplastic pollution to preserve the health of aquatic organisms and human beings.

A C-type lectin-like receptor CD302 in yellow drum (Nibea albiflora) functioning in antibacterial activity and innate immune signaling

Molecular dissection of disease resistance against Vibrio harveyi infection in yellow drum at the genome-wide level uncovered a C-type lectin-like receptor cluster of differentiation CD302 (named as YdCD302) in our previous study. Here, the gene expression pattern of YdCD302 and its function in mediating the defense response to V. harveyi attack were investigated. Gene expression analysis demonstrated that YdCD302 was ubiquitously distributed in various tissues with the highest transcript abundance in liver. The YdCD302 protein exhibited agglutination and antibacterial activity against V. harveyi cells. Binding assay indicated that YdCD302 can physically interact with V. harveyi cells in a Ca2+-independent manner, and the interaction can activate reactive oxygen species (ROS) production in the bacterial cells to induce RecA/LexA-mediated cell death. After infection with V. harveyi, the expression of YdCD302 can be up-regulated significantly in the main immune organs of yellow drum and potentially further trigger the cytokines involved innate immunity. These findings provide insight into the genetic basis of the disease resistance trait in yellow drum and shed light on the functioning of the CD302 C-type lectin-like receptor in host-pathogen interactions. The molecular and functional characterization of YdCD302 is a significant step towards a better understanding of disease resistance mechanisms and the development of new strategies for disease control.

Molecular characterization and functional analysis of CD209E from Nile Tilapia (Oreochromis Niloticus) involved in immune response to bacterial infection

CD209 plays significant roles in pathogen recognition, innate and adaptive immunity, and cell-cell interactions. In the present study, a CD209 antigen-like protein E from Nile tilapia (Oreochromis niloticus) (designated as OnCD209E) was identified and characterized. OnCD209E contains an open reading frame (ORF) of 771 bp encoding a 257 amino acid protein, as well as the carbohydrate recognition domain (CRD). Multiple sequence analysis exhibits that the amino acid sequence of OnCD209E was relatively high homologous to that of partial fish, especially the highly conserved CRD, in which four conserved disulfide-bonded cysteine residues, WIGL conserved motif and two Ca²⁺/carbohydrate-binding sites (EPD and WFD motifs) were founded. Quantitative real-time PCR and Western Blot revealed that OnCD209E mRNA/protein is generally expressed in all tissues examined, but with wealth in head kidney and spleen tissues. The mRNA expression of OnCD209E was significantly increased in brain, head kidney, intestine, liver, and spleen tissues in response to the stimulation with polyinosinic-polycytidylic acid, Streptococcus agalactiae and Aeromonas hydrophila in vitro. Recombinant OnCD209E protein exhibited detectable bacterial binding and agglutination activity against different bacteria as well as inhibited the proliferation of tested bacteria. Subcellular localization analysis revealed that OnCD209E was mostly localized in the cell membrane. Moreover, overexpression of OnCD209E could activate nuclear factor-kappa B reporter genes in HEK-293T cells. Collectively, these results demonstrated that CD209E may potentially involve in immune response of Nile tilapia against bacterial infection.

A novel l-rhamnose-binding lectin participates in defending against bacterial infection in zebrafish

l-rhamnose-binding lectin (RBL), which is a class of animal lectins independent of Ca²⁺, can specifically bind l-rhamnose or d-galactose. Although several lectins in zebrafish have been reported, their functional mechanisms have not been fully uncovered. In this study, we discovered a novel l-rhamnose binding lectin (DrRBL) and studied its innate immune function. The DrRBL protein contains only one carbohydrate-recognition domain (CRD), which includes two strictly conserved motifs, "YGR" and "DPC". DrRBL was detected in all tested tissues and was present at high levels in the spleen, hepatopancreas and skin. After Aeromonas hydrophila challenge, the DrRBL mRNA level was significantly upregulated. Additionally, DrRBL was secreted into the extracellular matrix. Recombinant DrRBL (rDrRBL) could significantly inhibit the growth of gram-positive/negative bacteria, bind to several bacteria and cause obvious agglutination. The rDrRBL protein could combine with polysaccharides, such as PGN and LPS, rather than LTA. A more detailed study showed that rDrRBL could combine with monosaccharides, such as mannose, rhamnose and glucose, which are important components of PGN and LPS. However, rDrRBL could not bind to ribitol, which is an important component of LTA. The DrRBL deletion mutants, DrRBL^Δ144-150 and DrRBL^Δ198-200, were also constructed. DrRBL^Δ144-150 ("ANYGRTD" deficient) showed weak bacterial inhibiting ability. However, DrRBL^Δ198-200 ("DPC" deficient) showed weak agglutination ability. These results suggest that the "DPC" domain is important for agglutination. The conserved domain "ANYGRTD" is essential for inhibiting bacterial growth.