Structural and functional analysis of three Iκb kinases (IKK) in disk abalone (Haliotis discus discus): Investigating their role in the innate immune responses

A novel TBK1/IKKϵ is involved in immune response and interacts with MyD88 and MAVS in the scallop Chlamys farreri

Inhibitor of κB kinase (IKK) family proteins are key signaling molecules in the animal innate immune system and are considered master regulators of inflammation and innate immunity that act by controlling the activation of transcription factors such as NF-κB. However, few functional studies on IKK in invertebrates have been conducted, especially in marine mollusks. In this study, we cloned the IKK gene in the Zhikong scallop Chlamys farreri and named it CfIKK3. CfIKK3 encodes a 773-amino acid-long protein, and phylogenetic analysis showed that CfIKK3 belongs to the invertebrate TBK1/IKKϵ protein family. Quantitative real-time PCR analysis showed that CfIKK3 mRNA is ubiquitously expressed in all tested scallop tissues. The expression of CfIKK3 transcripts was significantly induced after challenge with lipopolysaccharide, peptidoglycan, or poly(I:C). Co-immunoprecipitation (co-IP) assays confirmed the direct interaction of CfIKK3 with MyD88 (the key adaptor in the TLR pathway) and MAVS (the key adaptor in the RLR pathway), suggesting that this IKK protein plays a crucial role in scallop innate immune signal transduction. In addition, the CfIKK3 protein formed homodimers and bound to CfIKK2, which may be a key step in the activation of its own and downstream transcription factors. Finally, in HEK293T cells, dual-luciferase reporter gene experiments showed that overexpression of CfIKK3 protein activated the NF-κB reporter gene in a dose-dependent manner. In conclusion, our experimental results confirmed that CfIKK3 could respond to PAMPs challenge and participate in scallop TLR and RLR pathway signaling, ultimately activating NF-κB. Therefore, as a key signaling molecule and modulator of immune activity, CfIKK3 plays an important role in the innate immune system of scallops.

Molecular Cloning and Functional Characterization of Catalase in Stress Physiology, Innate Immunity, Testicular Development, Metamorphosis, and Cryopreserved Sperm of Pacific Abalone

Catalase is a crucial enzyme of the antioxidant defense system responsible for the maintenance of cellular redox homeostasis. The aim of the present study was to evaluate the molecular regulation of catalase (Hdh-CAT) in stress physiology, innate immunity, testicular development, metamorphosis, and cryopreserved sperm of Pacific abalone. Hdh-CAT gene was cloned from the digestive gland (DG) of Pacific abalone. The 2894 bp sequence of Hdh-CAT had an open reading frame of 1506 bp encoding 501 deduced amino acids. Fluorescence in situ hybridization confirmed Hdh-CAT localization in the digestive tubules of the DG. Hdh-CAT was induced by different types of stress including thermal stress, H₂O₂ induction, and starvation. Immune challenges with Vibrio, lipopolysaccharides, and polyinosinic-polycytidylic acid sodium salt also upregulated Hdh-CAT mRNA expression and catalase activity. Hdh-CAT responded to cadmium induced-toxicity by increasing mRNA expression and catalase activity. Elevated seasonal temperature also altered Hdh-CAT mRNA expression. Hdh-CAT mRNA expression was relatively higher at the trochophore larvae stage of metamorphosis. Cryopreserved sperm showed significantly lower Hdh-CAT mRNA expression levels compared with fresh sperm. Hdh-CAT mRNA expression showed a relationship with the production of ROS. These results suggest that Hdh-CAT might play a role in stress physiology, innate immunity, testicular development, metamorphosis, and sperm cryo-tolerance of Pacific abalone.

Transcriptome analysis reveals fluid shear stress (FSS) and atherosclerosis pathway as a candidate molecular mechanism of short-term low salinity stress tolerance in abalone

Background

Transcriptome sequencing is an effective tool to reveal the essential genes and pathways underlying countless biotic and abiotic stress adaptation mechanisms. Although severely challenged by diverse environmental conditions, the Pacific abalone Haliotis discus hannai remains a high-value aquaculture mollusk and a Chinese predominantly cultured abalone species. Salinity is one of such environmental factors whose fluctuation could significantly affect the abalone’s cellular and molecular immune responses and result in high mortality and reduced growth rate during prolonged exposure. Meanwhile, hybrids have shown superiority in tolerating diverse environmental stresses over their purebred counterparts and have gained admiration in the Chinese abalone aquaculture industry.

The objective of this study was to investigate the molecular and cellular mechanisms of low salinity adaptation in abalone. Therefore, this study used transcriptome analysis of the gill tissues and flow cytometric analysis of hemolymph of H. discus hannai (DD) and interspecific hybrid H. discus hannai ♀ x H. fulgens ♂ (DF) during low salinity exposure. Also, the survival and growth rate of the species under various salinities were assessed.

Results

The transcriptome data revealed that the differentially expressed genes (DEGs) were significantly enriched on the fluid shear stress and atherosclerosis (FSS) pathway. Meanwhile, the expression profiles of some essential genes involved in this pathway suggest that abalone significantly up-regulated calmodulin-4 (CaM-4) and heat-shock protein90 (HSP90), and significantly down-regulated tumor necrosis factor (TNF), bone morphogenetic protein-4 (BMP-4), and nuclear factor kappa B (NF-kB).

Also, the hybrid DF showed significantly higher and sustained expression of CaM and HSP90, significantly higher phagocytosis, significantly lower hemocyte mortality, and significantly higher survival at low salinity, suggesting a more active molecular and hemocyte-mediated immune response and a more efficient capacity to tolerate low salinity than DD.

Conclusions

Our study argues that the abalone CaM gene might be necessary to maintain ion equilibrium while HSP90 can offset the adverse changes caused by low salinity, thereby preventing damage to gill epithelial cells (ECs).

The data reveal a potential molecular mechanism by which abalone responds to low salinity and confirms that hybridization could be a method for breeding more stress-resilient aquatic species.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08611-8.

Scallop IKK1 Responds to Bacterial and Virus-Related Pathogen Stimulation and Interacts With MyD88 Adaptor of Toll-Like Receptor Pathway Signaling

IKK proteins are key signaling molecules in the innate immune system of animals, and act downstream of pattern recognition receptors. However, research on IKKs in invertebrates, especially marine mollusks, remains scarce. In this study, we cloned CfIKK1 gene from the Zhikong scallop (Chlamys farreri) and studied its function and the signaling it mediates. The open reading frame of CfIKK1 was 2190 bp and encoded 729 amino acids. Phylogenetic analysis showed that CfIKK1 belonged to the invertebrate IKKα/IKKβ family. Quantitative real-time PCR analysis revealed the ubiquitous expression of CfIKK1 mRNA in all scallop tissues and challenge with lipopolysaccharide, peptidoglycan, or poly(I:C) significantly upregulated the expression of CfIKK1. Co-immunoprecipitation assays confirmed the interaction of CfIKK1 with scallop MyD88 (Myeloid differentiation actor 88, the key adaptor of the TLR signaling pathway) via its N-terminal kinase domain. Additionally, CfIKK1 protein could form homodimers and even oligomers, with N-terminal kinase domain and C-terminal scaffold dimerization domain playing key roles in this process. Finally, the results of RNAi experiments showed that when the scallop IKK1 gene was suppressed, the expression of IRF genes also decreased significantly. In conclusion, CfIKK1 could respond to PAMPs challenge and interact with MyD88 protein of scallop TLR signaling, with the formation of CfIKK1 dimers or oligomers. At the same time, the results of RNAi experiments revealed the close regulatory relationship between IKK1 and IRF genes of scallop. Therefore, as a key signal transduction molecule and immune activity regulator, CfIKK1 plays important roles in the innate immune system of scallops.