Characterization of allograft inflammatory factor-1 in Hyriopsis cumingii and its expression in response to immune challenge and pearl sac formation

A proteomic approach reveals biomineralization and immune response for mantle to pearl sac in the freshwater pearl mussel (Hyriopsis cumingii)

In the process of production of freshwater pearl, implanted mantle pieces undergo a series of complex physiological and biochemical processes to form pearl sac, which produce pearl. This is a very important site of occurrence due to immune-induced biomineralization, while its molecular regulatory mechanism is still unclear. Here, we use proteomics to identify differentially expressed proteins (DEPs) of the mantle and pearl sac and examine the biomineralization and immune response of the pearl sac formation process in Hyriopsis cumingii. Using iTRAQ technology and bioinformatics analysis, we obtained DEP profiles between the mantle and pearl sac. A total of 1871 proteins were identified. Of these, 74 DEPs were found between the pearl sac and outer mantle, 112 DEPs between the pearl sac and inner mantle, and 124 DEPs between the outer and inner mantles. Bioinformatics analysis revealed that the screened biomineralization-related DEPs were mainly enriched in signaling pathways associated with calcium signaling, regulation of the actin cytoskeleton and protein processing in the endoplasmic reticulum, while the immune-related DEPs were mainly enriched in the Notch, Hippo, nuclear factor kappa-B (NF-κB), and transforming growth factor-β (TGF-β) signaling pathways. In addition, the expression of six biomineralization-related and four immune-related proteins were verified at the transcriptional level using quantitative real-time PCR. Our findings contribute to furthering the understanding of the mechanisms of pearl formation and immune response, and have long-term implications for future studies on the production of high-quality freshwater pearls and development of the freshwater pearl industry.

Allograft Inflammatory Factor-1 in Metazoans: Focus on Invertebrates

Simple Summary

During their life, all living organisms defend themselves from pathogens using complex strategies. Vertebrates and invertebrates share mechanisms and molecules that guarantee their overall bodily integrity. Allograft inflammatory factor-1 (AIF-1) is a protein extensively studied in vertebrates, and especially in mammals. This factor, generally involved in inflammation events occurring upon pathogenic infection or tissue injury, is linked to several important human diseases. This review collects data on the presence and role of AIF-1 in invertebrates, which are still poorly investigated organisms. Multiple alignment and phylogenetic analysis reveal that AIF-1 is conserved in vertebrates and invertebrates, suggesting similarity of functions. In some invertebrate species, the expression of AIF-1 increases considerably after a bacterial challenge, indicating that it plays a key role during the immune responses. This review highlights the importance of studying this protein in invertebrates as a way to improve our knowledge of innate immunity mechanisms and to better understand inflammatory regulation events in mammals.

Abstract

Allograft inflammatory factor-1 (AIF-1) is a calcium-binding scaffold/adaptor protein often associated with inflammatory diseases. Originally cloned from active macrophages in humans and rats, this gene has also been identified in other vertebrates and in several invertebrate species. Among metazoans, AIF-1 protein sequences remain relatively highly conserved. Generally, the highest expression levels of AIF-1 are observed in immunocytes, suggesting that it plays a key role in immunity. In mammals, the expression of AIF-1 has been reported in different cell types such as activated macrophages, microglial cells, and dendritic cells. Its main immunomodulatory role during the inflammatory response has been highlighted. Among invertebrates, AIF-1 is involved in innate immunity, being in many cases upregulated in response to biotic and physical challenges. AIF-1 transcripts result ubiquitously expressed in all examined tissues from invertebrates, suggesting its participation in a variety of biological processes, but its role remains largely unknown. This review aims to present current knowledge on the role and modulation of AIF-1 and to highlight its function along the evolutionary scale.

Diminished adherence of Biomphalaria glabrata embryonic cell line to sporocysts of Schistosoma mansoni following programmed knockout of the allograft inflammatory factor

BACKGROUND

Larval development in an intermediate host gastropod snail of the genus Biomphalaria is an obligatory component of the life-cycle of Schistosoma mansoni. Understanding of the mechanism(s) of host defense may hasten the development of tools that block transmission of schistosomiasis. The allograft inflammatory factor 1, AIF, which is evolutionarily conserved and expressed in phagocytes, is a marker of macrophage activation in both mammals and invertebrates. AIF enhances cell proliferation and migration. The embryonic cell line, termed Bge, from Biomphalaria glabrata is a versatile resource for investigation of the snail-schistosome relationship since Bge exhibits a hemocyte-like phenotype. Hemocytes perform central roles in innate and cellular immunity in gastropods and in some cases can kill the parasite. However, the Bge cells do not kill the parasite in vitro.

METHODS

Bge cells were transfected by electroporation with plasmid pCas-BgAIFx4, encoding the Cas9 nuclease and a guide RNA specific for exon 4 of the B. glabrata AIF (BgAIF) gene. Transcript levels for Cas9 and for BgAIF were monitored by reverse-transcription-PCR and, in parallel, adhesion of gene-edited Bge cells during co-culture with of schistosome sporocysts was assessed.

RESULTS

Gene knockout manipulation induced gene-disrupting indels, frequently 1-2 bp insertions and/or 8-30 bp deletions, at the programmed target site; a range from 9 to 17% of the copies of the BgAIF gene in the Bge population of cells were mutated. Transcript levels for BgAIF were reduced by up to 73% (49.5 ± 20.2% SD, P ≤ 0.05, n = 12). Adherence by BgAIF gene-edited (ΔBgAIF) Bge to sporocysts diminished in comparison to wild type cells, although cell morphology did not change. Specifically, as scored by a semi-quantitative cell adherence index (CAI), fewer ΔBgAIF than control wild type cells adhered to sporocysts; control CAI, 2.66 ± 0.10, ΔBgAIF, 2.30 ± 0.22 (P ≤ 0.01).

CONCLUSIONS

The findings supported the hypothesis that BgAIF plays a role in the adherence of B. glabrata hemocytes to sporocysts during schistosome infection in vitro. This demonstration of the activity of programmed gene editing will enable functional genomics approaches using CRISPR/Cas9 to investigate additional components of the snail-schistosome host-parasite relationship.

Integrated transcriptome analysis of immunological responses in the pearl sac of the triangle sail mussel (Hyriopsis cumingii) after mantle implantation

For pearl culture of bivalve Hyriopsis cumingii, implantation of the sabio may cause nucleus discharge and increased host death rates. We performed a transcriptome analysis of the pearl sac of H. cumingii for 30 days after mantle implantation; 293863 unigenes were obtained, and 27176 unigenes were identified using nr, nt, KO, Swiss-Prot, Pfam, GO, and KOG databases. We detected 4878 differentially expressed genes (DEGs) through pairwise comparisons. We speculated that the physical condition of the recipient mussels returned to normal in about one month; the period was divided into six vital phases (0, 2 h-6 h, 12 h-24 h, 48 h to 7 days, 14 days and 30 days) on the basis of the overall similarities in DEGs. We compared the DEGs between time points and identified key immune-related genes. Our findings provide information on the immunological reactions induced by implantation in pearl mussels.

Identification of tumor necrosis factor receptor-associated factor 6 in the pearl mussel Hyriopsis cumingii and its involvement in innate immunity and pearl sac formation

Tumor necrosis factor receptor-associated factor 6 (TRAF6) acts as a central intracellular signal adapter molecule that mediates the tumor necrosis factor receptor superfamily and the interleukin-1 receptor/Toll-like receptor family in vertebrates and invertebrates. In the present study, HcTRAF6, a molluscan homologue of TRAF6 from Hyriopsis cumingii, has been cloned and identified. The entire open reading frame of HcTRAF6 was found to comprise a 1965-bp region that encodes a predicted protein of 654 amino acids, which contains conserved characteristic domains including a RING domain, two TRAF-type zinc finger domains, a typical coiled coil and the MATH domain. Phylogenetic analysis revealed that HcTRAF6 was aggregated closely with CsTRAF6 from Cyclina sinensis in the invertebrate cluster of mollusks. Further, qRT-PCR analysis showed that HcTRAF6 mRNA was extensively distributed in mussel tissues with a high expression in gills. After immune stimulation with Aeromonas hydrophila and lipopolysaccharides, the transcription of HcTRAF6 was obviously induced in the gills and hemocytes. In addition, significant fluctuation in HcTRAF6 expression was observed in the pearl sac, gills and hemocytes after mantle implantation. These findings confirmed its role in the alloimmune response. Dual-luciferase reporter assay showed that over-expression of HcTRAF6 could enhance the activity of the NF-κB reporter in a dose-dependent manner. Further, the RNA interference showed that the up-regulation of antimicrobial peptides in anti-bacterial infection was strongly suppressed in HcTRAF6-silenced mussels and that depletion of HcTRAF inhibited the elimination of A. hydrophila. All these findings together prove that HcTRAF6 functions as an efficient regulator in innate immune mechanisms against invading pathogens and the alloimmune mechanism after mantle implantation in H. cumingii.

Three newly identified galectin homologues from triangle sail mussel (Hyriopsis cumingii) function as potential pattern-recognition receptors

Galactoside-binding lectins, also known as galectins, play crucial roles in innate immune response in invertebrates. In this study, three cDNA sequences from Hyriopsis cumingii were identified and collectively called HcGalec genes. Each of the three deduced HcGalec proteins contained a galactose-binding lectin domain or a GLECT domain. All the three HcGalec genes are mainly present in the hepatopancreas and gills, and their expression is induced at 24 h after bacterial challenge. Three recombinant HcGalec proteins can bind and agglutinate (Ca²⁺-dependent) various microorganisms, including Gram-positive and Gram-negative bacteria. These proteins can attach to mannan and peptidoglycan. Meanwhile, the expression of the three HcGalec genes in the gills were significantly down-regulated after dsRNA interference (HcGalec1-RNAi, HcGalec2-RNAi, and HcGalec3-RNAi) and Vibrio parahaemolyticus injection. The expression levels of some antimicrobial peptides, including lysozyme 1 and lysozyme 2, were also markedly decreased after dsRNA interference. Overall, these results suggested that these three HcGalec proteins may function as potential receptors participating in the innate immune responses of H. cumingii against bacterial infection.

Molecular and expression analysis of the Allograft inflammatory factor 1 (AIF-1) in the coelomocytes of the common sea urchin Paracentrotus lividus

Allograft inflammatory factor 1 (AIF-1) is a highly conserved gene involved in inflammation, cloned and characterized in several evolutionary distant animal species. Here, we report the molecular identification, characterization and expression of AIF-1 from the common sea urchin Paracentrotus lividus. In this species, AIF-1 encodes a predicted 151 amino acid protein with high similarity to vertebrate AIF-1 proteins. Immunocytochemical analyses on coelomocytes reveal localization of the AIF-1 protein in amoebocytes (perinuclear cytoplasmic zone) and red sphaerulocytes (inside granules), but not in vibratile cells and colorless sphaerula cells. The significant increase of AIF-1 expression (mRNA and protein) found in the coelomocytes of the sea urchin after Gram + bacterial challenge suggests the involvement of AIF-1 in the inflammatory response. Our analysis on P. lividus AIF-1 contributes to elucidate AIF-1 function along the evolutionary scale and consolidate the key evolutionary position of echinoderms throughout metazoans with respect to the common immune paths.