Autophagy and apoptosis induced by Chinese giant salamander (Andrias davidianus) iridovirus (CGSIV)

Assessing the biogeography of marine giant viruses in four oceanic transects

Viruses of the phylum Nucleocytoviricota are ubiquitous in ocean waters and play important roles in shaping the dynamics of marine ecosystems. In this study, we leveraged the bioGEOTRACES metagenomic dataset collected across the Atlantic and Pacific Oceans to investigate the biogeography of these viruses in marine environments. We identified 330 viral genomes, including 212 in the order Imitervirales and 54 in the order Algavirales. We found that most viruses appeared to be prevalent in shallow waters (<150 m), and that viruses of the Mesomimiviridae (Imitervirales) and Prasinoviridae (Algavirales) are by far the most abundant and diverse groups in our survey. Five mesomimiviruses and one prasinovirus are particularly widespread in oligotrophic waters; annotation of these genomes revealed common stress response systems, photosynthesis-associated genes, and oxidative stress modulation genes that may be key to their broad distribution in the pelagic ocean. We identified a latitudinal pattern in viral diversity in one cruise that traversed the North and South Atlantic Ocean, with viral diversity peaking at high latitudes of the northern hemisphere. Community analyses revealed three distinct Nucleocytoviricota communities across latitudes, categorized by latitudinal distance towards the equator. Our results contribute to the understanding of the biogeography of these viruses in marine systems.

Assessing the biogeography of marine giant viruses in four oceanic transects

Viruses of the phylum Nucleocytoviricota are ubiquitous in ocean waters and play important roles in shaping the dynamics of marine ecosystems. In this study, we leveraged the bioGEOTRACES metagenomic dataset collected across the Atlantic and Pacific Oceans to investigate the biogeography of these viruses in marine environments. We identified 330 viral genomes, including 212 in the order Imitervirales and 54 in the order Algavirales . We found that most viruses appeared to be prevalent in shallow waters (<150 meters), and that viruses of the Mesomimiviridae ( Imitervirales ) and Prasinoviridae ( Algavirales ) are by far the most abundant and diverse groups in our survey. Five mesomimiviruses and one prasinovirus are particularly widespread in oligotrophic waters; annotation of these genomes revealed common stress response systems, photosynthesis-associated genes, and oxidative stress modulation that may be key to their broad distribution in the pelagic ocean. We identified a latitudinal pattern in viral diversity in one cruise that traversed the North and South Atlantic Ocean, with viral diversity peaking at high latitudes of the northern hemisphere. Community analyses revealed three distinct Nucleocytoviricota communities across latitudes, categorized by latitudinal distance towards the equator. Our results contribute to the understanding of the biogeography of these viruses in marine systems.

Non-pathogenic grass carp reovirus infection leads to both apoptosis and autophagy in a grass carp cell line

A novel GCRV strain isolated from healthy grass carp was named as grass carp reovirus - HH196 (GCRV-HH196), and its infection mechanism remains unclear. In this study, the grass carp ovary cell line (GCO cells) was used to investigate the cell death involved in GCRV-HH196 infection. The results showed that DNA damage, cells volume reduction and cytoplasm shrinkage happened during GCRV-HH196 infection. The mRNA expression levels of pro-apoptotic genes were up-regulated during infection. Two initiators of apoptosis, caspase 8 and caspase 9, and the executioner of apoptosis, caspase 3, were all significantly activated in GCRV-HH196-infected cells. Flow cytometry analysis showed that the number of apoptotic cells in infected cells was significantly higher than that in control cells as the infection progress. Meanwhile, autophagy was also involved in the regulation of GCRV - HH196 infection. We observed that LC3 puncta existed in cytoplasm in GCRV-HH196-infected cells. Furthermore, the protein level of LC3-Ⅱ and Beclin-1 increased, while that of p-Akt decreased in GCRV-HH196-infected cells. These results demonstrated that GCRV-HH196 may regulate apoptosis and autophagy for the virus proliferation and spread, which set a foundation for further research on the interaction between GCRV-HH196 and host.

Patterns of infection, origins, and transmission of ranaviruses among the ectothermic vertebrates of Asia

Ranaviral infections, a malady of ectothermic vertebrates, are becoming frequent, severe, and widespread, causing mortality among both wild and cultured species, raising odds of species extinctions and economic losses. This increase in infection is possibly due to the broad host range of ranaviruses and the transmission of these pathogens through regional and international trade in Asia, where outbreaks have been increasingly reported over the past decade. Here, we focus attention on the origins, means of transmission, and patterns of spread of this infection within the region. Infections have been recorded in both cultured and wild populations in at least nine countries/administrative regions, together with mass die-offs in some regions. Despite the imminent seriousness of the disease in Asia, surveillance efforts are still incipient. Some of the viral strains within Asia may transmit across host-taxon barriers, posing a significant risk to native species. Factors such as rising temperatures due to global climate change seem to exacerbate ranaviral activity, as most known outbreaks have been recorded during summer; however, data are still inadequate to verify this pattern for Asia. Import risk analysis, using protocols such as Pandora+, pre-border pathogen screening, and effective biosecurity measures, can be used to mitigate introduction of ranaviruses to uninfected areas and curb transmission within Asia. Comprehensive surveillance using molecular diagnostic tools for ranavirus species and variants will help in understanding the prevalence and disease burden in the region. This is an important step toward conserving native biodiversity and safeguarding the aquaculture industry.

Host-virus interactions and defense mechanisms for giant viruses

Giant viruses, with virions larger than 200 nm and genomes larger than 340 kilobase pairs, modified the now outdated perception of the virosphere. With virions now reported reaching up to 1.5 μm in size and genomes of up to 2.5 Mb encoding components shared with cellular life forms, giant viruses exhibit a complexity similar to microbes, such as bacteria and archaea. Here, we review interactions of giant viruses with their hosts and defense strategies of giant viruses against their hosts and coinfecting microorganisms or virophages. We also searched by comparative genomics for homologies with proteins described or suspected to be involved in defense mechanisms. Our search reveals that natural immunity and apoptosis seem to be crucial components of the host defense against giant virus infection. Conversely, giant viruses possess methods of hijacking host functions to counteract cellular antiviral responses. In addition, giant viruses may encode other unique and complex pathways to manipulate the host machinery and eliminate other competing microorganisms. Notably, giant viruses have evolved defense mechanisms against their virophages and they might trigger defense systems against other viruses through sequence integration. We anticipate that comparative genomics may help identifying genes involved in defense strategies of both giant viruses and their hosts.

Chinese Giant Salamander (Andrias davidianus) Iridovirus Infection Leads to Apoptotic Cell Death through Mitochondrial Damage, Caspases Activation, and Expression of Apoptotic-Related Genes

Chinese giant salamander iridovirus (GSIV) is the causative pathogen of Chinese giant salamander (Andrias davidianus) iridovirosis, leading to severe infectious disease and huge economic losses. However, the infection mechanism by GSIV is far from clear. In this study, a Chinese giant salamander muscle (GSM) cell line is used to investigate the mechanism of cell death during GSIV infection. Microscopy observation and DNA ladder analysis revealed that DNA fragmentation happens during GSIV infection. Flow cytometry analysis showed that apoptotic cells in GSIV-infected cells were significantly higher than that in control cells. Caspase 8, 9, and 3 were activated in GSIV-infected cells compared with the uninfected cells. Consistently, mitochondria membrane potential (MMP) was significantly reduced, and cytochrome c was released into cytosol during GSIV infection. p53 expression increased at an early stage of GSIV infection and then slightly decreased late in infection. Furthermore, mRNA expression levels of pro-apoptotic genes participating in the extrinsic and intrinsic pathway were significantly up-regulated during GSIV infection, while those of anti-apoptotic genes were restrained in early infection and then rose in late infection. These results collectively indicate that GSIV induces GSM apoptotic cell death involving mitochondrial damage, caspases activation, p53 expression, and pro-apoptotic molecules up-regulation.

Interactions between Autophagy and DNA Viruses

Autophagy is a catabolic biological process in the body. By targeting exogenous microorganisms and aged intracellular proteins and organelles and sending them to the lysosome for phagocytosis and degradation, autophagy contributes to energy recycling. When cells are stimulated by exogenous pathogenic microorganisms such as viruses, activation or inhibition of autophagy is often triggered. As autophagy has antiviral effects, many viruses may escape and resist the process by encoding viral proteins. At the same time, viruses can also use autophagy to enhance their replication or increase the persistence of latent infections. Here, we give a brief overview of autophagy and DNA viruses and comprehensively review the known interactions between human and animal DNA viruses and autophagy and the role and mechanisms of autophagy in viral DNA replication and DNA virus-induced innate and acquired immunity.

Rapid detection of giant salamander iridovirus by cross-priming amplification

Giant salamander iridovirus (GSIV) belongs to the epizootic genus Ranavirus, and is the cause of epidemic diseases associated with high mortality and great losses to artificial breeding and farming. Here, we established a simple, accurate, and reliable cross-priming amplification (CPA) method to detect GSIV. The CPA assay targets the major caspid protein gene of the GSIV genome to design crossing primer pairs, and the reaction conditions were optimized, including optimal concentrations of the primers, betaine, dNTPs, Mg²⁺, and Bst DNA polymerase, and reaction conditions. The sensitivity was shown to be 10 times higher than that of conventional polymerase chain reaction (PCR), and the specificity was 100%. The results were identified on nucleic acid strips within 3-5 min. Application of the CPA and PCR to 54 samples of giant salamander showed a positive rate of 72.22% and 74.07%, respectively, demonstrating high coincidence (94.44%, kappa = 8.7, P < 0.0001). The sensitivity of the CPA assay was 97.50% and the specificity was 92.86%. Thus, the CPA assay is as effective as conventional PCR, but with added practical advantages of simplicity and an almost instrument-free platform, which will be useful for both laboratories and giant salamander farms.

Autophagy induced by avian reovirus enhances viral replication in chickens at the early stage of infection

BACKGROUND

Avian reovirus (ARV) is an important pathogen that can cause serious disease in poultry. Though several in vitro studies revealed some molecular mechanisms that are responsible for ARV-induced autophagy, it is still largely unknown how ARV manipulates autophagy to promote its own propagation.

RESULTS

In this study, we demonstrated that ARV infection triggered autophagy in chicken tissues, evident from the enhancement of LC3-I/-II conversion and the appearance of abundant autophagosomes. Moreover, viral replication and the expression of IL-1β were coupled with the process of ARV-induced autophagy in the early stage of infection. Furthermore, regulation of autophagy affected the accumulation of LC3-II, the production of ARV and the expression of IL-1β.

CONCLUSIONS

Altogether, our data suggest that ARV induces autophagy, which benefits its replication and dissemination in chicken tissues at the early infection stage.

Common midwife toad ranaviruses replicate first in the oral cavity of smooth newts (Lissotriton vulgaris) and show distinct strain-associated pathogenicity

Ranavirus is the second most common infectious cause of amphibian mortality. These viruses affect caudates, an order in which information regarding Ranavirus pathogenesis is scarce. In the Netherlands, two strains (CMTV-NL I and III) were suspected to possess distinct pathogenicity based on field data. To investigate susceptibility and disease progression in urodeles and determine differences in pathogenicity between strains, 45 adult smooth newts (Lissotriton vulgaris) were challenged via bath exposure with these ranaviruses and their detection in organs and feces followed over time by PCR, immunohistochemistry and in situ hybridization. Ranavirus was first detected at 3 days post infection (p.i.) in the oral cavity and upper respiratory mucosa. At 6 days p.i, virus was found in connective tissues and vasculature of the gastrointestinal tract. Finally, from 9 days p.i onwards there was widespread Ranavirus disease in various organs including skin, kidneys and gonads. Higher pathogenicity of the CMTV-NL I strain was confirmed by higher correlation coefficient of experimental group and mortality of challenged animals. Ranavirus-exposed smooth newts shed virus in feces intermittently and infection was seen in the absence of lesions or clinical signs, indicating that this species can harbor subclinical infections and potentially serve as disease reservoirs.

Aquatic animal viruses mediated immune evasion in their host

Viruses are important and lethal pathogens that hamper aquatic animals. The result of the battle between host and virus would determine the occurrence of diseases. The host will fight against virus infection with various responses such as innate immunity, adaptive immunity, apoptosis, and so on. On the other hand, the virus also develops numerous strategies such as immune evasion to antagonize host antiviral responses. Here, We review the research advances on virus mediated immune evasions to host responses containing interferon response, NF-κB signaling, apoptosis, and adaptive response, which are executed by viral genes, proteins, and miRNAs from different aquatic animal viruses including Alloherpesviridae, Iridoviridae, Nimaviridae, Birnaviridae, Reoviridae, and Rhabdoviridae. Thus, it will facilitate the understanding of aquatic animal virus mediated immune evasion and potentially benefit the development of novel antiviral applications.

Iridoviral infection can be reduced by UCHL1-loaded exosomes from the testis of Chinese giant salamanders (Andrias davidianus)

Chinese giant salamander iridovirus (CGSIV) is a large double-stranded DNA virus that infects Chinese giant salamanders (CGSs) and is responsible for a high mortality rate of CGSs under certain conditions. It is generally believed that CGSIV is a horizontally transmitting virus that affects lower vertebrates. Exosomes from tissues and cells affect the mechanism of viral infections. UCHL1, a deubiquitinating enzyme, is indirectly involved in virus propagation via cytokine and chemokine suppression. In our study, a few CGSIVs were detected in the testis of the special symptom CGSs using PCR and immunofluorescence analysis. The exosomes originating in the testicular fluid was isolated and identified using the Nanosight NS300 system and scanning electron microscopy. The UCHL1-loaded exosomes may resist CGSIV entry by fusing with and remodeling CGSIV. UCHL1 in the primary testicular fibroblasts was maintained at a stable level to inhibit the infection and replication of CGSIV by secreting and sorting exosomes. These data provided a new insight into CGSIV being a type of horizontally transmitting virus.

Protective Immunity Induced by DNA Vaccination against Ranavirus Infection in Chinese Giant Salamander Andrias davidianus

Andrias davidianus ranavirus (ADRV) is an emerging viral pathogen that causes severe systemic hemorrhagic disease in Chinese giant salamanders. There is an urgent need for developing an effective vaccine against this fatal disease. In this study, DNA vaccines containing the ADRV 2L gene (pcDNA-2L) and the 58L gene (pcDNA-58L) were respectively constructed, and their immune protective effects were evaluated in Chinese giant salamanders. In vitro and in vivo expression of the vaccine plasmids were confirmed in transfected cells and muscle tissues of vaccinated Chinese giant salamanders by using immunoblot analysis or RT-PCR. Following ADRV challenge, the Chinese giant salamanders vaccinated with pcDNA-2L showed a relative percent survival (RPS) of 66.7%, which was significant higher than that in Chinese giant salamanders immunized with pcDNA-58L (RPS of 3.3%). Moreover, the specific antibody against ADRV was detected in Chinese giant salamanders vaccinated with pcDNA-2L at 14 and 21 days post-vaccination by indirect enzyme-linked immunosorbent assay (ELISA). Transcriptional analysis revealed that the expression levels of immune-related genes including type I interferon (IFN), myxovirus resistance (Mx), major histocompatibility complex class IA (MHCIA), and immunoglobulin M (IgM) were strongly up-regulated after vaccination with pcDNA-2L. Furthermore, vaccination with pcDNA-2L significantly suppressed the virus replication, which was seen by a low viral load in the spleen of Chinese giant salamander survivals after ADRV challenge. These results indicated that pcDNA-2L could induce a significant innate immune response and an adaptive immune response involving both humoral and cell-mediated immunity that conferred effective protection against ADRV infection, and might be a potential vaccine candidate for controlling ADRV disease in Chinese giant salamanders.

UCHL1 expression and localization on testicular development and spermatogenesis of Chinese giant salamanders

Ubiquitin carboxyl-terminal hydrolase L1 (UCHL1), which is extensively expressed in vertebrates, is a deubiquitinating enzymes that inhibits the degradation of proteins by reversing ubiquitination modification. Herein, a 1087-bp sequence encoding UCHL1 was identified from the Chinese giant salamander (CGS; Andrias davidianus). The coding sequences (CDS) of UCHL1 encoded a putative poly peptide of 222 amino acids. The CGS UCHL1 isoforms were more related to their human and mouse counterparts. The phylogenic tree of vertebrate UCHL1 indicated that CGS UCHL1 has the closest relationship with human UCHL1 (up to 73.99 %). Before the gonads of male CGSs matured, the peak level of UCHL1 expression in testes appeared in 3-year-old CGSs according to RT-qPCR and western blot. In adult testes, the level of UCHL1 protein was lower in the breeding period than in the post-breeding period, whereas the level of UCHL1 protein in interstitial fluid of adult CGS testes was higher during the breeding period than during the post-breeding period. In testicular seminiferous lobules in the developmental stage of CGSs, immunohistochemistry displayed three kinds of localizing patterns of UCHL1, including nuclear localization at half year old, cytoplasmic localization from one year to three years old, and extracellular localization in adult. In testicular seminiferous lobules of adult CGS, the different developmental germ cells were separated by cysts containing UCHL1 protein, but UCHL1 did not localize on the mature sperm. The results showed that extracellular UCHL1 loaded on exosomes, as a component of the homogeneous germ cell cysts, could regulate the synchronous development of sperm in testes of adult CGS.

Fighting Cancer with Mathematics and Viruses

After decades of research, oncolytic virotherapy has recently advanced to clinical application, and currently a multitude of novel agents and combination treatments are being evaluated for cancer therapy. Oncolytic agents preferentially replicate in tumor cells, inducing tumor cell lysis and complex antitumor effects, such as innate and adaptive immune responses and the destruction of tumor vasculature. With the availability of different vector platforms and the potential of both genetic engineering and combination regimens to enhance particular aspects of safety and efficacy, the identification of optimal treatments for patient subpopulations or even individual patients becomes a top priority. Mathematical modeling can provide support in this arena by making use of experimental and clinical data to generate hypotheses about the mechanisms underlying complex biology and, ultimately, predict optimal treatment protocols. Increasingly complex models can be applied to account for therapeutically relevant parameters such as components of the immune system. In this review, we describe current developments in oncolytic virotherapy and mathematical modeling to discuss the benefit of integrating different modeling approaches into biological and clinical experimentation. Conclusively, we propose a mutual combination of these research fields to increase the value of the preclinical development and the therapeutic efficacy of the resulting treatments.

Comparative microRNAome analysis of the testis and ovary of the Chinese giant salamander

MicroRNAs (miRNAs) are 18-24 nucleotides non-coding RNAs that regulate gene expression by post-transcriptional suppression of mRNA. The Chinese giant salamander (CGS, Andrias davidianus), which is an endangered species, has become one of the important models of animal evolution; however, no miRNA studies on this species have been conducted. In this study, two small RNA libraries of CGS ovary and testis were constructed using deep sequencing technology. A bioinformatics pipeline was developed to distinguish miRNA sequences from other classes of small RNAs represented in the sequencing data. We found that many miRNAs and other small RNAs such as piRNA and tsRNA were abundant in CGS tissue. A total of 757 and 756 unique miRNAs were annotated as miRNA candidates in the ovary and testis respectively. We identified 145 miRNAs in CGS ovary and 155 miRNAs in CGS testis that were homologous to those in Xenopus laevis ovary and testis respectively. Forty-five miRNAs were more highly expressed in ovary than in testis and 21 miRNAs were more highly expressed in testis than in ovary. The expression profiles of the selected miRNAs (miR-451, miR-10c, miR-101, miR-202, miR-7a and miR-499) had their own different roles in other eight tissues and different development stages of testis and ovary, suggesting that these miRNAs play vital regulatory roles in sexual differentiation, gametogenesis and development in CGS. To our knowledge, this is the first study to reveal miRNA profiles that are related to male and female CGS gonads and provide insights into sex differences in miRNA expression in CGS.