Characterization, expression pattern and antiviral activities of oligoadenylate synthetase in Chinese Giant Salamander, Andrias davidianus

Chinese giant salamander Bcl-w: An inhibitory role in iridovirus-induced mitochondrial apoptosis and virus replication

B-cell lymphoma-2 (BCL-2) superfamily molecules play crucial roles in mitochondrial apoptosis induced by Chinese giant salamander iridovirus (GSIV). As an anti-apoptotic molecule in the BCL-2 family, the molecular mechanism of Bcl-w during GSIV infection remains unknown. In this study, we characterized for the first time an amphibian Bcl-w from Chinese giant salamander Andrias davidianus (AdBcl-w), and its function and regulatory mechanism during GSIV infection were investigated. AdBcl-w possesses the conserved structural features of Bcl-w and shares 35-54% sequence identities with other Bcl-w. mRNA expression of AdBcl-w was most abundant in liver and muscle. The AdBcl-w mRNA expression was regulated during GSIV infection. Western blotting assays revealed that the level of Bcl-w protein was downregulated markedly as the infection progresses. Confocal microscopy showed that overexpressed AdBcl-w was translocated to the mitochondria after infection with GSIV. Flow cytometry analysis demonstrated that compared with control, the apoptotic progress in cells transfected with AdBcl-w was reduced while that in cells transfected with AdBcl-w siRNA was enhanced. The number of virus major capsid protein gene copies was lower and protein synthesis was reduced in AdBcl-w overexpressing cells. In addition, AdBcl-w could bind directly to the pro-apoptotic molecule AdBak, while this interaction was weakened with GSIV infection. Moreover, p53 level was reduced and the mRNA expression levels of crucial regulatory molecules in the p53 pathway were regulated in AdBcl-w overexpressing cells during GSIV infection. These results suggested that AdBcl-w inhibit GSIV replication by regulating the virus induced mitochondrial apoptosis.

The amphibian invitrome: Past, present, and future contributions to our understanding of amphibian immunity

Many amphibian populations are declining worldwide, and infectious diseases are a leading cause. Given the eminent threat infectious diseases pose to amphibian populations, there is a need to understand the host-pathogen-environment interactions that govern amphibian susceptibility to disease and mortality events. However, using animals in research raises an ethical dilemma, which is magnified by the alarming rates at which many amphibian populations are declining. Thus, in vitro study systems such as cell lines represent valuable tools for furthering our understanding of amphibian immune systems. In this review, we curate a list of the amphibian cell lines established to date (the amphibian invitrome), highlight how research using amphibian cell lines has advanced our understanding of the amphibian immune system, anti-ranaviral defence mechanisms, and Batrachochytrium dendrobatidis replication in host cells, and offer our perspective on how future use of amphibian cell lines can advance the field of amphibian immunology.

Oral Vaccination of Largemouth Bass (Micropterus salmoides) against Largemouth Bass Ranavirus (LMBV) Using Yeast Surface Display Technology

Largemouth bass ranavirus (LMBV) infects largemouth bass, leading to significant mortality and economic losses. There are no safe and effective drugs against this disease. Oral vaccines that directly target the intestinal mucosal immune system play an important role in resisting pathogens. Herein, the B subunit of Escherichia coli heat-labile enterotoxin (LTB, a mucosal immune adjuvant) and the LMBV main capsid protein (MCP) were expressed using Saccharomyces cerevisiae surface display technology. The yeast-prepared oral vaccines were named EBY100-OMCP and EBY100-LTB-OMCP. The candidate vaccines could resist the acidic intestinal environment. After 7 days of continuous oral immunization, indicators of innate and adaptive immunity were measured on days 1, 7, 14, 21, 28, 35, and 42. High activities of immune enzymes (T-SOD, AKP, ACP, and LZM) in serum and intestinal mucus were detected. IgM in the head kidney was significantly upregulated (EBY100-OMCP group: 3.8-fold; BY100-LTB-OMCP group: 4.3-fold). IgT was upregulated in the intestines (EBY100-OMCP group: 5.6-fold; EBY100-LTB-OMCP group: 6.7-fold). Serum neutralizing antibody titers of the two groups reached 1:85. Oral vaccination protected against LMBV infection. The relative percent survival was 52.1% (EBY100-OMCP) and 66.7% (EBY100-LTB-OMCP). Thus, EBY100-OMCP and EBY100-LTB-OMCP are promising and effective candidate vaccines against LMBV infection.

Glycosylphosphatidylinositol Mannosyltransferase Ⅰ Protects Chinese Giant Salamander, Andrias davidianus, against Iridovirus

Glycosylphosphatidylinositol mannosyltransferase I (GPI-MT-I) is an essential glycosyltransferase of glycosylphosphatidylinositol-anchor proteins (GPI-APs) that transfers the first of the four mannoses in GPI-AP precursors, which have multiple functions, including immune response and signal transduction. In this study, the GPI-MT-I gene that regulates GPI-AP biosynthesis in Andrias davidianus (AdGPI-MT-I) was characterized for the first time. The open reading frame (ORF) of AdGPI-MT-I is 1293 bp and encodes a protein of 430 amino acids that contains a conserved PMT2 superfamily domain. AdGPI-MT-I mRNA was widely expressed in the tissues of the Chinese giant salamander. The mRNA expression level of AdGPI-MT-I in the spleen, kidney, and muscle cell line (GSM cells) was significantly upregulated post Chinese giant salamander iridovirus (GSIV) infection. The mRNA expression of the virus major capsid protein (MCP) in AdGPI-MT-I-overexpressed cells was significantly reduced. Moreover, a lower level of virus MCP synthesis and gene copying in AdGPI-MT-I-overexpressed cells was confirmed by western blot and ddPCR. These results collectively suggest that GSIV replication in GSM cells was significantly reduced by the overexpression of the AdGPI-MT-I protein, which may contribute to a better understanding of the antiviral mechanism against iridovirus infection.