Grass carp reovirus (GCRV) causes severe hemorrhagic disease in farmed grass carp, yet how GCRV exploits host membrane remodeling machinery to support replication remains poorly defined. Here, we identified grass carp atlastin-1 (gcATL1), an endoplasmic reticulum (ER) membrane-fusion GTPase, as a pro-viral host factor for GCRV infection. Structural and phylogenetic analyses confirmed that gcATL1 harbors conserved domains typical of vertebrate ATL1 orthologs. Transcriptional profiling revealed broad tissue distribution of gcATL1 and significant transcriptional induction in brain upon GCRV challenge. gcATL1 localized to the ER. Functional assays showed that gcATL1 overexpression enhanced GCRV propagation, accompanied by elevated viral titers, increased viral protein abundance, and aggravated cytopathic effects. Furthermore, overexpression of gcATL1 promoted viral inclusion bodies (VIBs) biogenesis, accompanied by progressively increased ER-VIB colocalization in a GBP-domain-dependent manner. Mechanistically, gcATL1 interacted with viral NS80 via its conserved GBP domain to facilitate viral replication. Meanwhile, gcATL1 disrupted cellular redox homeostasis and exacerbated virus-elicited oxidative stress injury. Collectively, our results reveal that GCRV hijacks gcATL1 to promote infection through coordinating viral protein interaction and host stress responses, offering novel insights into the involvement of host GTPase in aquatic reovirus pathogenesis.
Streptococcus iniae is a major bacterial pathogen causing severe economic losses in marine and freshwater aquaculture worldwide. This study evaluated the long-term protective efficacy and immunostimulatory effects of a formalin-killed cell (FKC) vaccine, with and without Montanide ISA 763 adjuvant, against S. iniae infection in four-finger threadfin (Eleutheronema tetradactylum). Fish were assigned to three groups: control, FKC, and FKC combined with Montanide ISA 763 (FKC + ISA). Vaccinated fish received 1.5 × 109 CFU/fish and were challenged at 1, 3, and 6 months post-vaccination (mpv) using the virulent S. iniae GSI-111 strain. An additional heterologous challenge using the S. iniae T6 strain was performed at 6 mpv. Immune-related gene expression, including complement component 2 (C2), cluster of differentiation 8, tumor necrosis factor-α, interleukin-10, and interleukin-12 in spleen and kidney tissues, as well as serum lysozyme activity and S. iniae-specific immunoglobulin M (IgM) antibody responses, were evaluated throughout the experimental period. Both vaccinated groups exhibited significantly stronger immune responses than the control group, with the FKC + ISA group demonstrating the greatest and most sustained immunological activation. Elevated serum lysozyme activity and specific IgM antibody levels were maintained for up to 6 mpv. Following homologous challenge with the GSI-111 strain, the FKC + ISA group achieved 100% relative percent survival (RPS) under the present experimental conditions at all challenge time points, whereas the FKC group provided consistently high but slightly lower protection (92.9–97.2% RPS). During the heterologous challenge with the T6 strain at 6 mpv, the FKC + ISA group again achieved 100% RPS under the present experimental conditions, while the FKC group achieved 78.6% RPS. In contrast, the control group experienced high mortality, with survival rates ranging from 50 to 75%. Re-isolation analysis confirmed the absence or marked reduction of S. iniae in surviving vaccinated fish. These findings demonstrate that the Montanide ISA 763-adjuvanted FKC vaccine elicits robust and durable humoral and cellular immune responses, providing long-term homologous and heterologous protection against S. iniae infection in four-finger threadfin.
DExD/H-box RNA helicases are multifunctional regulators of RNA metabolism and some are associated with host defence against viruses. However, the in vivo roles of individual family members remain insufficiently characterised. Ddx1 is one such example, implicated in antiviral signalling as well as in the replication of several viruses. In this study, we investigated the function of Ddx1 during vertebrate development and viral infection in zebrafish (Danio rerio) model using both loss-of-function and gain-of-function approaches. CRISPR/Cas9-mediated knockout of ddx1 resulted in viable embryos and larvae without overt developmental abnormalities; however, knockouts failed to survive to adulthood, indicating that Ddx1 is required for later stages of development. To assess its role in antiviral defence, ddx1 knockout and wild-type larvae were experimentally infected with tilapia lake virus (TiLV), a virus known to induce a strong type I interferon response in zebrafish. Survival rates, viral loads, and expression of selected type I interferon pathway genes (rig-I, ifnφ1, mxa) were comparable between genotypes, demonstrating that Ddx1 is not essential for the larval antiviral response to TiLV. Consistently, overexpression of ddx1 did not enhance resistance to infection. Together, these findings indicate that while Ddx1 is critical for zebrafish survival to adulthood, it does not play a measurable role in early antiviral immunity against TiLV in zebrafish larvae.
