Pathogenicity of Aeromonas veronii Isolated from Diseased Macrobrachium rosenbergii and Host Immune-Related Gene Expression Profiles.

Aeromonas veronii is widespread in aquatic environments and is responsible for infecting various aquatic animals. In this study, a dominant strain was isolated from the hepatopancreas of diseased Macrobrachium rosenbergii and was named JDM1-1. According to its morphological, physiological, and biochemical characteristics and molecular identification, isolate JDM1-1 was identified as A. veronii. The results of artificial challenge showed isolate JDM1-1 had high pathogenicity to M. rosenbergii with an LD50 value of 8.35 × 105 CFU/mL during the challenge test. Histopathological analysis revealed severe damage in the hepatopancreas and gills of the diseased prawns, characterized by the enlargement of the hepatic tubule lumen and gaps between the tubules as well as clubbing and degeneration observed at the distal end of the gill filament. Eight virulence-related genes, namely aer, ompA, lip, tapA, hlyA, flgA, flgM, and flgN, were screened by PCR assay. In addition, virulence factor detection showed that the JDM1-1 isolate produced lipase, lecithinase, gelatinase, and hemolysin. Furthermore, the mRNA expression profiles of immune-related genes of M. rosenbergii following A. veronii infection, including ALF1, ALF2, Crustin, C-lectin, and Lysozyme, were assessed, and the results revealed a significant upregulation in the hepatopancreas and intestines at different hours post infection. This study demonstrates that A. veronii is a causative agent associated with massive die-offs of M. rosenbergii and contributes valuable insights into the pathogenesis and host defense mechanisms of A. veronii invasion.

rpoS involved in immune response of Macrobrachium nipponens to Vibrio mimicus infection.

Vibrio mimicus is a pathogenic bacterium that cause red body disease in Macrobrachium nipponense, leading to high mortality and financial loss. Based on previous studies, rpoS gene contribute to bacterial pathogenicity during infection, but the role of RpoS involved in the immune response of M. nipponense under V. mimicus infection remains unclear. In this study, the pathogen load and the RNA-seq of M. nipponense under wild-type and ΔrpoS strain V. mimicus infection were investigated. Over the entire infection period, the ΔrpoS strain pathogen load was always lower than that of the wild-type strain in the M. nipponense hemolymph, hepatopancreas, gill and muscle. Furthermore, the expression level of rpoS gene in the hepatopancreas was the highest at 24 hours post infection (hpi), then the samples of hepatopancreas tissue infected with the wild type and ΔrpoS strain at 24 hpi were selected for RNA-seq sequencing. The results revealed a significant change in the transcriptomes of the hepatopancreases infected with ΔrpoS strain. In contrast to the wild-type infected group, the ΔrpoS strain infected group exhibited differentially expressed genes (DEGs) enriched in 181 KEGG pathways at 24 hpi. Among these pathways, 8 immune system-related pathways were enriched, including ECM-receptor interaction, PI3K-Akt signaling pathway, Rap1 signaling pathway, Gap junction, and Focal adhesion, etc. Among these pathways, up-regulated genes related to Kazal-type serine protease inhibitors, S-antigen protein, copper zinc superoxide dismutase, tight junction protein, etc. were enriched. This study elucidates that rpoS can affect tissue bacterial load and immune-related pathways, thereby impacting the survival rate of M. nipponense under V. mimicus infection. These findings validate the potential of rpoS as a promising target for the development of a live attenuated vaccine against V. mimicus.

Isolation and the pathogenicity characterization of Decapod iridescent virus 1 (DIV1) from diseased Macrobrachium nipponense and its activation on host immune response.

The high morbidity and mortality of Macrobrachium nipponense occurred in several farms in China, with cardinal symptoms of slow swimming, loss of appetite, empty of intestine, reddening of the hepatopancreas and gills. The pathogen has been confirmed as Decapod Iridescent Virus 1 (DIV1), namely DIV1-mn, by molecular epidemiology, histopathological examination, TEM observation, challenge experiment, and viral load detection. Histopathological analysis showed severe damage in hepatopancreas and gills of diseased prawns, exhibited few eosinophilic inclusions and pyknosis, and TEM of diseased prawns revealed that icosahedral virus particles existed in hepatopancreas and gill, which confirmed the disease of the farmed prawns caused by the DIV1 infection. Besides, challenge tests showed LD50 of DIV1 to M. nipponense was determined to be 2.14 × 104 copies/mL, and real-time PCR revealed that M. nipponense had a very high DIV1 load in the hemocytes, gills and hepatopancreas after infection. Furthermore, qRT-PCR was undertaken to investigated the expression of six immune-related genes in DIV1-infected M. nipponense after different time points, and the results revealed UCHL3, Relish, Gly-Cru2, CTL, MyD88 and Hemocyanin were significantly up-regulated in hemocytes, gills and hepatopancreas, which revealed various expression patterns in response to DIV1 infection. This study revealed that DIV1 infection is responsible for the mass mortality of M. nipponense, one of the important crustacean species, indicating its high susceptibility to DIV1. Moreover, this study will contribute to exploring the interaction between the host and DIV1 infection, specifically in terms of understanding how M. nipponense recognizes and eliminates the invading of DIV1.

DNA/RNA helicase DHX36 is required for late stages of spermatogenesis.

Spermatogenesis is a highly complex developmental process that typically consists of mitosis, meiosis, and spermiogenesis. DNA/RNA helicase DHX36, a unique guanine-quadruplex (G4) resolvase, plays crucial roles in a variety of biological processes. We previously showed that DHX36 is highly expressed in male germ cells with the highest level in zygotene spermatocytes. Here, we deleted Dhx36 in advanced germ cells with Stra8-GFPCre and found that a Dhx36 deficiency in the differentiated spermatogonia leads to meiotic defects and abnormal spermiogenesis. These defects in late stages of spermatogenesis arise from dysregulated transcription of G4-harboring genes, which are required for meiosis. Thus, this study reveals that Dhx36 plays crucial roles in late stages of spermatogenesis.