Identification of immune-responsive circular RNAs in shrimp (Litopenaeus vannamei) upon yellow head virus infection

Circular RNAs (circRNAs) are a subclass of non-coding RNAs (ncRNAs) formed through a process known as back-splicing. They play a crucial role in the genetic regulation of various biological processes. Currently, circRNAs have been identified as participants in the antiviral response within mammalian cells. However, circRNAs in shrimp infected with the yellow head virus (YHV) remain largely unexplored. Therefore, this study aims to identify circRNAs in the hemocytes of Litopenaeus vannamei during YHV infection. We discovered 358 differentially expressed circRNAs (DECs), with 177 of them being up-regulated and 181 down-regulated. Subsequently, eight DECs, including circ_alpha-1-inhibitor 3, circ_CDC42 small effector protein 2, circ_hemicentin 2, circ_integrin alpha V, circ_kazal-type proteinase inhibitor, circ_phenoloxidase 3, circ_related protein rab-8B, and circ_protein toll-like, were randomly selected for analysis of their expression patterns during YHV infection using qRT-PCR. Furthermore, the circRNAs' characteristics were confirmed through PCR, RNase R treatment, and Sanger sequencing, all of which were consistent with the features of circRNAs. These findings contribute to a better understanding of circRNAs' involvement in the antiviral response in shrimp.

Caspase-3, a shrimp phosphorylated hemocytic protein is necessary to control YHV infection

By using immunohistochemistry detection, yellow head virus (YHV) was found to replicate in granule-containing hemocytes including semi-granular hemocytes (SGC) and granular hemocytes (GC) during the early phase (24 h post injection) of YHV-infected shrimp. Higher signal of YHV infection was found in GC more than in SGC. Comparative phosphoproteomic profiles between YHV-infected and non-infected GC reveal a number of phosphoproteins with different expression levels. The phosphoprotein spot with later on identified as caspase-3 in YHV-infected GC is most interesting. Blocking caspase-3 function using a specific inhibitor (Ac-DEVD-CMK) demonstrated high replication of YHV and consequently, high shrimp mortality. The immunohistochemistry results confirmed the high viral load in shrimp that caspase-3 activity was blocked. Caspase-3 is regulated through a variety of posttranslational modifications, including phosphorylation. Analysis of phosphorylation sites of shrimp caspase-3 revealed phosphorylation sites at serine residue. Taken together, caspase-3 is a hemocytic protein isolated from shrimp granular hemocytes with a role in anti-YHV response and regulated through the phosphorylation process.

Yellow head virus infection in black tiger shrimp reveals specific interaction with granule-containing hemocytes and crustinPm1 as a responsive protein

Yellow head virus (YHV) causes acute infections and mass mortality in black tiger shrimp culture. Our study aims to investigate molecular interaction between YHV and circulating hemocytes of Penaeus monodon at early infection. Total shrimp hemocytes were isolated by Percoll gradient centrifugation and identified by flow cytometric analysis. At least three types of hemocyte cells were identified as hyaline, semi-granular, and granular hemocytes. Experimental infection of YHV in shrimp culture demonstrated drastic changes in total and each hemocyte cell counts. Immunohistochemistry analysis demonstrated interaction and replication of YHV mainly with the granule-containing hemocytes and little to none in hyaline cell. These granule-containing hemocytes are proposed to be YHV targets providing the first line of defense to viral infection. Protein expression profiling of granule-containing hemocytes revealed several immune-responsive proteins including antimicrobial protein crustins (crustinPm1 and crustinPm4), alpha-2-macroglobulin, and kazal-type serine proteinase inhibitor. During an early phase of YHV infection at 6 hpi crustinPm1 illustrated a significant increase of mRNA and protein expression level in plasma. The results suggest that an antimicrobial crustinPm1 may participate in shrimp defense mechanism against YHV, especially on the granule-containing hemocytes.

A novel lectin domain-containing protein (LvCTLD) associated with response of the whiteleg shrimp Penaeus (Litopenaeus) vannamei to yellow head virus (YHV)

When using mRNA from gills of normal whiteleg shrimp Penaeus (Litopenaeus) vannamei as the tester and mRNA from yellow head virus (YHV)-infected shrimp as the driver, subtractive suppression hybridization (SSH) revealed that a novel EST clone of 198 bp with a putative C-type lectin-like domain (CTLD) was downregulated in YHV-infected shrimp. The clone nucleotide sequence had 99% identity with one contig MGID1052359 (1,380 bp) reported in an EST database of P. vannamei, and the presence of this target in normal shrimp was confirmed by RT-PCR using primers designed from the MGID1052359 sequence. Analysis of the primary structure of the deduced amino acid (a.a.) sequence of the contig revealed a short portion (40 a.a. residues) at its N-terminus with high similarity to a low density lipoprotein receptor (LDLR) class A domain and another 152 a.a. residues at its C-terminus with high similarity to a C-type lectin domain. Thus, the clone was named LvCTLD and three recombinant proteins (LvCTLD, the LDLR domain and the CTLD domain) were synthesized in a bacterial system based on its sequence. An in vitro encapsulation assay revealed that Sepharose 4B beads coated with rLvCTLD were encapsulated by shrimp hemocytes and that melanization followed by 24 h post-encapsulation. The encapsulation activity of rLvCTLD was inhibited by 100 mM galactose, but not mannose or EDTA. In vivo injection of rLvCTLD or rLvCTLD plus YHV resulted in a significant elevation of PO activity in the hemolymph of the challenged shrimp when compared to shrimp injected with buffer, suggesting that rLvCTLD could activate the proPO system. An ELISA test revealed that rLvCTLD could bind to YHV particles in the presence of shrimp hemolymph. Phylogenetic analysis suggested that the LvCTLD sequence was more closely related to an antiviral gene found in Penaeus monodon (PmAV) than to other reported shrimp lectins. Taken together, we conclude that a novel shrimp LvCTLD is a host recognition molecule involved in the shrimp defense mechanism against YHV via recruitment of hemocytes, probably at the site of viral infection, and via activation of the proPO system.

Application of YHV-protease dsRNA for protection and therapeutic treatment against yellow head virus infection in Litopenaeus vannamei

While farming of the Pacific white shrimp Litopenaeus vannamei is well established in North and South America, the industry has more recently been introduced to Asia, and the Pacific white shrimp is now the most commonly farmed species in Thailand. However, outbreaks of yellow head virus (YHV) disease in the Pacific white shrimp have caused severe economic losses and currently there is no effective prevention or treatment of YHV infections. The YHV-protease double-stranded RNA (YHV-Pro dsRNA) can act as both a prophylactic agent and as a treatment to inhibit YHV replication in infected black tiger shrimp Penaeus monodon. The utility of this methodology to other shrimp species has not, however, been established. The purpose of this study was to determine whether YHV-Pro dsRNA can be applied to the Pacific white shrimp. To assess prophylactic efficiency, YHV-Pro dsRNA was injected into juvenile shrimp 24 h prior to challenge with YHV. Subsequent YHV replication was inhibited by YHV-Pro dsRNA as compared with injection of an unrelated dsRNA. For therapeutic treatment of YHV-infected shrimp, shrimp were challenged with YHV before dsRNA injection. Injection of YHV-Pro dsRNA up to 6 h post-infection resulted in the almost complete elimination of YHV replication. These results suggest that YHV-Pro dsRNA can also be broadly applied as a prophylactic agent to inhibit YHV replication and therapeutic treatment of YHV-infected Pacific white shrimp.

Changes in the histological organization and spheroid formation in lymphoid organ of Penaeus monodon infected with yellow head virus

The changes in the histological and three dimensional organizations of lymphoid organ and characteristics of lymphoid cells after chronic infection with yellow head virus (YHV) in Penaeus monodon were investigated. The vascular cast of infected lymphoid organ showed less branching and dramatically shortened terminal capillaries that formed the lymphoid tubules, and only large stumps of these lymphoid tubules remained. This might occur because the terminal ends of the tubules were damaged from YHV infection, as stromal cells and hemocytes in the LT wall were infected and formed foci that could give rise to lymphoid spheroids that broke away from the original lymphoid tubules. Histologically, there was a decrease of PAS-stained connective tissue materials in lymphoid spheroids as well as a decrease of stromal cells as marked by anti-vimentin antibody. This indicated that stromal cells together with type 1 fibers and associated extracellular matrix degenerated in lymphoid spheroids, while type 2 or reticular fibers proliferated and encapsulated the spheroids.