Identification and functional analysis of interferon regulatory factor 3 in Lateolabrax maculatus

The fusion gene hsf5-rnf43 in Nile tilapia: A potential regulator in the maintenance of testis function and sexual differentiation

We identified that the genes heat shock transcription factor 5 (hsf5) and ring finger protein 43 (rnf43) happened fusion in Nile tilapia (Oreochromis niloticus), called hsf5-rnf43, and provided the characteristic and functional analysis of hsf5-rnf43 gene in fish for the first time. Analysis of spatiotemporal expression showed that hsf5-rnf43 was specifically expressed in the testis and located in primary spermatocytes of adult Nile tilapia and gradually increased during testis development from 5 to 180 days after hatching. We also found DNA methylation regulated sex-biased expression of hsf5-rnf43 in the early development of Nile tilapia, and was affected by high temperature during the thermosensitive period of Nile tilapia sex differentiation. Therefore, we first reported that the fusion gene hsf5-rnf43 was sex-biased expressed in the testis regulated by DNA methylation and affected by high temperature, which may be involved in the maintenance of testis function and sex differentiation of Nile tilapia.

Effect of CRISPR/Cas9-mediated knockout of either IRF-3 or IRF-5 gene in Epithelioma papulosum cyprini cells on type I interferon response and NF-κB activity

Transcription factors related to the activation of type I interferons (IFNs) and nuclear factor-kappa B (NF-κB) are known to be critical in innate immune responses. Interferon regulatory factors (IRFs) are a family of transcription factors. IRF-3 is known to act as the primary regulator in type I IFN signaling in response to viral infections, and the upregulation of IRF5 by virus infection has been reported in various fish species. One of the ways to know the functional role of certain genes is the production of target gene(s) knockout cells or organisms. In the present study, we produced either IRF3 or IRF5 gene knockout Epithelioma papulosum cyprini (EPC) cells using a CRISPR/Cas9 system, and investigated the effect of IRF3 gene and IRF5 gene knockout on polyinosinic:polycytidylic acid (ploly (I:C))-mediated and viral hemorrhagic septicemia virus (VHSV) infection-mediated type I IFN response and NF-κB activation. Both IRF3 knockout and IRF5 knockout EPC cells showed severely decreased type I IFN responses measured by ISRE activity and the expression of Mx1 and ISG15 genes when stimulated with poly (I:C), while the decreased level of type I IFN responses was not high as by poly (I:C) stimulation when infected with VHSV. Different from type I IFN response, NF-κB activities in IRF3 and IRF5 knockout cells were not highly different between poly (I:C) stimulated cells and VHSV-infected cells. Further studies are needed to elucidate pathways responsible for the type I IFN responses and NF-κB activation by VHSV infection.

Identification and functional analysis of two interferon regulatory factor 3 genes and their involvement in antiviral immune responses in the Chinese giant salamander Andrias davidianus

Interferon regulatory factor 3 (IRF3), a crucial member of interferon regulatory factor (IRF) family, plays an important role in innate immunity in vertebrates. However, there are no reports on the characterization and especially their respective functional analysis of two IRF3 genes in some species. In this study, two IRF3 genes as well as their roles in the immune response were identified and investigated in Chinese giant salamander, Andrias davidianus. The complete open reading frames of AdIRF3A and AdIRF3B were 1, 113 bp and 1, 380 bp in length, encoding 370 and 459 amino acids, respectively. Both AdIRF3A and AdIRF3B protein contain an IRF and an IRF3 domain. Phylogenetic analysis indicated that AdIRF3s clustered together with other IRF3 proteins. Tissue distribution analysis showed that AdIRF3s were expressed in all tissues tested, with highest expression levels in blood. Both AdIRF3s actively responded to Chinese giant salamander iridovirus (GSIV) and poly (I:C) challenge in A. davidianus. AdIRF3A/B silencing significantly suppressed the DNA virus and viral RNA analog-induced expression of IFN-inducible genes. Luciferase reporter assay further confirmed the regulatory role of AdIRF3s in IFN signaling. These results provide new insights into the origin or evolution of IRF3 in amphibians and even in vertebrates.

Expression and DNA methylation analysis of cyp19a1a in Chinese sea perch Lateolabrax maculatus

Cytochrome P450 aromatase (P450arom), which is encoded by cyp19a1a, can convert androgen to estrogen. Therefore, P450arom is important in gonadal differentiation and maintenance. In this study, we analyzed the expression and DNA methylation of cyp19a from Chinese sea perch Lateolabrax maculatus (sp. cyp19a1a). The sp. cyp19a1a gene consists of 9 exons, but only 3.5 kb, being smaller than the human cyp19a1a, as a result of small introns. The sp. cyp19a1a protein contains 518 amino acid residues and evolutionarily conserved domains and is clustered in the teleost subfamily on the phylogenetic tree. Amino acid alignment indicates that sp. cyp19a1a shares the highest identity (91.6%) to Epinephelus akaara and Lates calcarifer. Endogenous sp. cyp19a1a is detected mainly in stromal cells around the oocytes of stage I ovary, and the gene expression level has no difference after 40 days fresh water culture in both ovary and testis. The sp. Cyp19a1a can catalyze the production of estrogen from androgen in vitro. Seven CpG dinucleotides are found in the proximal promoter. Binding sites of the conserved predicted transcription factors include cAMP response element, steroidogenic factor-1, and SRY-Box. The deletion of this region reduces promoter activity significantly. The methylation level of the seven CpG dinucleotides in cyp19a1a promoter is higher in the testis (44.25 ± 4.04) than in the ovary (24.71 ± 3.05). The induced hypermethylation of the sp. cyp19a1a promoter suppressed promoter transcription function in vitro. These results suggest that DNA methylation may be a mechanism used for natural sex maintenance.

Sequence and functional analysis of intestinal alkaline phosphatase from Lateolabrax maculatus

Alkaline phosphatases (Alps) belong to a class of phosphate transferases that dephosphorylate lipopolysaccharide (LPS), adenosine triphosphate, and nucleotides. In this study, a 1874-base pair (bp) intestinal alp cDNA sequence was cloned from Lateolabrax maculatus and designated as Lm-alpi. It contained a 1611 bp open reading frame which encoded a protein with 537 amino acids. Protein sequence alignment showed that Lm-AlpI shared 29.8-79.8% identity with its homologs. Lm-AlpI catalytic sites contained three metal ion sites (two Zn²⁺ and one Mg²⁺), referring to D73, H184, D348, H349, H352, H464, D389, and H390 residues, which are essential for enzymatic activity and conservation in different organisms. Two predicted disulfide bonds in Lm-AlpI were composed of four cysteines (C152-C214 and C499-C506), which were homologous to those of mammals. Immunohistochemical staining revealed that Lm-AlpI was mainly expressed on the mucosal surface of the gastrointestinal tract, including stomach, intestine, and gastric cecum. Lm-AlpI was mainly located on the plasma membrane of transiently transfected HeLa cells. The mRNA of Lm-alpi was mainly expressed in the intestine, and its expression levels gradually increased after LPS treatment and further increased by 1.81-fold after 48 h. After desalting culture, the relative mRNA expression level of Lm-alpi decreased at 30 and 50 days after hatching (DAH) and then returned to normal levels at 70 DAH. Further experiments demonstrated that the enzyme activity of Lm-AlpI exhibited an expression pattern similar to that of the mRNA expression of Lm-alpi after LPS treatment and desalting culture. This study provided valuable information on the Lm-AlpI functions associated with the mucosal immunity and salinity adaptation of L. maculatus.