Gene cloning and induced expression pattern of IRF4 and IRF10 in the Asian swamp eel (Monopterus albus)

Interferon regulatory factors (IRFs) are ancient molecules conserved throughout the evolution of metazoans and play a vital role in the innate and adaptive immune system (Tamura et al, 2008). To date, 11 IRF family members (IRF1-11) have been described in vertebrates and invertebrates (Huang et al, 2010), with IRF1-10 being present in most vertebrate species and IRF11 being found in non-vertebrate deuterostomes (Huang et al, 2010). Phylogenetic analysis of these 11 IRF proteins demonstrated that they can be subdivided into four groups that reflect their evolutionary history (Nehyba et al, 2009; Xu et al, 2010). Previous studies showed that in humans (Homo sapiens) and mice (Mus musculus), IRF4 was expressed in most types of immune cells, and has critical functions in B cell differentiation and immunoglobulin production (De et al, 2012). Likewise, IRF4 seems to also play important roles in the development and function of T helper cells, regulatory T (Treg) cells, dendritic cells (Xu et al, 2012) and CD4+ T cell differentiation (Suzuki et al, 2004). Other studies on chickens (Gallus gallus) found that IRF4 was mainly expressed in the bursa, bursal lymphocytes (Nehyba et al, 2002),and thymus (Dougherty et al, 2009) and it is capable of repressing the expression of ovalbumin gene (Dougherty et al, 2009). ConA can induce the expression of IRF4 in splenic cells, while IFNs cannot induce the expression of IRF4 (Nehyba et al, 2002). Furthermore, among teleost, pathogen-associated molecular patterns (PAMPs) were found to stimulate the IRF4 expression in rainbow trout (Oncorhynchus mykiss) (Holland et al, 2010) and rock bream (Oplegnathus fasciatus) (Bathige et al, 2012). Belonging to the same IRF4 subfamily, IRF10 was previously found to have been eliminated or rendered non-functional in both mice and humans (Nehyba et al, 2009). Curiously though, IRF10 can elevate the expression of major histocompatibility complex (MHC) class I molecules and guanylate-binding protein (GBP) and interfere with the induction of the type I IFN target genes in chickens (Nehyba et al, 2002). Both MHC class I and GBP play important roles in viral infections (Nehyba et al, 2002; Hu et al, 2011). Another feature of IRF10 is that similar to IRF4, it can also repress the expression of ovalbumin gene (Dougherty et al, 2009) and ConA can induce the expression of IRF10 in splenic cells (Nehyba et al, 2002). Furthermore, type I IFN and IFN-γ seem capable of inducing the expression of IRF10 in primary fibroblasts, though the expression of IRF10 is induced relatively late and needs other protein synthesis (Nehyba et al, 2002). In the Japanese flounder (Paralichthys olivaceus), bacteria or viral hemorrhagic septicemia virus (VHSV) can increase the expression of IRF10 in kidney tissue (Suzuki et al, 2011), though in zebrafish (Danio rerio) IRF10 was found to be a negative regulator of interferon transcription (Li et al, 2013). Clearly the diversity of roles and effects of IRF10 could use some clarification, especially regarding the role IRF10 plays in immune responses following viral or bacterial infections. In recent years, the Asian swamp eel (Monopterus albus) has become one of the most economically important freshwater fish in East Asia. Unfortunately, data on immune genes of M. albus are scarce as compared to other commercially important fish. Given the eels economic importance, a clearer understanding of its immune responses may help to develop strategies for disease management, which may potentially aid in aquaculture, increase yields, or decreases loses of this species. In this study, we cloned full-length cDNAs of M. albus IRF4 (maIRF4) and maIRF10 and then investigated the tissue distribution of these two genes’ expression. Paired with this analysis, we also opted to investigate a common pathogen afflicting the Asian swamp eel, Aeromonas hydrophila, the causative agent of Septicemia in this species (Yang et al, 2008; He et al, 2010). Pathogens of some disease such as stigmatosis in Asian swamp eel had not been investigated clearly. For this analysis, we measured the change in maIRF4 and maIRF10 gene expression in the head kidney (HK), spleen (SP), and gills (GI) following stimulation with PAMPs, e.g. polyinosinic: polycytidylic acid (poly I:C) and lipopolysaccharide (LPS), and a common pathogenic bacteria, A. hydrophila.