Identification of Two Subgroups of Type I IFNs in Perciforme Fish Large Yellow Croaker Larimichthys crocea Provides Novel Insights into Function and Regulation of Fish Type I IFNs

Abstract

Like mammals, fish possess an interferon regulatory factor (IRF) 3/IRF7-dependent type I IFN responses, but the exact mechanism by which IRF3/IRF7 regulate the type I IFNs remains largely unknown. In this study, we identified two type I IFNs in the Perciforme fish large yellow croaker Larimichthys crocea, one of which belongs to the fish IFNd subgroup and the other is assigned to a novel subgroup of group I IFNs in fish, tentatively termed IFNh. The two IFN genes are constitutively expressed in all examined tissues, but with varied expression levels. Both IFN genes can be rapidly induced in head kidney and spleen tissues by polyinosinic–polycytidylic acid. The recombinant IFNh was shown to be more potent to trigger a rapid induction of the antiviral genes MxA and protein kinase R than the IFNd, suggesting that they may play distinct roles in regulating early antiviral immunity. Strikingly, IFNd, but not IFNh, could induce the gene expression of itself and IFNh through a positive feedback loop mediated by the IFNd-dependent activation of IRF3 and IRF7. Furthermore, our data demonstrate that the induction of IFNd can be enhanced by the dimeric formation of IRF3 and IRF7, while the IFNh expression mainly involves IRF3. Taken together, our findings demonstrate that the IFN responses are diverse in fish and are likely to be regulated by distinct mechanisms.

The Peculiar Characteristics of Fish Type I Interferons

“…In turbot, injection of a plasmid expressing IFN1 (group II), but not of a plasmid expressing IFN2 (group I), led to induction of typical ISG and protection against VHSV infection [17]. Overall, the large diversity of perciforms has not been well explored yet; interestingly, a recent report in the yellow croaker confirmed that the distinction between group I and group II IFN also hold for this vast group [48], although genome contraction as in tetraodontiforms, or additional duplications, certainly led to large variations of the repertoire.…”

The discovery and comparative expression analysis of three distinct type I interferons in the perciform fish, meagre (Argyrosomus regius)

“…IFNh is produced in response to poly I:C stimulation and the recombinant protein induces the expression of ISGs such as Mx and PKR (as well as itself) and has anti-viral activity. However, it does not induce the expression or phosphorylation of IRF3 or IRF7 and it has been hypothesised that downstream signalling may occur solely through the Jak-STAT pathway (Ding et al, 2016). Further analysis of IFN2 from turbot reveals it is in fact an IFNh, confirming this subgroup is more widely present in Acanthopterygian species.…”

“…Intriguingly IFN2, unlike IFN1, was not able to induce protection when administered prior to VHSV infection and this was linked to a lack of induction of a number of ISGs (eg Mx, ifi56, isg15), but it could induce IL-1β expression. More recently a new IFN subgroup, IFNh, has been identified in large yellow croaker (Larimichthys crocea) and in various other perciform species (Ding et al, 2016). IFNh is produced in response to poly I:C stimulation and the recombinant protein induces the expression of ISGs such as Mx and PKR (as well as itself) and has anti-viral activity.…”

Functional Analysis of IRF1 Reveals its Role in the Activation of the Type I IFN Pathway in Golden Pompano, Trachinotus ovatus (Linnaeus 1758)

“…Then, the total protein was electrophoresed on 12% SDS-PAGE and electrophoretically transferred to polyvinylidene fluoride (PVDF) membranes (Millipore, USA) using the PierceG2 Fast Blotter (25 V for 10 min, Pierce, Rockford, IL, USA). Western blotting (WB) analyses were carried out according to a previously described protocol [25].…”

“…Type I IFNs contain two cysteine residues in all teleost fish lineages; nevertheless, type II IFNs include four cysteine residues in only a few species [19][20][21][22]. The transcriptional activation of type I and II IFNs is regulated by IRFs in both vertebrates and invertebrates [23][24][25]. In mammals, IRF1 was first discovered to bind and activate the IFNβ promoter [26].…”