Identification and functional characterization of three irf7 transcript variants in obscure puffer (Takifugu obscurus).

Interferon regulatory factor 7 (IRF7) is a key mediator in regulating the type Ι IFN response. Although irf7 has been identified in more than twenty fish species, alternative splicing has not been found in teleost irf7. Alternative splicing is an important mechanism expanding the transcriptomic and proteomic diversity, and has been found in several IRF family members. Here, three alternative splicing variants of irf7 were identified and characterized in obscure puffer. The first splicing transcript (Toirf7v1) was predicted to encode 428 amino acids with a DNA-binding domain (DBD), an interaction-associated domain (IAD) and a serine-rich domain (SRD). Toirf7v2 encoded 430 amino acids caused by the intron retention, and contained the whole conserved domains. Toirf7v3 encoded a truncated protein with 337 amino acids resulting from the alternative 5' splice-site selection, and lacked part of IAD domain and the entire SRD domain. Functional studies demonstrated that all of the three isoforms could activate the expression of type I IFN and IFN-stimulated genes (ISGs). Nevertheless, the two variants (Toirf7v2 and Toirf7v3) exhibited much less ability to induce transcription of IFN and ISGs compared to the Toirf7v1. Our findings suggest that these splicing variants may have distinct roles in the regulation of immune response. These results will be beneficial to understand the functional characteristics of irf7 variants in fish.
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