Cloning and characterization of two genes encoding rainbow trout homologues of the IFITM protein family

To identify genes connected with leucocyte function in rainbow trout a cDNA library derived from head kidney leucocytes exposed to phytohemagglutinin (PHA) was screened. A clone with homology to the previously described human interferon-inducible transmembrane proteins (IFITM) was isolated. This clone was used to screen a trout genomic library identifying two trout IFITM genes. Both genes are composed of two exons, in common with human IFITM genes. The promoter regions of both genes were examined and found to contain interferon, immune and stress-related transcription factor binding sites. Transcripts for both genes were found in most tissues examined. Trout IFITM1 mRNA levels were highest in head kidney, but present in all tissues studied. IFITM2 mRNA levels were highest in gill, heart and liver, and absent in head kidney and blood. In response to conditions mimicking viral infection, transcription of the trout IFITM genes was elevated in a trout spleen macrophage cell line (RTS11) over the examined timecourse (72 h). This study suggests that the organization and transcription of the IFITM genes is well conserved between human and rainbow trout.