Molecular cloning and characterization of rainbow trout (Oncorhynchus mykiss) CCAAT/enhancer binding protein ?

A full-length cDNA encoding CCAAT/enhancer-binding protein β (C/EBPβ) was cloned from rainbow trout by anchored PCR. The putative 291 amino acid protein has 53% and 32% identity to the zebrafish and Japanese flounder sequences, respectively, and 30-34% identity to tetrapod homologues. This clone contains most conserved C/EBPβ domains except the second transactivation domain just like the zebrafish homologue. Also similar to zebrafish, rainbow trout produces only shorter C/EBPβ isoforms (LAP and LIP) but not the longer isoform (LAP*). However, unlike the zebrafish and Japanese flounder homologues, trout C/EBPβ has the short open reading frame (uORF) upstream of the start codon for LAP but in an alternate reading frame, a feature of tetrapod C/EBPβ genes. In normal rainbow trout, C/EBPβ mRNA was detected in peripheral blood leukocytes, head kidney, posterior kidney, liver, spleen, gills, intestine and muscle. RT-PCR revealed that transcript levels of trout C/EBPβ are clearly higher in sodium alginate-induced peritoneal cells than in head kidney and peritoneal cells of saline-injected fish or head kidney cells of alginate-injected fish. Together with expression in immunologically important tissues, this indicates that C/EBPβ is likely to be involved in the immune response just as in mammals. Southern hybridization suggested that C/EBPβ is a single copy gene. There are no introns in this C/EBPβ gene, just like the mammalian homologues. These data suggest that we have obtained the trout ortholog of C/EBPβ.[PUBLICATION ABSTRACT]