Transcriptional regulation of teleost Aicda genes. Part 1 – Suppressors of promiscuous promoters

In order to better understand antibody affinity maturation in fishes we sought to identify gene regulatory elements that could drive expression of activated B-cell specific fluorescent reporter transgenes in zebrafish. Specifically the promoter and several non-coding regions of the channel catfish (Ictalurus punctatus) and zebrafish (Danio rerio) were tested for transcriptional activity using a dual luciferase reporter system in transfected fish leukocytes and two mammalian cell lines that constitutively express Aicda (activation-induced cytidine deaminase). The promoters of both fish Aicda genes were as transcriptionally active as an SV40 promoter control in all cell lines tested, regardless of the cells ability to express Aicda. Coupling of a putative intron 1 enhancer or a region 10 kb upstream of the zebrafish promoter effectively silenced transcription from the fish Aicda promoter. Paradoxically these suppressor elements enhanced transcription when they were coupled to the mouse Aicda intron 1 enhancer. The results are considered in context of similar observations for Aicda transcriptional regulation in mice and in light of recent evidence that Aicda is utilized for epigenetic reprogramming of several non-lymphoid cell types.