Artificial chromosome transgenesis reveals long-distance negative regulation of rag1 in zebrafish

Abstract

Despite the essential roles played by the recombination activating genes (rag 1 and rag2) during V(D)J recombination, the mechanisms that restrict their expression to lymphoid cells are undefined. Using a novel approach to achieve artificial chromosome transgenesis in zebrafish, we demonstrate that distal regulatory elements are critical to suppress rag 1 expression in inappropriate tissues. In contrast to smaller reporter gene constructs, 125 and 75 kb artificial chromosomes containing the zebrafish rag genomic locus directed GFP expression in a pattern reflective of endogenous rag 1. Mapping experiments identified a positive element 5' of rag 1 that enhances GFP expression in both lymphoid and non-lymphoid tissues and a negative element 5' of rag 1 that specifically suppresses GFP expression in the skeletal muscle. Our transgenic zebrafish also express GFP in olfactory neurons which we show represent an authentic rag] expression site in zebrafish.