An enhancer trap in the ascidian Ciona intestinalis identifies enhancers of its Musashi orthologous gene.

The enhancer trap technique, established in Drosophila melanogaster, is a very sophisticated tool. Despite its usefulness, however, there have been very few reports on enhancer traps in other animals. The ascidian Ciona intestinalis, a splendid experimental system for developmental biology, provides good material for developmental genetics. Recently, germline transgenesis of C. intestinalis has been achieved using the Tc1/mariner superfamily transposon Minos. During the course of that study, one Minos insertion line that showed a different GFP expression pattern from other lines was isolated. One fascinating possibility is that an enhancer trap event occurred in this line. Here we show that a Minos insertion in the Ci-Musashi gene was responsible for the altered GFP expression. Ci-Musashi showed a similar expression pattern to GFP. In addition, introns of Ci-Musashi have enhancer activity that can alter the expression pattern of nearby genes to resemble that of GFP in this line. These results clearly demonstrate that an enhancer trap event that entrapped enhancers of Ci-Musashi occurred in C. intestinalis.