DETECTION OF TARGETED GFP-HOX GENE FUSIONS DURING MOUSE EMBRYOGENESIS

The ability to use a vital cell marker to study mouse embryogenesis wi ll open new avenues of experimental research. Recently, the use of tra nsgenic mice, containing multiple copies of the jellyfish gene encodin g the green fluorescent protein (GFP), has begun to realize this poten tial. Here, we show that the fluorescent signals produced by single-co py, targeted GFP in-frame fusions with two different murine Hox genes, Hoxa1 and Hoxc13, are readily detectable by using confocal microscopy . Since Hoxa1 is expressed early and Hoxc13 is expressed late in mouse embryogenesis, this study shows that single-copy GFP gene fusions can be used through most of mouse embryogenesis. Previously, targeted lac Z gene fusions have been very useful for analyzing mouse mutants. Use of GFP gene fusions extends the benefits of targeted lacZ gene fusions by providing the additional utility of a vital marker. Our analysis o f the Hoxc13(GFPneo) embryos reveals GFP expression in each of the sit es expected from analysis of Hoxc13(lacZneo) embryos. Similarly, Hoxa1 (GFPneo) expression was detected in all of the sites predicted from RN A in situ analysis. GFP expression in the foregut pocket of Hoxa1(GFPn eo) embryos suggests a role for Hoxa1 in foregut-mediated differentiat ion of the cardiogenic mesoderm.