Genes expressed after retinoic acid-mediated differentiation of embryoid bodies are likely to be expressed during embryo development.

In order to test if retinoic acid-mediated differentiation of embryoid bodies can be used as an in vitro preselection method for ES cell lines generated by gene trap, we correlated gene expression after in vitro differentiation and in 11.5-day embryos. Fifty-two genes captured by gene trap and expressed in undifferentiated embryonic stem cells were analyzed. Most genes expressed after differentiation in vitro were also expressed during embryo development. In order to correlate the expression patterns in vitro and in vivo, the in vitro expression in the center and in the periphery of the embryoid body outgrowths was observed. This allowed us to distinguish, according to in vitro expression, not expressed genes from those expressed widely in 11.5-day embryos. Consequently, with this parameter we increased the probability to obtain the restricted expression patterns in vivo. This study demonstrates the potential of the differentiation procedure in combination with the gene trap to select in vitro for genes expressed during embryo development.