An enhancer sequence directs LacZ expression to developing pharyngeal endoderm in transgenic mice.

The murine Hoxc-6 homeobox gene comprises three exons with two distinct promoters (PRI and PRII) located 9 kb apart. To characterise the PRII promoter, a region 3 kb upstream of the transcription start site was sequenced, and an Antananapedia-like consensus binding sequence was found (Coletta et al., 1991). A LacZ reporter gene construct, containing three copies of this sequence, directs highly specific expression in cells forming pharyngeal endoderm in transgenic mice. Expression was first detected in a few individual anterior endoderm cells at E7.5, which increase in number up to E9.5, where expression was clearly visible in the pharyngeal endoderm. Expression of the endodermal genes HNF3beta, Pax-9, Shh, and Nkx2.5 showed colocalization with the LacZ-positive cells in the foregut and pharyngeal endoderm. This novel enhancer provides a means of tracking the morphogenetic movement of endodermal cells fated to form the foregut.