Characterisation of the murine Hox-3.3 gene and its promoter

The murine Hox-3.3 homeobox containing gene and its Xenopus homologue (XlHbox 1) produce two embryonic transcripts from two distinct promoters located approximately 9 kb apart. In order to begin to characterise one of these promoter regions (PRII), we have sequenced 3 kb of DNA immediately upstream of the transcription start site of the PRII transcript and analyzed the sequence for sequences known to bind transcription factors. Within this region are located a number of sequences that match known cis-elements. We have analysed the ability of two of these sequences that match to the Drosophila hunchback and Antennapedia/fushi-tarazu consensus binding sequences to specifically bind proteins extracted from embryos and from adult tissues. Using gel retention assays with oligonucleotides derived from these sequences, we show that both sequences specifically bind proteins present in extracts of mouse embryos and some, but not all extracts of various adult tissues. Protein binding cannot, however, be correlated with the known spatial domains of Hox-3.3 expression, suggesting that binding to these sequences is not simply related to activation of Hox-3.3 expression. A two base pair change in the most conserved region of the hunchback-like binding sequence completely abolishes protein binding. The presence of these highly conserved cis-acting elements that are known to be involved in regulation of the hunchback, even-skipped and engrailed genes in Drosophila suggests that these sequences may also be involved in the regulation of expression of Hox-3.3 and furthermore that regulation may in part at least involve binding of hunchback-like proteins (i.e. zinc-finger proteins) and Antennapedia-like homeobox-containing proteins.