Characterization of a functional promoter for the Xenopus wnt-1 gene on vivo

The Xenopus homolog of the proto-oncogene wnt-1 (int-1) is transiently expressed during neurula and tailbud stages of early development. To determine the mechanisms involved in the transcriptional regulation of the Xwnt-1 gene, we isolated Xwnt-1 genomic sequences. The promoter activity of the 5' flanking region of the gene was analysed by microinjection of chimeric luciferase reporter constructs into embryos. It is shown that the proximal 220 bp of the Xwnt-1 promoter is able to confer activation of the reporter gene at the early neurula stage. DNaseI footprinting analysis of the proximal promoter region with nuclear protein extracts from neurula stage embryos revealed five protein binding regions. Deletion and mutation analysis shows that one of these five protein binding regions is essential for promoter activity. Gel shift experiments indicate that a sequence element resembling the GT-I and GT-II motifs of the SV40 enhancer is important for the Xwnt-1 promoter activity in vivo.