A BMP-4-dependent transcriptional control element in the 5′ flanking region of Xenopus SCL gene

We isolated 5.5kb genomic DNA fragment of Xenopus stem cell leukemia (SCL) that contains approximately 1.5kb of the 5^′ flanking region and 4.0kb of the first intron between a non-coding exon (exon 1) and a coding exon (exon 2). Sequencing result of the 5^′ flanking region has shown that there is a portion that shares 85% and 69% with the sequences of avian and mammalian genomes of SCL promoter region (-64 to +73). The 1.5kb 5^′ flanking region of SCL genome and various deletion constructs were inserted at the upstream of luciferase (luc) gene and used for the reporter assay. The reporter activity was first detected at the neurula stage in the embryos injected with -167+157/luc at the 2-cell stage and the values increased as the stages advanced. The experiments using dominant-negative constructs revealed that the activation of SCL transcription via the 5^′ flanking region requires the BMP-4 and GATA factors. Taken together with the in situ hybridization analysis indicating that expression of SCL was downregulated in the central nervous system in BMP-depleted embryos, the proximal sequence of SCL consists of a stage-dependent and BMP signaling-dependent control element.