EVOLUTIONARILY CONSERVED POSITIVE AND NEGATIVE CIS-ACTING ELEMENTS CONTROL THE BLASTODERM-SPECIFIC EXPRESSION OF THE DROSOPHILA-SERENDIPITYALPHA-CELLULARISATION GENE

The serendipity alpha (sry alpha) cellularisation gene is only transcr ibed at the blastoderm stage, when this morphogenetic event takes plac e. We show that a 95 bp sry alpha upstream region is sufficient for bl astoderm-specific expression of a lacZ reporter gene. This region enco mpasses four nucleotide motifs (I-IV, 5' to 3') conserved at similar r elative positions in several Drosophila species. Removal of motif I le ads to ectopic expression of lacZ in precursor cells of the PNS. Delet ion of motif IV decreases the level of lacZ transcripts and modifies t heir banded pattern of accumulation late in cycle 14, whereas deletion of motifs II and III abolishes the sry alpha promoter activity. Motif III includes a consensus recognition site for b-HLH proteins. A point mutation in this E-box both severely reduces lacZ expression at blast oderm and prevents its ectopic expression in the PNS upon deleting mot if I. These two effects depend upon da+ activity, suggesting that daug hterless may positively control sry alpha transcription.