INDEPENDENT REGULATORY ELEMENTS IN THE UPSTREAM REGION OF THE DROSOPHILA BETA-3 TUBULIN GENE (BETA-TUB60D) GUIDE EXPRESSION IN THE DORSAL VESSEL AND THE SOMATIC MUSCLES

The beta 3 tubulin gene (beta Tub60D) is a structural gene expressed d uring mesoderm development from the extended germ band stage onward. E xpression within the individual mesodermal derivatives is guided by di fferent control elements. The upstream regions allow expression in the dorsal vessel and the somatic mesoderm while enhancers localized in t he first intron guide expression in the visceral mesoderm. Deletion an alysis carried out in transgenic flies revealed independent regulatory elements for the dorsal vessel and the somatic mesoderm. For expressi on in the somatic mesoderm, a 279-bp region is absolutely essential. T his region contains a binding site for the Drosophila myocyte-specific enhancer binding factor 2 (D-MEF2), a MADS-box transcription factor k nown to be essential for mesoderm development. Deletion or mutation of this D-MEF2 binding site strongly reduces transcription. This pattern is consistent with the strongly reduced expression of beta 3 tubulin in D-mef2 mutant embryos. This analysis furthermore reveals that the D -MEP2 binding site acts in concert with nearby cis regulatory elements . These data show that the upstream control region of the beta 3 tubul in gene is an early target of the D-MEF2 transcriptional activator. (C ) 1998 Academic Press.