| Cell-cell signaling through the Notch receptor mediates a wide variety of cell fate decisions during development. This signaling follows a highly conserved core pathway: activation of Notch by its ligand Delta causes the cleavage and nuclear translocation of the intracellular domain of Notch (Nintra), which then acts as a co-activator for the sequence-specific transcription factor Suppressor of Hairless [Su(H)]. Part of the specificity of the pathway, despite its broad deployment, comes from the particular subset of target genes activated by Nintra and Su(H) at any particular site. Knowledge of the identity and role of these downstream targets is crucial to understanding how Notch signaling actually mediates cell fate decisions in different settings.; We have discovered eight new targets of the Notch pathway in Drosophila; all are members of a novel gene family, the Bearded (Brd) family. We show that the Brd family genes are clustered in two genomic complexes: the Bearded complex [Brd-C] and the Enhancer of split complex [E(spl)-C]. In the E(spl)-C, they are interspersed with seven other Notch targets, the E(spl) basic-helix-loop-helix (bHLH) repressors. For each of these Brd family members, we present its sequence, expression pattern, and misexpression phenotype; we also present some data on the transcriptional regulation of these genes.; Finally, we focus on E(spl) m6, which is expressed in a subset of adult muscle precursor cells, an expression pattern unique among known Notch target genes. We examine the transcriptional regulation of E(spl) m6, which appears to respond both to N signaling and to the mesoderm-specific bHLH activator Twist. We also demonstrate that deletion of the E( spl)m6 gene results in defects in muscle development. |
