Abstract
Neurogenesis in all animals is triggered by the activity of a group of basic helix-loop-helix transcription factors, the proneural proteins, whose expression endows ectodermal regions with neural potential. The eventual commitment to a neural precursor fate involves the interplay of these proneural transcriptional activators with a number of other transcription factors that fine tune transcriptional responses at target genes. Most prominent among the factors antagonizing proneural protein activity are the HES basic helix-loop-helix proteins. We have previously shown that two HES proteins of Drosophila, E(spl)mgamma and E(spl)m7, interact with the proneural protein Sc and thereby get recruited onto Sc target genes to repress transcription. Using in vivo and in vitro assays we have now discovered an important dual role for the Sc C-terminal domain. On one hand it acts as a transcription activation domain, and on the other it is used to recruit E(spl) proteins. In vivo, the Sc C-terminal domain is required for E(spl) recruitment in an enhancer context-dependent fashion, suggesting that in some enhancers alternative interaction surfaces can be used to recruit E(spl) proteins.
Highlights
Sc (Scute) and E(spl)m7 (Enhancer of split m7) are two Drosophila bHLH1 transcription factors, characterized by the basic-helix-loop-helix structural motif, which is responsible for dimerization and DNA binding (2)
We have recently described a second mechanism through which target genes of proneural proteins can be repressed by HES proteins
It is worth noting that the E(spl)m7 Orange domain, a domain found in all HES family bHLH proteins (16), is dispensable for its interaction with Sc
Summary
Sc (Scute) and E(spl)m7 (Enhancer of split m7) are two Drosophila bHLH1 transcription factors, characterized by the basic-helix-loop-helix structural motif, which is responsible for dimerization and DNA binding (2). We have previously shown (1) that two HES proteins of Drosophila, E(spl)m␥ and E(spl)m7, interact with the proneural protein Sc and thereby get recruited onto Sc target genes to repress transcription.
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