Drosophila single-minded represses gene transcription by activating the expression of repressive factors

The Drosophila single-minded gene controls CNS midline cell development by both activating midline gene expression and repressing lateral CNS gene exp ression in the midline cells. The mechanism by which Single-minded represse s transcription was examined using the ventral nervous system defective gen e as a target gene. Transgenic-lacZ analysis of constructs containing fragm ents of the ventral nervous system defective regulatory region identified s equences required for lateral CNS transcription and midline repression. Eli mination of Single-minded:Tango binding sites within the ventral nervous sy stem defective gene did not affect midline repression. Mutants of Single-mi nded that removed the DNA binding and transcriptional activation regions ab olished ventral nervous system defective repression, as well as transcripti onal activation of other genes. The replacement of the Single-minded transc riptional activation region with a heterologous VP16 transcriptional activa tion region restored the ability of Single-minded to both activate and repr ess transcription. These results indicate that Single-minded indirectly rep resses transcription by activating the expression of repressive factors. Si ngle-minded provides a model system for how regulatory proteins that act on ly as transcriptional activators can control lineage-specific transcription in both positive and negative modes. (C) 2001 Academic Press.