Characterization of cis-regulatory elements controlling repo transcription in Drosophila melanogaster.

The glial cells missing (gcm) gene has been identified as a "master regulator" of glial cell fate in the fruit fly Drosophila. However, gcm is also expressed in and required for the development of larval macrophages and tendon cells. Thus, the Gcm protein activates the transcription of different sets of genes in different developmental contexts. How the Gcm protein regulates these different outcomes is not known. Our goal is to identify proteins that collaborate with Gcm to promote the transcriptional activation of Gcm target genes specifically in glial cells, or prevent their activation in the other tissues in which Gcm is expressed. To address this, we have focused on the transcriptional regulation of a well-characterized glial-specific Gcm target gene, the transcription factor reversed polarity (repo). We aim to understand how the transcription of the glial-specific Gcm target gene repo is regulated by Gcm and other factors. Previously we defined a 4.3 kb cis-regulatory DNA region that recapitulates the endogenous Repo expression pattern dependent on multiple Gcm binding sites. We proposed that there may be multiple cis-regulatory sub-regions that drive cell-specific expression independent of Gcm binding sites. Here, using lacZ reporter activity in transgenic lines, we have characterized three cis-regulatory elements: 1) a distal element that promotes expression in dorsolateral epidermis; 2) a repressor element that suppresses expression in the epidermis; and, 3) a proximal element that promotes expression in a subset of cell body glia. Most significantly, we have defined a minimal cis-regulatory element that recapitulates the endogenous repo expression pattern dependent on a single Gcm binding site.