Cell-type specificity of short-range transcriptional repressors

Transcriptional repressors can be classified as short- or long-range, accor ding to their range of activity. Functional analysis of identified short-ra nge repressors has been carried out largely in transgenic Drosophila, but i t is not known whether general properties of short-range repressors are evi dent in other types of assays. To study short-range transcriptional repress ors in cultured cells, we created chimeric tetracycline repressors based on Drosophila transcriptional repressors Giant, Drosophila C-terminal-binding protein (dCtBP), and Knirps. We find that Giant and dCtBP are efficient re pressors in Drosophila and mammalian cells, whereas Knirps is active only i n insect cells. The restricted activity of Knirps, in contrast to that of G iant, suggests that not all short-range repressors possess identical activi ties, consistent with recent findings showing that short-range repressors a ct through multiple pathways. The mammalian repressor Kid is more effective than either Giant or dCtBP in mammalian cells but is inactive in Drosophil a cells. These results indicate that species-specific factors are important for the function of the Knirps and Kid repressors. Giant and dCtBP repress reporter genes in a variety of contexts, including genes that were introdu ced by transient transfection, carried on episomal elements, or stably inte grated. This broad activity indicates that the context of the target gene i s not critical for the ability of short-range repressors to block transcrip tion, in contrast to other repressors that act only on stably integrated ge nes.