Cell-type specificity of short-range transcriptional repressors.

Transcriptional repressors can be classified as short- or long-range, according to their range of activity. Functional analysis of identified short-range repressors has been carried out largely in transgenic Drosophila, but it is not known whether general properties of short-range repressors are evident in other types of assays. To study short-range transcriptional repressors 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 repressors in Drosophila and mammalian cells, whereas Knirps is active only in insect cells. The restricted activity of Knirps, in contrast to that of Giant, suggests that not all short-range repressors possess identical activities, consistent with recent findings showing that short-range repressors act through multiple pathways. The mammalian repressor Kid is more effective than either Giant or dCtBP in mammalian cells but is inactive in Drosophila 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 introduced by transient transfection, carried on episomal elements, or stably integrated. This broad activity indicates that the context of the target gene is not critical for the ability of short-range repressors to block transcription, in contrast to other repressors that act only on stably integrated genes.