dCtBP mediates transcriptional repression by Knirps, Kruppel and Snail in the Drosophila embryo

The pre-cellular Drosophila embryo contains 10 well characterized sequence- specific transcriptional repressors, which represent a broad spectrum of DN A-binding proteins. Previous studies have shown that two of the repressors, Hairy and Dorsal, recruit a common co-repressor protein, Groucho, Here we present evidence that three different repressors, Knirps, Kruppel and Snail , recruit a different co-repressor, dCtBP Mutant embryos containing diminis hed levels of maternal dCtBP products exhibit both segmentation and dorsove ntral patterning defects, which can be attributed to loss of Kruppel, Knirp s and Snail activity. Tn contrast, the Dorsal and Hairy repressors retain a t least some activity in dCtBP mutant embryos. dCtBP interacts with Kruppel , Knirps and Snail through a related sequence moth, PXDLSXK/H, This moth is essential for the repression activity of these proteins in transgenic embr yos. We propose that dCtBP represents a major form of transcriptional repre ssion in development, and that the Groucho and dCtBP co-repressors mediate separate pathways of repression.