Groucho proteins are abundant and broadly expressed nuclear factors that lack 
intrinsic DNA-binding activity but can interact with a variety of DNA-binding 
proteins. The recruitment of Groucho to specific gene regulatory sequences 
results in transcriptional repression. In both invertebrates and vertebrates, 
Groucho family members act as important regulators of several signaling 
mechanisms, including the Notch, Wingless/Wnt and Dpp/BMP/TGF-beta signaling 
pathways. Recent studies of embryonic development in several species point to an 
important role for Groucho in the regulation of multiple patterning and 
differentiation events. Moreover, a deregulated expression of human Groucho 
family members is correlated with several neoplastic conditions. Here we focus 
on the functions of Groucho proteins during body patterning and their 
implication in tumorigenesis.