BACKGROUND: Protein interactions control the regulatory networks underlying 
developmental processes. The understanding of developmental complexity will, 
therefore, require the characterization of protein interactions within their 
proper environment. The bimolecular fluorescence complementation (BiFC) 
technology offers this possibility as it enables the direct visualization of 
protein interactions in living cells. However, its potential has rarely been 
applied in embryos of animal model organisms and was only performed under 
transient protein expression levels.
RESULTS: Using a Hox protein partnership as a test case, we investigated the 
suitability of BiFC for the study of protein interactions in the living 
Drosophila embryo. Importantly, all BiFC parameters were established with 
constructs that were stably expressed under the control of endogenous promoters. 
Under these physiological conditions, we showed that BiFC is specific and 
sensitive enough to analyse dynamic protein interactions. We next used BiFC in a 
candidate interaction screen, which led to the identification of several Hox 
protein partners.
CONCLUSION: Our results establish the general suitability of BiFC for revealing 
and studying protein interactions in their physiological context during the 
rapid course of Drosophila embryonic development.