A screen for co-factors of Six3

The vertebrate Six3 gene a homeobox gene of the Six-family, plays a crucial role in early eye and forebrain development. Here we report the isolation of candidate factors that interact with Six3 in a yeast two-hybrid screen. Among these are two basic helix loop helix (bHLH) domain containing proteins. Biochemical analysis reveals that the bHLH proteins ATH5, ATH3, NEUROD as well as ASH1 interact specifically with XSix3. By defining the interacting domains we show that the bHLH domain of NEUROD interacts with the SIX domain of XSix3. The co-expression of the interacting molecules during late retina determination/differentiation suggests a new role for Six3 and the respective interaction partner also in these late steps of eye development.