BEADEX ENCODES AN LMO PROTEIN THAT REGULATES APTEROUS LIM-HOMEODOMAINACTIVITY IN DROSOPHILA WING DEVELOPMENT - A MODEL FOR LMO ONCOGENE FUNCTION

Formation of the dorsal-ventral axis of the Drosophila wing depends on activity of the LIM-homeodomain protein Apterous (Ap). Here we report that Ap activity levels are modulated by dLMO, the protein encoded by the Beadex (Bx) gene. Overexpression of dLMO in Bx- mutants interfere s with Apterous function. Conversely, Bx loss-of-function mutants fail to down-regulate Apterous activity at late stages of wing development , Biochemical analysis shows that dLMO protein competes for binding of Apterous to its cofactor Chip. These data suggest that Apterous activ ity depends on formation of a functional complex with Chip and that th e relative levels of dLMO, Apterous, and Chip determine the level of A pterous activity. The dominant interference mechanism of dLMO action m ay serve as a model for the mechanism by which LMO oncogenes cause can cer when misexpressed in T cells.